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All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on November 11, 2015, 08:23:06 PM

Title: .257 cal Monocoque PCP
Post by: rsterne on November 11, 2015, 08:23:06 PM
For some time now I have been contemplating what my winter project should be, now that the Motel is slowing down, and the snow is fast approaching.... This is the time of year when I get to play in the shop, and bring to life things I have been thinking about all summer.... This year's project is very ambitious, a scratch built rifle using only a few purchased parts.... the barrel, trigger group, scope, the fasteners, and a few small items like the gauge, picatinny rail and mounts, etc.... Here is a sketch of the general arrangement.... 

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/257_Benchrest_Rifle_GA_zpsvxr1xh1z.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/257_Benchrest_Rifle_GA_zpsvxr1xh1z.jpg.html)

This gun is a monster.... It's 48" long, with a 33" barrel, and will weigh an estimiated 12 lbs. plus scope.... It's heart will be a 7" twist, .257 cal TJ's barrel from a new mandrel I am having made.... The fast twist is necessary to tame the new 113 gr. Bob's Boattail bullet I designed, which is basically a scaled down version of the 200 gr., .308 cal "Whiteout" BBT that won the 200 yd. EBR in October.... This is its intended fodder.... Molds will hopefully soon be available from NOE....

(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/257-113-FN_BT_113_gr_Sketch_zpso7ulddpq.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/257-113-FN_BT_113_gr_Sketch_zpso7ulddpq.jpg.html)

In order to push that bullet into the mid 900s, I will be using 3800 psi, normally supplied by tethering to a regulator on a 4500 psi Great White tank.... However, the reservoir, which is made from 1.25" OD x 0.095" wall CrMoly, will be 400 cc, so I should be able to get a few shots off tether within a 1-2% ES.... The main tube runs the full length of the rifle, and houses the valve, hammer, hammer spring and preload adjustment.... and provides a mount for the PRod trigger group and a home-made adjustable stock, to be machined mostly from aluminum, and a short Picatinny rail up front to mount a BiPod.... The hammer has it's own cocking knob, and it's free-floating, ie when the gun is uncocked it rattles around in the ~0.1" space between the valve stem and the captive spring guide.... The 1/4" diameter steel spring guide slides through an adjusting screw mounted in a block bolted into the tube.... It carries the long hammer spring, preloaded to between 5-10 lbs. of force when uncocked, which maximizes the hammer velocity without requiring more than 20 lbs. of force when cocked.... I have used this arrangement before, and I really like it.... It makes for a lighter and more constant cocking effort, and not having the hammer spring in constant contact with the hammer, and yet lots of preload, reduces or eliminates hammer bounce.... The preload adjustment is made through the end of the main tube with a long socket wrench....

The exciting part of this design, to me, is what has been deemed the "Monotube" upper structure.... This is a 1.25" OD x 0.065" CrMoly tube that runs nearly full length.... The breech block, which will be machined from 2024-T3 round bar for a sliding fit inside the tube, extends from about 4" ahead of the loading port to the back of the tube.... In that one piece, it mounts the barrel, serves as the chamber, transfer and loading port, and bolt carrier.... It will be solidly bolted inside the tube, and the barrel threaded into it securely.... On top of the tube will be a Picatinny rail for the scope, bolted to the tube and breech block, ahead of the loading port.... At the front of the tube is a short aluminum plug, which is a close fit on the barrel, also bolted into the tube, 1" from the front.... The muzzle of the barrel (recessed just inside the tube) will be threaded 1/2"-20 NF, and a stack of Belleville disc springs will slide over it, and be tensioned by a simple 1/2" nut, tightened by a socket wrench.... By using a stack of five, 0.073" thick Bellevilles in a series arrangement, I can achieve an adjustable tension of up to 1300 lbs. on the barrel in two turns of the nut, with a corresponding amount of compression in the outer tube.... Once the tension is applied, the barrel, tube, breech block and scope mount will work as one solid piece.... The object is the maximum possible rigidity, approaching that of a solid 1.25" diameter barrel with the breech machined into it, but at a fraction of the weight.... Not a lightweight, for sure, but light for how solid it is.... There is a simple, double-concave aluminum spacer at the back, between the two tubes, holding them 1/4" apart (so the barrel tube is free floating), with through bolts securing the breech block in the upper tube to the valve and hammer spring carrier in the lower tube.... holding the two tubes parallel....

The most expensive part of the whole thing is the Millet 6-25 x 56 SF Scope (obtained from Eric at http://www.scopesandammo.com (http://www.scopesandammo.com)) which my wife will be giving me for Christmas.... It is massive, 22" long with sunshade, and weighs 2.2 lbs., built around a 35mm tube.... The MilDot-with-bar Reticle is calibrated for the maximum magnification (25X) which means the dots are far enough apart to allow sighting at 100 yards and have the top of the lower post be the point of aim at 200 yards.... The distance from the dot-to-bar becomes 1 Mil at 12.5X, and that point is marked on the zoom ring, so at that setting you have a MilDot reticle, but with 10 dots available in every direction.... The Elevation turret has 140 MOA of travel because of the huge 35mm tube, which should allow enough to reach out about 1/4 mile.... I will be machining a 20 MOA slope in the Picatinny rail so that the trajectory intersects the line of sight at 100 yards with the scope centered.... Hold under, using the MilDots, will be used at ranges under 100 yards.... Funny thing is that the scope doesn't look at all out of place on such a long rifle....

I've ordered the barrel mandrel, and the CrMOly tubing and 2024-T3 bar stock.... and Mrs. Claus ordered the scope.... so this project is off and running.... and I can't wait to start making chips....

Bob
Title: Re: .257 cal Monotube PCP
Post by: Motorhead on November 11, 2015, 08:38:05 PM
woof  .... or, is that WooF or perhaps WOOF !

Bench gun to be sure or at least in some serious buffalo sticks.
Looks like a cool project Bob , will be watching this one  ;)
Title: Re: .257 cal Monotube PCP
Post by: Monkeydad1969 on November 11, 2015, 08:59:01 PM
Man, Bob...You're definitely in BEAST MODE now!
Title: Re: .257 cal Monotube PCP
Post by: dcorvino on November 11, 2015, 09:25:12 PM
Very nice project Bob.
Look forward to reading about your progress.

Dave
Title: Re: .257 cal Monotube PCP
Post by: Matt15 on November 11, 2015, 10:38:36 PM
Looks very cool Bob!!!  8) 8)
Title: Re: .257 cal Monotube PCP
Post by: Monkeydad1969 on November 11, 2015, 10:56:15 PM
Can you go into detail about the valve setup?
Title: Re: .257 cal Monotube PCP
Post by: rsterne on November 11, 2015, 11:12:30 PM
I have a feeling you're asking about the hammer, not the valve, but here are preliminary drawings for both.... These are subject to change....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/257_Benchrest_Valve_zpstjzgpl70.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/257_Benchrest_Valve_zpstjzgpl70.jpg.html)

The valve is pretty conventional.... It will be made from 2024-T3 aluminum, sized to fit the tube, which is the same ID as an MRod.... It is quite a bit longer, and incorporates the gauge port in the front portion.... The mid-body is 11/16" ID (the tap drill size for 3/4"-16 threads which fasten the two halves together), and the front passage is 13/32" (a tapered valve spring is used), so that there is no restriction on air getting into the valve and around the 3/8" OD PEEK poppet which has a 1/8" stem made from O1 drill rod.... The exhaust port is on a 30* angle and will be made by plunging with a 7/32" end mill, and then walking the mill around slightly to round out the hole at the mating face with the transfer port.... The transfer port will be made from 1/2" OD Teflon rod, long enough to get a slight crush fit against the breech block, so that it will seal.... The transfer port will be about 0.26" ID, and the barrel port, which is actually machined into the breech block (at a 30* angle to the boreline), will be oblong to maintain bore-size area, without making the port wider than 80% of the bore.... This will mean it will be about 5/16" long at the chamber.... So, the port at the chamber will be slightly over 0.20 x 0.30".... The goal is to have bore-area porting throughout the system.... The valve throat will be either 19/64" or 5/16", so that the throat area (once you subtract the stem area) will be about 10% larger than the bore.... The valve will be secured in the tube by three 1/4"-28 SHCSs 1/4" long, with the heads set into the valve for extra strength.... plus two 10-32 screws which secure the upper tube to the lower tube, by bolting the breech to the valve....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/257_Benchrest_Hammer_zpsf56mdcz5.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/257_Benchrest_Hammer_zpsf56mdcz5.jpg.html)

The hammer (green in the drawing) is pretty conventional, it will be made from 1144, easy to work, but can be hardened easily after machining.... It will have its own cocking handle, protruding through the side of the tube, below and in front of the bolt handle.... It will be about 1.75" long, and will have a stroke of 1.5", plus the valve lift, which I estimate at about 0.1" maximum.... I just have to make sure that the sear on the PRod hammer can't flip up behind it, so may use a resilent spacer / impact donut to prevent overtravel.... The difference is in the way the hammer spring (yellow) is contained and adjusted.... It rides on a long, 1/4" diameter steel spring guide (red), with a spring seat on the front that fits the drilled hole in the hammer.... The guide passes through the preload/position adjusting bolt (purple) and on the back is threaded and has a locknut installed which prevents the end of the spring guide from contacting the hammer when the hammer is sitting against the valve stem.... About 0.1" of clearance is "normal", but that amount can be adjusted by the (purple) bolt, which can be turned from the back of the tube with a deep socket (like a spark-plug socket).... As you move the guide forward, towards the hammer, you increase the distance the spring is compressed when you cock the gun, and vice versa.... The nut (red) on the back of the spring guide adjusts the preload on the spring when the gun is uncocked.... Normally, if the spring doesn't touch the back of the hammer, there is no preload.... By using this arrangement, you can have the preload as much as half the total spring force when cocked, and yet have the hammer floating around loose when uncocked.... When you fire the gun, the nut on the end of the spring guide hits the adjusting bolt and stops the spring, allowing the hammer to carry on from it's own momentum and open the valve.... I will be adding an O-ring on the stem of the guide to cushion that impact, you can see that in the drawing....

This allows you to do several things.... First, with significant preload on the end of the spring guide, if the hammer is thrown back against it by the valve closing, it can't compress the spring unless it is thrown back with greater force than the preload.... If it can't compress the spring, there is nothing to fling the hammer back against the valve stem and knock the valve open a second time (hammer bounce), wasting air after the bullet has left the barrel.... So that gap, combined with the preload on the spring, acts as a Hammer Debounce Device (HDD).... Using a very loose, but very stiff hammer spring often saves air for that very reason.... The hammer can't hit it hard enough to open the valve a second time on rebound.... but this arrangement is even more effective because a simply loose spring has no load when the hammer first hits it on rebound, so will still compress and send the hammer forward again.... In this arrangement, the hammer has to strike the end of the guide with a force greater than the preload to even move it....

Secondly, if you have ever used a short, stiff spring to try and avoid hammer bounce, you will have quickly found out that the gun is hard to cock.... and sometimes you will fail to cock it by accident because you have to pull so hard right at the very end of the cocking stroke.... By comparison, a longer, lighter spring is much nicer to cock because for the same total hammer energy the initial force is higher, and the final force is lower (keeping the average cocking force about the same).... Seldom will you fail to cock the gun, because your muscles are already pulling with some force at the beginning, and the force doesn't increase suddenly right at the end of the stroke.... The problem is, that arrangement is much more prone to air-wasting hammer bounce, and the worst situation is when you only have zero to a small amount of preload.... the hammer can go crazy, like a machine-gun, and empty the reservoir.... With this captive spring guide arrangement, you can set the preload to 1/3, or even 1/2 of the maximum force when cocked.... You have to pull harder right at the beginning of the cocking stroke, but the force doesn't go from zero to ridiculous.... it goes from medium to heavier.... Since the hammer energy is determined by the AVERAGE force accelerating it, and the distance that force acts through (ft.lbs.), you get the same result with less acceleration to start with but more towards the end.... but the gun is much more pleasant (and reliable) to cock, and the peak force is less.... Plus, when the valve throws the hammer back when it closes, it meets with the spring guide with a bunch of preload on it, and so the spring is very unlikely to store any energy to fling the hammer back, open the valve again, and waste air.... I already proved this concept in my "Grizzly", here is a photo of that arrangement....

(http://i378.photobucket.com/albums/oo221/rsterne/Flying%20Dragon%20PCP/Limited%20Stroke_zpskvdgiaqn.jpg) (http://s378.photobucket.com/user/rsterne/media/Flying%20Dragon%20PCP/Limited%20Stroke_zpskvdgiaqn.jpg.html)

The large hollow screw with the square end is the preload/position adjuster.... The two nuts to the right of it are threaded onto the end of the spring guide and locked against each other.... Instead of having no preload on a heavy spring, that took over 20 lbs. to cock.... this arrangement has 7 lbs. of preload, and cocks at about 18 lbs.... and I can no longer hear the B-R-A-A-A-P of hammer bounce wasting air....

Bob
Title: Re: .257 cal Monotube PCP
Post by: YEMX on November 11, 2015, 11:25:35 PM
I can't wait to see the progress!!!! 
Title: Re: .257 cal Monotube PCP
Post by: Prouzy on November 11, 2015, 11:33:43 PM
Very nice design and

"Once the tension is applied, the barrel, tube, breech block and scope mount will work as one solid piece.... "

is super cool! Very well thought out. Looking forward to it coming to fruition.
Title: Re: .257 cal Monotube PCP
Post by: Gippeto on November 12, 2015, 12:13:26 AM
I will be using 3800 psi... the reservoir, which is made from 1.25" OD x 0.095" wall CrMoly,

Bob

 ???

What CrMoly Bob?
Title: Re: .257 cal Monotube PCP
Post by: rsterne on November 12, 2015, 12:19:17 AM
Sorry guys, I posted the drawings before I wrote the text above to go with them....  :-[

Al, I'm using Normalized 4130, Tensile 97K and Yield 63K.... 3:1 safety margin to yield at 3764 psi.... 11,292 psi at yield, and 17,387 psi at burst.... Over 4.5:1 to burst at 3800 psi....

Bob
Title: Re: .257 cal Monotube PCP
Post by: Tofazfou on November 12, 2015, 12:22:44 AM
I will be using 3800 psi... the reservoir, which is made from 1.25" OD x 0.095" wall CrMoly,

Bob

 ???

What CrMoly Bob?
4130 Chromoly
Title: Re: .257 cal Monotube PCP
Post by: Tofazfou on November 12, 2015, 12:24:22 AM
For some time now I have been contemplating what my winter project should be, now that the Motel is slowing down, and the snow is fast approaching.... This is the time of year when I get to play in the shop, and bring to life things I have been thinking about all summer.... This year's project is very ambitious, a scratch built rifle using only a few purchased parts.... the barrel, trigger group, scope, the fasteners, and a few small items like the gauge, picatinny rail and mounts, etc.... Here is a sketch of the general arrangement.... 

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/257_Benchrest_Rifle_GA_zpsvxr1xh1z.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/257_Benchrest_Rifle_GA_zpsvxr1xh1z.jpg.html)

This gun is a monster.... It's 48" long, with a 33" barrel, and will weigh an estimiated 12 lbs. plus scope.... It's heart will be a 7" twist, .257 cal TJ's barrel from a new mandrel I am having made.... The fast twist is necessary to tame the new 113 gr. Bob's Boattail bullet I designed, which is basically a scaled down version of the 200 gr., .308 cal "Whiteout" BBT that won the 200 yd. EBR in October.... This is its intended fodder.... Molds will hopefully soon be available from NOE....

(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/257-113-FN_BT_113_gr_Sketch_zpso7ulddpq.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/257-113-FN_BT_113_gr_Sketch_zpso7ulddpq.jpg.html)

In order to push that bullet into the mid 900s, I will be using 3800 psi, normally supplied by tethering to a regulator on a 4500 psi Great White tank.... However, the reservoir, which is made from 1.25" OD x 0.095" wall CrMoly, will be 400 cc, so I should be able to get a few shots off tether within a 1-2% ES.... The main tube runs the full length of the rifle, and houses the valve, hammer, hammer spring and preload adjustment.... and provides a mount for the PRod trigger group and a home-made adjustable stock, to be machined mostly from aluminum, and a short Picatinny rail up front to mount a BiPod.... The hammer has it's own cocking knob, and it's free-floating, ie when the gun is uncocked it rattles around in the ~0.1" space between the valve stem and the captive spring guide.... The 1/4" diameter steel spring guide slides through an adjusting screw mounted in a block bolted into the tube.... It carries the long hammer spring, preloaded to between 5-10 lbs. of force when uncocked, which maximizes the hammer velocity without requiring more than 20 lbs. of force when cocked.... I have used this arrangement before, and I really like it.... It makes for a lighter and more constant cocking effort, and not having the hammer spring in constant contact with the hammer, and yet lots of preload, reduces or eliminates hammer bounce.... The preload adjustment is made through the end of the main tube with a long socket wrench....

The exciting part of this design, to me, is what has been deemed the "Monotube" upper structure.... This is a 1.25" OD x 0.065" CrMoly tube that runs nearly full length.... The breech block, which will be machined from 2024-T3 round bar for a sliding fit inside the tube, extends from about 4" ahead of the loading port to the back of the tube.... In that one piece, it mounts the barrel, serves as the chamber, transfer and loading port, and bolt carrier.... It will be solidly bolted inside the tube, and the barrel threaded into it securely.... On top of the tube will be a Picatinny rail for the scope, bolted to the tube and breech block, ahead of the loading port.... At the front of the tube is a short aluminum plug, which is a close fit on the barrel, also bolted into the tube, 1" from the front.... The muzzle of the barrel (recessed just inside the tube) will be threaded 1/2"-20 NF, and a stack of Belleville disc springs will slide over it, and be tensioned by a simple 1/2" nut, tightened by a socket wrench.... By using a stack of five, 0.073" thick Bellevilles in a series arrangement, I can achieve an adjustable tension of up to 1300 lbs. on the barrel in two turns of the nut, with a corresponding amount of compression in the outer tube.... Once the tension is applied, the barrel, tube, breech block and scope mount will work as one solid piece.... The object is the maximum possible rigidity, approaching that of a solid 1.25" diameter barrel with the breech machined into it, but at a fraction of the weight.... Not a lightweight, for sure, but light for how solid it is.... There is a simple, double-concave aluminum spacer at the back, between the two tubes, holding them 1/4" apart (so the barrel tube is free floating), with through bolts securing the breech block in the upper tube to the valve and hammer spring carrier in the lower tube.... holding the two tubes parallel....

The most expensive part of the whole thing is the Millet 6-25 x 56 SF Scope (obtained from Eric at http://www.scopesandammo.com (http://www.scopesandammo.com)) which my wife will be giving me for Christmas.... It is massive, 22" long with sunshade, and weighs 2.2 lbs., built around a 35mm tube.... The MilDot-with-bar Reticle is calibrated for the maximum magnification (25X) which means the dots are far enough apart to allow sighting at 100 yards and have the top of the lower post be the point of aim at 200 yards.... The distance from the dot-to-bar becomes 1 Mil at 12.5X, and that point is marked on the zoom ring, so at that setting you have a MilDot reticle, but with 10 dots available in every direction.... The Elevation turret has 140 MOA of travel because of the huge 35mm tube, which should allow enough to reach out about 1/4 mile.... I will be machining a 20 MOA slope in the Picatinny rail so that the trajectory intersects the line of sight at 100 yards with the scope centered.... Hold under, using the MilDots, will be used at ranges under 100 yards.... Funny thing is that the scope doesn't look at all out of place on such a long rifle....

I've ordered the barrel mandrel, and the CrMOly tubing and 2024-T3 bar stock.... and Mrs. Claus ordered the scope.... so this project is off and running.... and I can't wait to start making chips....

Bob

I for 1 am very excited to hear and see all the details on this baby.

WOW!
Title: Re: .257 cal Monotube PCP
Post by: Gippeto on November 12, 2015, 01:22:57 AM
Sorry guys, I posted the drawings before I wrote the text above to go with them....  :-[

Al, I'm using Normalized 4130, Tensile 97K and Yield 63K.... 3:1 safety margin to yield at 3764 psi.... 11,292 psi at yield, and 17,387 psi at burst....

Bob

That's odd Bob...when I run it through the calculator using 1.25" od x .095" wall, 63100psi and 3:1 it comes out to 3197psi.

http://www.engineersedge.com/calculators/pipe_bust_calc.htm (http://www.engineersedge.com/calculators/pipe_bust_calc.htm)


You using something different to calc it?

Al
Title: Re: .257 cal Monotube PCP
Post by: rsterne on November 12, 2015, 02:24:33 AM
I'm using the spreadsheet you and I built at the CAF a few years ago.... Burst pressure = 2* Tensile * Tube Wall / Tube ID.... Yield  pressure = 2* Yield * Tube Wall / Tube ID.... Nothing is changed.... That calculator must be using tube OD instead of ID as we discussed.... Perhaps to add an additional safety factor?....

Here is the document you referenced on the CAF which we used when I made that spreadsheet.... http://www.energypipe.com/barlowsformula.htm (http://www.energypipe.com/barlowsformula.htm)

It gives Barlow's formula for thin wall tubes ((Wall / ID) <0.1) as:

P = (2*S*T) / (OD-2T) * SF

Since ID = (OD - 2T) .... we get P = (2*S*T) / (ID * SF) .... This uses the ID rather than the OD....

Bob....
Title: Re: .257 cal Monotube PCP
Post by: Gippeto on November 12, 2015, 05:18:45 AM
Don't think it was me helping with the spread sheet...Excel and I are not well acquainted . Fired up the calculator and arrived at the same point as you did.

Have been using that calculator for years and never noticed...good catch...again. ;)

Al





Title: Re: .257 cal Monotube PCP
Post by: dyotat100 on November 12, 2015, 08:54:01 AM
That is what I came up with last night. Was talking to Tom last night to verify the numbers for chromoly. When I saw the material I questioned it because I had a Haley and it was 1.125".095. That's just over 3500 psi with that tubing.

http://www.engineersedge.com/calculators/pipe_bust_calc.htm (http://www.engineersedge.com/calculators/pipe_bust_calc.htm)

Title: Re: .257 cal Monotube PCP
Post by: rsterne on November 12, 2015, 11:51:34 AM
Al, it was me who wrote the spreadsheet in Excel, while you and I were working on all the math.... I just kept adding all the formulas for hoop strength, bolt shear, bearing load, and tearout, and also for thread shear, and the tensile load on the remaining tube wall until it was all in one spreadsheet.... I kept checking the numbers as we progressed, and right at the end double checked everything to make sure my spreadsheet agreed with the math you came up with.... I've been using it every since.... although I have been questioned on it a couple of times when guys used some of the calculators on the internet.... I'm pretty sure that the one on Engineer's Edge, and some others, use the OD just to add some additional safety margin.... Better too strong than not strong enough, right?....

I learned the other day that....

Quote
Compressed gas cylinders that are subject to DOT regulations have a
design safety factor of 3.4 based on the ultimate material tensile strength.
In other words, the stress at the maximum working pressure is ~29%
of the stress at failure.

Using that as an additional calculation to the 3:1 to yield might be a good idea, no?.... Using the conservative calculator on Engineer's edge (which uses OD), and using the 97K tensile for normalized 4130, my 1.25" OD x 0.095" wall tubing has a MSWP of 4336 psi.... I'm NOT going to lose any sleep over it at 3800 (3.9:1 to burst)....

Bob
Title: Re: .257 cal Monotube PCP
Post by: Gippeto on November 12, 2015, 01:42:57 PM
Sleep is too important to be loosing any...a point that really hits home when you're not getting enough. ;)








Title: Re: .257 cal Monotube PCP
Post by: Bill G on November 12, 2015, 05:07:53 PM
This will be very interesting with 1:7 twist.  My eye is on this one.
Title: Re: .257 cal Monotube PCP
Post by: Gertrude on November 13, 2015, 01:20:13 AM
As usual, Very Impressive Bob !

so is it safe to say, this is not going to be your new "Grouse gun" ? ? ? LOL!
Title: Re: .257 cal Monotube PCP
Post by: rsterne on November 13, 2015, 01:32:03 AM
Maybe for taking their head off at 200 yards?.... It they'll keep it still instead of bobbing all over, that is.... *LOL*....

I hope I haven't bitten off more than I can chew, with this one....  ::)

Bob
Title: Re: .257 cal Monotube PCP
Post by: sixshootertexan on November 13, 2015, 08:55:04 AM
I think you can handle it Bob. Interesting design on the breech. How far do you plan on stretching it out?
Title: Re: .257 cal Monotube PCP
Post by: rsterne on November 13, 2015, 02:03:35 PM
Realistically, I will find trouble getting a bench setup at even 200 yards where I usually shoot, let alone further out.... I may end up making a portable bench and target stand that I can take apart and put in the back of my Rhino SXS to take into the mountains to setup.... The plan is to sight in the gun at 100 yards, which by machining a 20 MOA downslope into the bottom of the Picatinny rail I plan to accomplish with the scope near optical center.... In the 6" long rail, that is about 0.035" slope on the bottom, which I will remove at the same time I machine it to fit the outside of the 1.25" Monotube.... If I can get the bullet into the upper 900s, with the BC that I hope to achieve, that should put me on target at the top of the bottom post in the reticle at 25 X at 200 yards.... If not, I can simply zoom out a bit, at 20X I will gain what amounts to one MilDot (ie 4 dots up at  20X the equivalent of dots up at 25X).... Resighting the gun for 200 yards will need about 18 MOA of "up" dialed into the turret, which is less than built into the rail, so no different than sighting in at 100 yards without the ramp.... To go further out, if the gun is shooting well enough, and I have the opportunity, I would use first the MilDots to get on paper, and then crank the turret up more.... When sighted at 200 yards, at 20X the top of the bottom post should be just over 300 yards.... Crank in another 20 MOA to recenter there (a total of ~ 38 MOA), and the post will put me at about 400 yards.... add another 22 MOA (a total of 60 MOA, now getting close to the end of the 70 MOA Elevation adjustment available in the scope), and by using the top of the post that would put me at about 500 yards.... Basically, the plan is to leapfrog one distance from the last, alternating using the MilDot to get on paper with adjusting the turrets.... Anything beyond that would require changing the slope of the Picatinny rail.... but let's face it, if I ever hit ANYTHING at 500 yards I'd be bouncing off the walls....   :o

So that's how I expect the sighting system to work out, and it's limitations.... Can I, or the rifle, ever do it?.... We can all dream, can't we?.... First let me get the gun built (a big challenge right there) and see how it shoots at 100 yards.... IMO, if you can't achieve 2 MOA at a given distance, there is no point in trying to get out further.... You're just fooling yourself....  ::) ... or maybe you're just having fun?....  8)

Bob
Title: Re: .257 cal Monotube PCP
Post by: Rizen 1 on November 13, 2015, 05:49:01 PM
Very nice Bob!  I can't wait to see this one!!!
Title: Re: .257 cal Monotube PCP
Post by: Bill G on November 15, 2015, 11:30:38 AM
Maybe for taking their head off at 200 yards?.... It they'll keep it still instead of bobbing all over, that is.... *LOL*....

I hope I haven't bitten off more than I can chew, with this one....  ::)

Bob

No way.
Title: Re: .257 cal Monotube PCP
Post by: rsterne on November 15, 2015, 01:22:51 PM
I liked the term Monotube, but since there is an air tube under it (making two tubes), it doesn't quite fit.... The upper tube takes all the loads keeping the critical parts (barrel, breech, and scope) aligned, like an Exoskeleton, so that makes it a Monocoque design.... From now on, I will be referring to it as my "Monocoque Design PCP"....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rjorge on November 15, 2015, 03:22:18 PM
Great work so far! I am sure this will be another build where the experience shared and lessons learned will be very meaningful to those working with the .257 cal and FPE levels. I hope you exceed your goals! ;)
Title: Re: .257 cal Monocoque PCP
Post by: Tomg on November 16, 2015, 11:19:03 AM
Peaked my interest, dialed in:-)

Title: Re: .257 cal Monocoque PCP
Post by: LeadBreakfast on November 16, 2015, 07:56:53 PM
Very cool! Love that you designed it to work with your own bullets as well. I'll come along for this ride!
Title: Re: .257 cal Monocoque PCP
Post by: UCChris on November 17, 2015, 02:35:52 AM
This one is going to be epic. Subscribed.
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on November 18, 2015, 01:48:43 PM
I have most of the materials coming to start work on this project.... I do need, however, a small block of aluminum for the front bipod mount.... I need a piece 1.5" x 2" x 2".... and 6061-T6 would be suitable, no need for anything fancier.... Anybody have a piece kicking around their shop you can spare?....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on November 18, 2015, 06:10:12 PM
I have been looking at my supply of hammer springs for this project.... I needed a long, rather weak spring for the captive spring guide concept, and it turns out that using two QB (like) hammer springs riding on one guide should work perfectly.... The ones I have are actually 0.36" OD x 0.051" wire x 2.4" long, but they have the same spring rate and length as a QB spring.... Stacking two of them end to end gives a spring of the following specs....

LOA 4.80"
Rate 9 lb/in.
Max. travel 2.70"
Max. force 24 lbs.

There are two adjustments, the preload on the spring (set by the length of the spring guide, which is adjustable).... and the distance the end of the guide is clear of the inside of the hammer when uncocked (which sets the distance that the spring is compressed when the gun is cocked), also adjustable.... The hammer pulls back 1.50" from touching the valve stem to being cocked.... Here is a table of the various combinations....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Hammer%20Spring%20Adjustments_zps0vmcdrmh.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Hammer%20Spring%20Adjustments_zps0vmcdrmh.jpg.html)

The columns, left to right, are (distances in inches, forces in lbs.):
The distance the spring is compressed by the guide (preload);
The force required to do that (also the force at the beginning of the cocking stroke);
The distance the spring is compressed during cocking (the guide is clear of the inside of the hammer by 1.50" minus that distance) ("D") ;
The total distance the spring is compressed when cocked;
The force required to do that (force when cocked);
The average force over the travel of the hammer ("F") ;
The energy given to the hammer during the firing stroke (F x D / 12) ....

As you can see, I can vary the hammer energy from 1.0 - 2.0 FPE, and I am expecting to need about 1.4-1.5 FPE, so I should have no problem finding a setting that will work.... When I actually make the spring guide and adjuster I will post a photo of it....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on November 18, 2015, 10:07:55 PM
Well, I made the first part today.... Amazing how something as simple as a spring guide and adjuster takes so long to make.... Here it is....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Spring%20Guide%20and%20Adjuster_zps2ikqssks.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Spring%20Guide%20and%20Adjuster_zps2ikqssks.jpg.html)

The spring guide is made from a piece of 1/4" drill rod 6.5" long.... It is threaded 1/4"-NF for 1.25" at the back, and carries two nuts, locked against each other, and a bumper made of a 90D # 108 O-ring.... The guide is also threaded at the front for another nut, which is held with Loctite bearing mount and then turned to provide a spring seat and fit loosely inside the hammer.... The adjuster is a 9/16"-NF bolt 2" long (which I had to anneal before machining) drilled through 1/4" and then counterbored to 3/8" for a depth of 1/2" to accommodate the length of the two springs, which total 4.8" long.... They are 0.36" OD x 0.051" wire.... As pictured, the spring is under 0.8" of preload (4" fitted length) and it takes about 7.25 lbs. to move it.... That is how hard the hammer would have to hit it on rebound to store any energy in the spring, so I think the chances of hammer bounce are very small.... It will take about 20 lbs. of force to cock the gun, which is high but certainly manageable.... The chart in the previous post shows the large range of adjustability....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: MJP on November 18, 2015, 11:38:59 PM
Nice design Bob, have been thinking something similar to avoid threads between frame and airtube.
One thing less to machine and when using stainless it's not so much fun cutting threads all the time.
Really looking forward seeing the finished gun.

Marko
Title: Re: .257 cal Monocoque PCP
Post by: dyotat100 on November 19, 2015, 01:19:30 PM
I'm sure I have something close to what you need Bob. Have to check tonight or tomorrow though
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on November 19, 2015, 01:57:06 PM
Hey, Doug.... I have a piece on the way, thanks!....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Bill G on November 19, 2015, 05:41:45 PM
LOL I should have scrolled down a hair more and would have seen your post. disregard the PM.

Bill
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on November 21, 2015, 07:17:25 PM
My Christmas present from my dear wife came in today....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Millet%20Scope_zpsdry93ruw.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Millet%20Scope_zpsdry93ruw.jpg.html)

Millet 6-25 x 56mm SF.... Just another scope you say?.... well, yes, but this may give you a hint about what is different about it.... those are 1" rings for comparison....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Millet%20Rings_zps2jsxv228.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Millet%20Rings_zps2jsxv228.jpg.html)

Yes, the tube is 35mm, and the scope is 22" long with sunshade and weighs 2 lb. 13 oz. with the rings.... Here is it sitting beside a Leapers 3-9 x 32mm AO with sunshade....   :o

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Millet%20vs%20Leapers_zpscghk0ql3.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Millet%20vs%20Leapers_zpscghk0ql3.jpg.html)

The scope is very bright and clear.... It focuses down to 15 yards, and has 140 MOA of Elevation adjustment.... I will be machining the Picatinny rail it mounts on to a 20 MOA angle on the bottom, which should put me on target at 100 yards with the scope still on optical center.... The 1/2 MilDot Reticle is calibrated at 25 X, and there is a mark at 12.5 X, which makes each 1/2 MilDot work out to a full MilDot, so that works out to a lot of holdover just using the dots....

Bad part is, I have to put it away until Christmas....   ::)

Bob
Title: Re: .257 cal Monocoque PCP
Post by: n4spd on November 21, 2015, 08:50:17 PM
wow. anyone allowed to be in your work around are really lucky.  good luck and thanks for sharing.  subscribed as well...
Title: Re: .257 cal Monocoque PCP
Post by: Rizen 1 on November 21, 2015, 09:36:43 PM
I love "EARLY" Christmas presents!  Looking good Bob!
Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on November 21, 2015, 10:39:58 PM
Wow Bob!! That is a big scope!!
Title: Re: .257 cal Monocoque PCP
Post by: Erockrocket on November 23, 2015, 04:57:37 PM
 That is a fat tubed scope!  Very nice Christmas gift.
I am anxious to see what kind of beast you build. I am planning a caliber change this winter, gonna go with .257. I have a place I can stretch out to 500+yds. I have a few questions about barrel length and power needed, I will start a new thread soon.
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on November 26, 2015, 01:25:23 PM
The bulk of the materials arrived yesterday, and I spent the day finalizing most of the design.... It doesn't look much like an airgun at the moment....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Monocoque%20PCP%20Materials_zpsxtgeb1yc.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Monocoque%20PCP%20Materials_zpsxtgeb1yc.jpg.html)

Plastic pipe is for the forestock and cheek piece.... 1 1/4" OD CrMoly tubing for the monocoque upper tube (0.065" wall) and air reservoir (0.095" wall).... The 1 1/8" 2024-T3 Aluminum round bar is for the breech block, valve, front plug, and all other internal mounts.... The rectangular aluminum barstock is for the external parts; the spacer between the tubes, the adjustable stock mounts, and the front bipod/stock mount....

Soon to be converted into a pile of chips, and usable parts, I hope....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Job on November 26, 2015, 05:32:31 PM
No more it cannot wait
(http://cdn3.teen.com/wp-content/uploads/2013/10/world-without-books-gifs-tv.gif)
Title: Re: .257 cal Monocoque PCP
Post by: Bruce on November 26, 2015, 07:20:50 PM
Bob!!!!! You sly dog!

Now I want to do another build lol

Going to be fun to follow this one!

Bruce

Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on November 26, 2015, 08:19:14 PM
Good luck!!
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on November 29, 2015, 08:59:49 PM
The block of aluminum from Watertown arrived and I wanted to see how my new 1-1/4" drill bit worked so the first thing I did was square it off to size and drill it to fit on the Reservoir.... That went perfectly, although there is a lot more to do, machine the Forestock Mount into it and a Picatiinny Rail in the bottom.... The Forestock is a piece of 1-1/4" (ID) black plastic pipe 12" long that slides over the reservoir.... and a piece of it 6-1/2" long, split down the middle, will be used for the Cheekpiece.... Here are those parts....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Cheekpiece%20and%20Bipod%20Mount_zpsqcu2v2y1.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Cheekpiece%20and%20Bipod%20Mount_zpsqcu2v2y1.jpg.html)

Inside the Cheekpiece are two "washers" made from 3/8" aluminum, which will form the mounts.... One will be attached to the back of the Breech, and the other to the bracket that mounts the Buttplate to the Reservoir Tube.... arranged like this....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Cheekpiece%20Assembly_zpsemxdj0u7.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Cheekpiece%20Assembly_zpsemxdj0u7.jpg.html)

Most of today's work went into making the Stock Bracket, which is shown in the photo below....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Stock%20Mount%20Bracket_zpscppjzsic.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Stock%20Mount%20Bracket_zpscppjzsic.jpg.html)

It is machined from a piece of 3/4" x 1-1/2" 6061-T6 aluminum about 5" long.... The large hole fits over the back of the Reservoir Tube and will clamp in place with set-screws.... The screws at the top will mount the rear washer that holds the Cheekpiece.... The three threaded holes at the bottom are for mounting the Buttplate, and an optional 4" wide Baseplate that can sit flat on a bench.... Here is what it looks like in side view....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Stock%20Mount_zpszpw3cc5l.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Stock%20Mount_zpszpw3cc5l.jpg.html)

The height of the Buttplate will be adjustable in height, tilt, and length of pull, using a threaded rod, locked by a wing nut as shown.... The center position for the front of the Buttplate is 1" behind the bracket, so it should be good and rigid.... By offsetting the threaded rod by 1/8" in the Buttplate, and with the 1/2" spacing on the holes, I will be able to alter the height below the line of sight over a 1-1/4" range in 1/4" increments (3 holes x 2 positions per hole)....

It is great to finally start making chips.... Next up will be finishing the Cheekpiece mounting washers, and completeing the BiPod / Forestock mount....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on November 29, 2015, 09:37:23 PM
Looking good Bob!!
Title: Re: .257 cal Monocoque PCP
Post by: MJP on November 30, 2015, 05:47:44 AM
Nice looking work Bob, what kind of machine you got? First rough cutting with a mill and looks like belt sander finish? Waiting to see the finished gun, most interesting.

Marko
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on November 30, 2015, 12:51:10 PM
My "mill" is a milling attachment for my 40yo Atlas 12x36 lathe.... It lacks the rigidity for precision work, so tends to leave tool marks.... I use a sanding block and sand by hand to get the finish you see.... I kind of like it, and leave my aluminum parts natural.... The biggest limitation is that it only has 6" of horizontal travel, and 3" of vertical, and the vice measures 1" x 2.5".... It's a real challenge to figure out how to hold parts sometimes....

(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/WebToolPostDrill.jpg) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/WebToolPostDrill.jpg.html)

Above photo shows using it as a tool-post grinder.... *LOL*....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: MJP on November 30, 2015, 01:33:22 PM
Nice, good old fashion creativity I really do respect that. That's one thing I like about this forum, like minded mad scientists around.  ;D
The sanded finish looks good, sometimes it's hard to decide to paint or not to paint or blue parts.
I use an old Victoria U2 milling machine at home with rotary table and milling head tilts 360deg in Y and X axis. And have a full machineshop at work, but that just makes me lazy.

Marko
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on November 30, 2015, 02:19:01 PM
Nice.... Sometimes I feel like I'm machining with one hand tied behind my back.... *LOL*.... No wonder everything takes me so long....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on November 30, 2015, 11:49:21 PM
Spent most of the day putting up Christmas decorations for the Motel today.... but did manage to get a couple more things done in the shop.... I drilled the two donuts that hold the Cheekpiece in place, drilled the mounting holes in the Cheekpiece, tapped the holes in the rear donut and mounted the back of the Cheekpiece.... I also made a stand that attaches to the bottom of the Stock Bracket instead of a conventional Buttstock to use when shooting from a bench.... It will help hold the rifle level, and act as a compliment for the front BiPod....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Stock%20Bracket%20with%20Cheekpiece%20and%20Stand_zps2b66y02i.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Stock%20Bracket%20with%20Cheekpiece%20and%20Stand_zps2b66y02i.jpg.html)

It is 4" wide at the base, so will have lots of stability.... You simply remove the Buttstock and bolt this on instead.... Not a lot of progress, but at least some today....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 02, 2015, 12:34:11 AM
I got most of the BiPod made today, and did some more work on the Block that will mount it to the gun.... Here is the adjustable BiPod....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/BiPod_zpsg2lukq9l.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/BiPod_zpsg2lukq9l.jpg.html)

It doesn't look like much, but I think it should function well.... The crossbar, which will bolt to the mount on the gun, is made from a piece of 3/4" x 1" wide 6061-T6 barstock.... It is drilled and tapped for two pieces of 1/2" threaded rod.... The pieces shown are 8" long and 12" apart, and should allow for an elevation relative to the bench of about 6 degrees (360 MOA).... I can make longer rods, or they can just sit on a block of wood to raise the muzzle further relative to the bench if necessary.... The wheels are 2-1/2" OD pulleys with a 1/2" bore, setscrewed to the shaft, with a nut tightened up against them and secured with green Loctite.... The ends of the nuts are radiused so that when you rotate the rods, using the pulleys as handwheels, they won't hang up on the bench, allowing easy height adjustment in very small increments.... There are wingnuts to lock the height, which increases the rigidity of the assembly as well....It is remarkably stable, and I think with the easy adjustment should prove an asset to shooting from the bench.... It will bolt to the mount below....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/BiPod%20and%20Stock%20Mount_zpsrrwyyylu.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/BiPod%20and%20Stock%20Mount_zpsrrwyyylu.jpg.html)

There is still more work to do to this (you are looking at the bottom of it).... I still have to cut the slots in the Picatinny rail, and drill and tap either side of that for the screws that will bolt the BiPod above to it when shooting from the bench.... The boss on the side facing you fits inside the plastic pipe I'm using for the Forestock, and keeps it positioned so that the top of the pipe is touching the top of the reservoir, offset downwards.... As you can see, the boss is not concentric with the hole for the tube.... This will be attached to the reservoir with setscrews.... I hope to complete these parts tomorrow, and then it will be time to start on the internal parts....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 02, 2015, 08:47:25 PM
I finished off the Mount for the Forestock and BiPod today.... Here it is with the Forestock in place.... The Picatinny Rail is done now....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Forestock%20and%20Mount_zps2mayt6n7.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Forestock%20and%20Mount_zps2mayt6n7.jpg.html)

I also completed the BiPod.... It now bolts to the mount with two #10 SHCSs and has a built in level to check the cant.... which is easily adjustable with the handwheels on the threaded rods.... which are just above the bench....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/BiPod%20and%20Mount_zpsme3ij8kk.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/BiPod%20and%20Mount_zpsme3ij8kk.jpg.html)

Used in combination with the plate on the bottom of the rear Stock Mount, which completes the TriPod, the rifle will be easy to adjust to any required elevation by using the handwheels, and then a final set of the cant using the bubble....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 03, 2015, 01:53:19 AM
Made up a mount for the Scope Rail to hold it for machining to cut the radius on the bottom and put in 40 MOA of angle.... This was a time consuming and nerve-wracking job.... Here is the results....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Scope%20Rail%20Top_zpsztiqxne5.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Scope%20Rail%20Top_zpsztiqxne5.jpg.html)

You will notice that the height of the lower portion of the rail is less at the front (left) than at the back.... The difference in the 6" long rail is just under 0.070" which works out to 40 MOA and should put me pretty close to the optical center of the scope at 200 yards.... I had to add one more mounting screw at the back....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Scope%20Rail%20Bottom_zpsqageqhqs.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Scope%20Rail%20Bottom_zpsqageqhqs.jpg.html)

I machined the taper into the bottom using a 1-1/4" diameter carbide router bit I got from China for less than $15 including postage.... It cuts very smoothly, and the radius fits the tube perfectly.... Setting the scope rail up so that I could machine it was tricky, though.... I had to bolt it to a backing strip of aluminum (1 x 1.5") with screws in 2 of the 3 holes and move the screws along so that I could machine the entire length.... I was JUST able to manage it without having to move the jig in the milling attachment....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 03, 2015, 08:00:22 PM
This is one of those days you almost dread, and then feel great when it's over..... provided everything works the way it should.... The spacer between the two tubes is 10" long and concave on top and bottom to fit the 1-1/4" diameter tubes, and keep them parallel and 1/4" apart.... It could have been made from a piece of 3/4" x 1" aluminum bar stock, but the only piece I had long enough was 1-1/2" wide.... so the first thing I had to do was saw it lengthwise and then mill it to 1" wide.... Since it was 10" long and I can only machine a bit over 6" of length, that required two setups, and they were critical to match up parallel and exactly 1" wide.... Fortunately, that setup of the vice on the milling attachment on my lathe was also necessary for milling both sides to a radius using the 1-1/4" diameter router bit I just bought.... but again it meant two setups per side, critical that the part be square to the machine in both axis to end up with the same thickness at the center of the web from end to end, to end up with the tubes parallel in height.... and also with the grooves centered in the width of the part, to make sure the tubes end up parallel side to side.... I'm pleased to say that it went very well.... Here is the finished blank....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Tube%20Spacer_zpsculrnkl8.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Tube%20Spacer_zpsculrnkl8.jpg.html)

It fits the tubes perfectly, in fact better than previous breeches where I have machined the bottom with a ball-end mill.... I would definitely use a carbide router bit for this job again, especially with them being a fraction of the cost of a high-speed steel ball-end mill.... It needs to be run fairly fast, with not too deep a cut.... I was running 1270 RPM and removing 0.020" per pass once the full width of the router was engaged.... and using the power cross-feed, that was smoother than going by hand.... Including shallower finishing passes, that meant for about 15-17 passes per setup, times 6 (including milling the width to 1"), so about 100 passes.... It took me 5 hours to produce the piece you see above.... There is a bit more machining to do to this part, it has to be drilled for the transfer port and the three bolts that fasten the upper and lower tubes together.... plus a recess in one end to hold the back of the Forestock in place.... However, that won't happen until the tubes are finished and this will be machined to match.... Besides, I've had enough for one day.... It's time to have a drink and relax.... It's been a very productive few days, and it's time for a break....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: MJP on December 04, 2015, 12:50:59 AM
That is nice, this is just the kind of work where the skill and experience comes to play, knowing the limitations of your machines and working around to do what's needed regardless of the limitations.
Good work there Bob. Those are the kind of parts where I'm happy that I spend all that money on an old good mill. To know that I can take 900mm long pass.  ;)
But still I don't have a lathe, I can turn short pieces on the mill chuck but longer ones are must be done at work.
Keep up the good work, enjoying to see it coming together.

Marko
Title: Re: .257 cal Monocoque PCP
Post by: YEMX on December 04, 2015, 09:23:06 AM
Looking good Bob!!!  This rifle is going to be awesome!!
Title: Re: .257 cal Monocoque PCP
Post by: Bill G on December 04, 2015, 07:38:18 PM
This is one of those days you almost dread, and then feel great when it's over..... provided everything works the way it should.... The spacer between the two tubes is 10" long and concave on top and bottom to fit the 1-1/4" diameter tubes, and keep them parallel and 1/4" apart.... It could have been made from a piece of 3/4" x 1" aluminum bar stock, but the only piece I had long enough was 1-1/2" wide.... so the first thing I had to do was saw it lengthwise and then mill it to 1" wide.... Since it was 10" long and I can only machine a bit over 6" of length, that required two setups, and they were critical to match up parallel and exactly 1" wide.... Fortunately, that setup of the vice on the milling attachment on my lathe was also necessary for milling both sides to a radius using the 1-1/4" diameter router bit I just bought.... but again it meant two setups per side, critical that the part be square to the machine in both axis to end up with the same thickness at the center of the web from end to end, to end up with the tubes parallel in height.... and also with the grooves centered in the width of the part, to make sure the tubes end up parallel side to side.... I'm pleased to say that it went very well.... Here is the finished blank....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Tube%20Spacer_zpsculrnkl8.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Tube%20Spacer_zpsculrnkl8.jpg.html)

It fits the tubes perfectly, in fact better than previous breeches where I have machined the bottom with a ball-end mill.... I would definitely use a carbide router bit for this job again, especially with them being a fraction of the cost of a high-speed steel ball-end mill.... It needs to be run fairly fast, with not too deep a cut.... I was running 1270 RPM and removing 0.020" per pass once the full width of the router was engaged.... and using the power cross-feed, that was smoother than going by hand.... Including shallower finishing passes, that meant for about 15-17 passes per setup, times 6 (including milling the width to 1"), so about 100 passes.... It took me 5 hours to produce the piece you see above.... There is a bit more machining to do to this part, it has to be drilled for the transfer port and the three bolts that fasten the upper and lower tubes together.... plus a recess in one end to hold the back of the Forestock in place.... However, that won't happen until the tubes are finished and this will be machined to match.... Besides, I've had enough for one day.... It's time to have a drink and relax.... It's been a very productive few days, and it's time for a break....

Bob

nice job Bob.  When working with soft materials like aluminum  and even free machining steel, router bits are the best bang for the buck.  Light cuts high rpm and fair feed rates make for no more time than with a traditioal form cutting end mill. And as you said, pennies in comparison.
Title: Re: .257 cal Monocoque PCP
Post by: Motorhead on December 04, 2015, 07:45:19 PM
Now punch mill some 5/8 to 3/4 holes down its length to take away some weight ... or not ?

* being holes would be against tubes you would never see it  ;)
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 05, 2015, 01:29:55 AM
On a 12+ lb. gun, with a 2.8 lb. scope, I would never notice the difference.... *LOL*.... Sliced my hand up today in the shop, so progess will be delayed a bit....  :-[

Bob
Title: Re: .257 cal Monocoque PCP
Post by: William on December 05, 2015, 01:38:33 AM
On a 12+ lb. gun, with a 2.8 lb. scope, I would never notice the difference.... *LOL*.... Sliced my hand up today in the shop, so progess will be delayed a bit....  :-[

Bob
Sorry to hear that Bob, I hope it wasn't too bad. I wish you a speedy recovery and please be careful.

You project is looking really good, cant wait to see it finished.

William
Title: Re: .257 cal Monocoque PCP
Post by: scottyhazzard on December 05, 2015, 05:28:48 AM
Careful, I truly enjoy the thread but not at the cost of your hand or digits. I hope you heal quickly and painlessly. It's going to be along winter, so pace yourself and take care of you.
Title: Re: .257 cal Monocoque PCP
Post by: Bruce on December 05, 2015, 09:23:45 AM
Bob,

I hope you heal fast! So unfortunate that you got hurt.

Bruce
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 07, 2015, 11:13:38 PM
I received my new 33" Barrel today.... it slugged out right at 0.257" groove as requested, with a 7" twist.... I set to work fitting it to the Breechblock which I had previously drilled 1/2" all the way through.... I drilled the front to 33/64" and tapped it to a depth of 2" with 9/16"-18 NF threads, and then counterbored it 3/4" deep to 9/16" to fit the OD of the barrel.... The Barrel was turned down on the end to 3/8" to fit inside a steel Thimble which will carry the barrel port, next there is a 1/2" diameter portion to fit the bore of the Breechblock, and then the threads.... This was all done in a 4-jaw chuck so that it was concentric to the bore.... There is an O-ring which is compressed to seal the Barrel to the Thimble, and simultaneously seal the Barrel into the ID of the Breechblock when it is tightened against the Thimble.... Here is a photo of the Barrel machining, the roughed out Breechblock (made from 1-1/8" OD 2024-T3 round bar), and the two screwed together....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Barrel%20Machining_zpsmorrkgnz.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Barrel%20Machining_zpsmorrkgnz.jpg.html)

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Barrel%20and%20Breechbolck_zpsqkxdsiwt.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Barrel%20and%20Breechbolck_zpsqkxdsiwt.jpg.html)

My hand is on the mend, it felt good to get back into the shop today.... Tomorrow I hope to turn the OD of the Breechblock to fit inside the upper CrMoly Monocoque tube.... Once the rough fitting is done, there will be a lot of work required to finish and mount the Breechblock in the Monocoque tube....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on December 08, 2015, 08:36:41 AM
Glad you are back to building! Nice work!!






Boy I wish I could afford a lathe and milling machine.
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 08, 2015, 12:28:56 PM
I wish I could afford a BIGGER one!!!

Bob
Title: Re: .257 cal Monocoque PCP
Post by: MJP on December 08, 2015, 12:53:19 PM
Cost is not the issue in bigger machines, the big ones cost next to nothing in here, but wher the hec do you put a machine that is 3 meters tall 4m long and over 2 wide and weighs over 4.5 metric tons?
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 08, 2015, 01:00:19 PM
I agree, space is a problem at least as severe as funds.... My Atlas 12x36 lathe was passed down from my Dad, who bought it in the late 1960's.... The tooling, on the other hand, keeps me pretty much broke though.... so you can imagine how much I have left over for a lathe with a headstock bore bigger than 3/4".... or a REAL milling machine.... While I wouldn't call my setup a "toy", it certainly provides me with many challenges.... 

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on December 08, 2015, 02:00:28 PM
I wish I could afford a BIGGER one!!!

Bob

LOL! You could really make bigger and better air rifles then!!

Cost is not the issue in bigger machines, the big ones cost next to nothing in here, but wher the hec do you put a machine that is 3 meters tall 4m long and over 2 wide and weighs over 4.5 metric tons?

That would be my other problem.  :(
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 10, 2015, 12:05:03 AM
Yesterday I got a piece of 1.5" black Delrin rod from Whitewolf (thanks, Kim!) and started turning it into a Buttstock today.... After a few attempts at trying to hold it, I managed to mill off both sides to leave me with a piece 1" thick, which I have drilled and tapped for the 3/8" threaded rod as shown.... It will soon look much prettier....  :) .... The other part in the photo is the partially finished fill fitting for the front of the Air Reservoir.... It is tapped 1/8" NPT on the front for a male Foster, and the holes for the four 1/4"-28 x 1/4" SHCS retaining bolts are drilled and tapped at 90*.... It needs shortening and the O-ring groove machined yet....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Fill%20Fitting%20and%20Buttstock_zps3y8qcr0c.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Fill%20Fitting%20and%20Buttstock_zps3y8qcr0c.jpg.html)

I usually use a 5C Collet in a square holder to drill holes at 90*, but the parts for this project are over 1" diameter, so they wouldn't fit.... The solution was to turn a 1" long x 1" diam. stub on the end of each part so that I could hold it in the collet as shown below.... The other parts below are the "Barrel Stretcher" which fits inside the front of the Monocoque tube, anchored by three 10-32 x 1/4" low profile SHCSs to stand the load of the Belleville washers that will put the barrel in tension.... and the mount for the Hammer Spring Adjuster which I made previously....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Internal%20Fittings_zps8floitrn.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Internal%20Fittings_zps8floitrn.jpg.html)

The upper (long) screw in the holder for the adjuster goes through the Breechblock (below the bolt) and the spacer, securing the rear of the two tubes together.... The shorter (lower) screw just mounts it into the lower tube, and will have a short piece of Delrin rod inside the hole pressing against the side of the 9/16" bolt that carries the spring guide, to lock the adjustment in place....

I also got the 10" long Breechblock turned to fit inside the Monocoque tube today, which prepares it for some of the machining to come.... I still have to make the Valve and Hammer.... Then comes the difficult job of machining the 4 foot long CrMoly tubes to hold everything....   ::)

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on December 10, 2015, 08:28:54 AM
Looking Good!!  8)
Title: Re: .257 cal Monocoque PCP
Post by: LeadBreakfast on December 10, 2015, 05:08:58 PM
making great progress, this is going to be quite the setup when complete
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 10, 2015, 10:56:58 PM
This morning I finished up the Buttstock.... It turned out quite well, with lots of adjustment.... The LOP can be varied from 13-15", and the drop is adjustable over a range of 1-1/4" in 1/4" increments.... The shaft in the butt pad is 1/8" off center, so 1/2 turn changes the height of the butt by 1/4" and then there are three holes on 1/2" centers.... The threaded rod is glued and pinned into the butt pad, as well as threaded, and the wingnut locks the rotation....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Stock_zpsp7bkmt8l.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Stock_zpsp7bkmt8l.jpg.html)

This afternoon I did most of the machining on the Breechblock insert.... pretty much everything except the slot for the bolt handle.... I will have to duplicate everything you see here in the Monocoque tube, so accuracy and layout is the key here.... I'm quite pleased with the way it turned out....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Breechblock%20Top_zpsltwptp71.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Breechblock%20Top_zpsltwptp71.jpg.html)


(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Breechblock%20Bottom_zps02nefdji.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Breechblock%20Bottom_zps02nefdji.jpg.html)

The two holes with low profile 10-32 screws in them are to take the tension load of the barrel when the Belleville washer stack at the muzzle is compressed.... There are three screws that bolt the upper and lower tubes together, a 10-32 at the back and two 8-32s forward,  either side of the transfer port.... The transfer port is milled at a 30* angle towards the muzzle to ease the flow transition into the barrel.... The Picatinny scope rail bolts to the Breechblock though holes in the Monocoque tube, with the forward screw tapped into the tube itself.... The opening for loading is milled flush with the centerline of the bore on the right side, and just past the vertical centerline, so just over 1/4 of the material has been removed.... This should make the assembly much more rigid vertically than milling out the entire top half of it.... There will be a steel thimble (actually in 2 pieces) that will have the barrel port, chamber, and loading tray machined into it.... The 8-32 screw under it will take the end force trying to push it back on firing.... It is set deeply so that the head is in shear for extra strength.... I will likely mill the slot for the bolt handle into both the Monocoque tube and the Breechblock in one operation after they have been assembled.... or possibly machine the tube first, then install the Breechblock into it and mill the slot through the slot in the tube.... I'm sure it will be the most difficult part of the whole procedure....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: LeadBreakfast on December 11, 2015, 07:54:49 PM
Looking great Bob!
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 11, 2015, 08:26:48 PM
Today I machined the double convex Tube Spacer to match the Breechblock, as the mounting screws and transfer port penetrate it to connect the two tubes.... The recess in the middle is a pocket to clear the barrel tensioning retainer screw....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Spacer%20Machining_zpsz0ohvowo.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Spacer%20Machining_zpsz0ohvowo.jpg.html)

On the bottom at the front I had to machine a recess that will hold the Forestock tube in place tight against the top of the Reservoir.... you can see it in the photo below.... I also got the Hammer made today, including the cocking handle, as shown....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Hammer%20and%20Spacer_zps8y8efoth.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Hammer%20and%20Spacer_zps8y8efoth.jpg.html)

The total weight of the Hammer and handle is 182 grams, and it will have a total travel of 1.5".... The captive spring arrangement and adjuster was shown previously, and the moving part weighs 53 g. for a total of 235 g.... That means that only 77% of the total energy ends up in the Hammer, the rest is absorbed by the O-ring on the guide when it comes to a halt before the hammer coasts the last bit to open the valve.... That is the price you pay for easier cocking and less Hammer bounce....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: PakProtector on December 11, 2015, 08:27:49 PM
Cost is not the issue in bigger machines, the big ones cost next to nothing in here, but wher the hec do you put a machine that is 3 meters tall 4m long and over 2 wide and weighs over 4.5 metric tons?

LOL...I almost got my hands on a K&T No.3 vertical mill. 15 hp. Nearly new, hours-wise. Comically the first thing that slowed me down was it had only a feed option for the Z...then the 6800 lbs left wondering if I'd tilt my garage floor. The next pole barn is going to get a 10" thick floor wid plenty ov re-bar in it...:)
cheers,
Douglas
Title: Re: .257 cal Monocoque PCP
Post by: TPL on December 12, 2015, 06:52:38 AM
Recently I could of bought an old CNC-lathe in excellent condition very cheap but as I have a flat on third floor no place here either. Doesn't fit into my balcony nor I have electrical supply big enough.

Frustrating.
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 12, 2015, 06:30:01 PM
Today I attached the Front Cheekpiece Mount to the back of the Breechblock....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Front%20Cheekpiece%20Mount_zps1sxxcu53.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Front%20Cheekpiece%20Mount_zps1sxxcu53.jpg.html)

It is mounted below the centerline of the tube so that the inside of the Cheekpiece tube sits against the top of the upper Monocoque tube.... I also machined the front of the barrel to fit the 1/2" ID Bellevilles and threaded it 1/2"-20 NF for the nut that will provide the barrel tension.... The aluminum sleeve that bolts into the front of the Monocoque tube is 9/16" ID to fit on the larger part of the barrel, while the Bellevilles ride on the 1/2" section....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Tensioner%20Parts_zps2xoirisu.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Tensioner%20Parts_zps2xoirisu.jpg.html)

The front of the Monocoque tube is about 1/10" ahead of the muzzle to protect the crown.... If I wish, I can use a Hatsan Air Stripper instead of the nut to tighten against the Bellevilles to provide the barrel tension and also strip the air away from the back of the bullet....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Barrel%20Tensioner_zpsetigcsea.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Barrel%20Tensioner_zpsetigcsea.jpg.html)

This completes all the parts that fit inside the Monocoque tube.... except to machine the bolt slot which I will do after machining the tube.... I am still undecided if that will be my next step, or if I will make the valve first.... and put off machining the two tubes until the end....   ::)

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 13, 2015, 08:19:45 PM
I couldn't put it off any longer, so today I did most of the machining on the Monocoque Tube.... all the holes for the various bolts, plus the loading port and transfer port are done, plus the additional 10-32 tapped hole for the front of the Picatinny scope rail.... Here is the top view....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Monocoque%20Tube%20Top_zpsf62gsgjq.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Monocoque%20Tube%20Top_zpsf62gsgjq.jpg.html)

Everything fit really well, all the bolts fit into the holes, but a couple were tight enough to require a touch with a file or Dremel bit to make them easy to assemble.... Careful deburring was the order of the day to make sure that the Breechblock didn't hang up when slid inside.... I was particularly proud of how well the loading port lined up.... Below is the bottom view, and you can see that the transfer port and mounting bolts also line up with the Spacer....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Monocoque%20Tube%20Bottom_zpsb4xhtlmh.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Monocoque%20Tube%20Bottom_zpsb4xhtlmh.jpg.html)

All in all, I am very pleased.... The key to the accurate machining was using the 5/16" hole behind the loading port where the heads of the screws are that take the tension and compression loads of the barrel and tube.... Using a 5/16" pin in the chuck of the lathe through that hole, both for setup (measuring everything from that point), and for indexing 180* for the holes on the bottom, did the trick....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on December 13, 2015, 10:34:17 PM
Wow!! It is really coming along great!!
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 14, 2015, 04:30:27 PM
Today I machined the top of the PRod trigger group to fit the 1-1/4" OD x 0.095" wall tube.... It normally fits a 7/8" OD x 0.065" wall tube, so one of the concerns is that the sear projects far enough into the thicker tube I am using to safely hold back the hammer.... I used the 1-1/4" diameter router bit I have to cut the larger radius, and at the point it barely touched the center of the recess (I removed 0.030" from the sides to get there) I stopped and checked the sear engagement.... It was about 1/32", which although I feel was perfectly safe (after all, the hammer can't raise up by more than the clearance in the tube), I decided I wanted a bit more.... I noticed that the boss in the casting that holds the sear pivot pin was about 0.010" below where the router cut, so I mounted the trigger group back in the milling attachment and milled down until I just touched the edge of that.... The arrow in the photo below points to that shiny mark, right beside the sear.....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Trigger_zpsmsfjg8tn.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Trigger_zpsmsfjg8tn.jpg.html)

With the trigger group machined to that depth, there is over 1 mm of sear engagement (I'll get an exact measurement after I cut the slot in the tube), and I'm happy with that.... One other thing that is important is that the slot in the tube to clear the sear must be slightly more than the full length of the sear.... The parts of the sear in front and behind the actual sear "bump" now project slightly above the bottom of the tube recess in the trigger group, so if the slot is too short, it would affect the engagement depth, and in fact could even prevent the sear from cocking properly.... All the other parts (the trigger and the intermediate link) are still well below the tube and do not interfere....

The PRod trigger is very strongly built, and I see no problem with it easily withstanding way more than the 20ish lb. maximum load I will be asking it to hold....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: MJP on December 15, 2015, 02:23:14 AM
That's what you get with some spare time and dedication. Good work there Bob. Waiting anxiously for the finished gun and how she will shoot.
Marko
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 16, 2015, 07:15:00 PM
Today I made the front half of the Valve, and cut the O-ring groove in the Fill Fitting while I was set up for that....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Valve%20Front%20and%20Fill%20Fitting_zpsqi0qb5ja.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Valve%20Front%20and%20Fill%20Fitting_zpsqi0qb5ja.jpg.html)

You will notice that I am using a conical valve spring to eliminate any restriction on the inlet side of the valve poppet.... I hope to work on the back half of the Valve tomorrow....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 18, 2015, 11:08:20 PM
I worked on the Valve today, and completed the machining on the body....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Valve%20Body_zpsuzqpw2vh.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Valve%20Body_zpsuzqpw2vh.jpg.html)

While the rear half was in my square Collet holder so that I could index it 90* to drill and tap the four 1/4"-28 mounting holes, I also drilled the port and the two 8-32 screw holes beside that which hold the two tubes together at the front of the Breechblock.... In addition, I screwed the valve front into place and drilled and tapped 1/8"-NPT for the gauge which mounts on the left side.... I was extremely pleased with how well everything lined up.... Here is a photo of the assembly (without the tubes)....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Valve%20Fitted%20in%20Place_zpswfbopecu.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Valve%20Fitted%20in%20Place_zpswfbopecu.jpg.html)

The two long 8-32 screws which hold everything together dropped right through the holes and screwed in with my fingers.... I still have to make the poppet, and install an O-ring seal for the stem in the back of the valve, but this is the last major internal part.... It won't be long I will be able to machine the lower tube to hold the valve, hammer, and fill fitting.... Unfortunately, I am still waiting for the 1/4" long 1/4"-28 SHCSs which hold the valve and fill fitting in place against the air pressure, so I won't be able to pressure test it until they arrive....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: William on December 18, 2015, 11:31:09 PM
Looking good Bob, it wont be long and you will be throwing lead down stream!
Everything looks clean and well fit thats for sure.

Good luck and have fun

William
Title: Re: .257 cal Monocoque PCP
Post by: oldpro on December 18, 2015, 11:54:41 PM
 This is some very fine work from a guy who claims he runs a small Inn in Canada of all places...Are we sure Bob is who he says he is?  I bet hes hiding with the witness protection system and most likely is a CIA or KGB operative and expert weapons maker. What do we really know about Bob or Mr. Bourne??? HHHmmm
Title: Re: .257 cal Monocoque PCP
Post by: Stikman on December 18, 2015, 11:57:03 PM
Travis...I think he is the armorer for Bond...James Bond....
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 18, 2015, 11:58:56 PM
*L*

Bob
Title: Re: .257 cal Monocoque PCP
Post by: oldpro on December 19, 2015, 12:26:53 AM
LOL love it,, Good work old man your skills are impressive.
Title: Re: .257 cal Monocoque PCP
Post by: Bill G on December 19, 2015, 09:35:17 AM
I'm still trying to figure out how he has the time and energy to run a lodge and be an airgun scientist and builder.  He has to have energy like my 9yr old.    ;D

Keep it up and stay young professor. 

Bill G

Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on December 19, 2015, 11:05:24 AM
Nice work!!!  How big is the valve compared to a disco?
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 19, 2015, 01:33:05 PM
The valve is the same OD as an MRod valve (and 4.25" long), but the ports are bore-size (actually, slightly over 0.257") on the outlet and huge (2.5X bore area) on the inlet side.... so the effective volume of the valve is the entire reservoir, 400cc.... In addition, there are no 90* turns in the ports, the throat of the valve is well radiused where it blends into the exhaust port, which then turns 30* into the 17/64" transfer port, and then another 30* turn into the port in the receiver, which will then blend into the barrel though an oblong port measuring 3/16" wide x 5/16" long, with NO bolt probe in the way.... The valve throat is 5/16", sealed by a 3/8" PEEK poppet on a 1/8" stem, so the throat area is 24% greater than the bore area....

You will notice that my airgun building (shop time) happens in the winter when the Motel is pretty much dead.... *LOL*.... For the rest of the year I just spend all my spare time thinking....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 19, 2015, 04:18:00 PM
I made the rest of the valve parts today.... Here is the finished poppet and stem seal....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Valve%20Internals_zpsibpl4i43.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Valve%20Internals_zpsibpl4i43.jpg.html)

The poppet is made from 3/8" diameter PEEK, and I threaded the end of the 1/8" drill rod stem to 5-40 thread, drilled the PEEK with a #38 drill (tap size for 5-40) and counterbored it 0.10" to 1/8" and then just wound the stem into the PEEK, letting it cut its own threads until it stopped.... It was so solid I couldn't back it out.... I then cut the head to length and turned it for the spring seat right on the stem.... It sealed first time.... The stem seal is a #006 70D O-ring sitting in a 1/4" diameter recess in the valve body, held in place with a short piece of 7/16" bolt faced off flat on both ends and a screwdriver slot ground in the end for installation.... It has only enough drag to barely hold the weight of the valve body, so considering the forces on this valve shouldn't even be noticed.... The inside of this valve is huge....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Valve%20Inside_zpsql2tljfr.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Valve%20Inside_zpsql2tljfr.jpg.html)

The throat  (visible in the bottom of the rear section on the left) is 5/16" ID, so the seat margin is only 0.030".... The valve is drilled 11/16" ID, leaving a 5/32" gap all the way around the poppet head (4 times the throat area).... The front of the valve is drilled 13/32", the same as the front ID of the conical valve spring, and so has twice the area of the throat, allowing the air to enter the valve from the reservoir much easier than it can get out.... I don't think there should be any problem with this valve flowing air....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on December 19, 2015, 07:04:21 PM
The valve is the same OD as an MRod valve (and 4.25" long), but the ports are bore-size (actually, slightly over 0.257") on the outlet and huge (2.5X bore area) on the inlet side.... so the effective volume of the valve is the entire reservoir, 400cc.... In addition, there are no 90* turns in the ports, the throat of the valve is well radiused where it blends into the exhaust port, which then turns 30* into the 17/64" transfer port, and then another 30* turn into the port in the receiver, which will then blend into the barrel though an oblong port measuring 3/16" wide x 5/16" long, with NO bolt probe in the way.... The valve throat is 5/16", sealed by a 3/8" PEEK poppet on a 1/8" stem, so the throat area is 24% greater than the bore area....

You will notice that my airgun building (shop time) happens in the winter when the Motel is pretty much dead.... *LOL*.... For the rest of the year I just spend all my spare time thinking....

Bob

Thanks Bob!!
Title: Re: .257 cal Monocoque PCP
Post by: Motorhead on December 19, 2015, 07:37:23 PM
Been a spell sense checking in .... Darn Mr.Bob you have been quite busy of late !
Looking more and more like something mechanical  :o tho shy of calling it an Air rifle just yet  ;D
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 19, 2015, 08:34:06 PM
Yeah, right now it is simply a growing pile of parts.... *LOL*.... About the only piece identifiable as a rifle is the rear Stock....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Lee in Texas on December 20, 2015, 12:26:48 AM
Just read the whole thread. Absolutely fascinating. Will you be making more of these to sell?
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 20, 2015, 02:00:13 AM
Nope, this is a one-of project.... I never make parts or guns to sell.... no time to get my own projects done.... *LOL*....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: oldpro on December 20, 2015, 02:04:26 AM
 Bob just for chit and giggles what would you charge to make a copy? I think people would be shocked if they knew how much something like this would cost in parts and labor for a one off.  Im guessing 3-4K if not more.
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 20, 2015, 02:08:05 AM
More.... It takes me forever with my equipment, 50% of the time or more is in setup.... and then the design time is longer than the project.... People just have no idea of the time involved....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 20, 2015, 08:15:47 PM
Today I worked on the Thimble which contains the Barrel Port and Loading Tray.... The 3/8" diameter stub on the barrel fits into the front of it to insure alignment with the bore, and the joint is sealed with an O-ring, which also seals it into the Breechblock in front of the Transfer Port.... I haven't yet machined the O-ring groove behind the transfer port in it.... The barrel port in this part was machined with a 3/16" end mill starting at 30* to match the transfer port at the back of the port, and then angled to 45* to make the front of the port longer to match the bore area.... The port ends up just over 3/16" wide x 5/16" long at the boreline, but blends into the 17/64" round transfer port.... The finishing touches were done with a Dremel....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Tray%20and%20Port%20Thimble_zpsbuu0dyii.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Tray%20and%20Port%20Thimble_zpsbuu0dyii.jpg.html)

The hole at the back fits over the head of an 8-32 screw in the bottom of the Breechblock, that takes the end load from the barrel screwing against it, and the air pressure inside it.... You can see that screw in the bottom of the loading tray in the photo below....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Loading%20Tray%20Thimble_zpsfmy5dukd.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Loading%20Tray%20Thimble_zpsfmy5dukd.jpg.html)

Once again, I am extremely pleased with the way everything fits and lines up.... This relative small part took about 6 hours to make.... Next up is the Bolt, which will carry the O-ring that seals the breech inside this Thimble.... It is the retractable style I developed a while back, with no probe to restrict the airflow.... Then comes the complicated job of machining the "J" shaped bolt slot in the Breechblock and Monocoque tube.... I'm not looking forward to that....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: YEMX on December 20, 2015, 09:49:35 PM
I should have been watching this thread more keenly- I would have sent you a hardened, taller sear for use w/a 1.25" main tube and the Prod trigger group. 

I ordered a customized Prod trigger group for use w/a Mrod tube some time ago for a build, but I personally didn't like the look or feel of it.  The sear (as you found out) has to be taller to engage the hammer, and the trigger group I ordered came with a modified sear. 

I've since swapped out the modified sear for standard one, and am using the Prod trigger group on a 13xx pumper build. 

If you'd like Bob, I would be willing to send you the sear if you need/want it.
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 20, 2015, 10:07:20 PM
Not necessary.... I machined off the top of the trigger group to fit the MRod size tube (that moves it up 0.030"), plus an extra .010".... It sticks into the tube about 0.040", I can't imagine that being an issue.... However, if you have no use for it, I would indeed like to see it, and it would cover me should the other one not work properly.... I'll PM you my address....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Bill G on December 21, 2015, 09:42:07 AM
Bob just for chit and giggles what would you charge to make a copy? I think people would be shocked if they knew how much something like this would cost in parts and labor for a one off.  Im guessing 3-4K if not more.

If we were to honestly consider the concept to design to prototype to manufacuter.  I'm gonna say $25K is a likely figure.  That being with the intent of producing for the masses.  Bob looks to have put the concept and design a LOT of consideration and it is for him not production so he effectively writes it off as entertainment.  Bob, you have a heck of an entertainment budget  :o.  lol

Bill   
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 21, 2015, 01:48:47 PM
Bill, your comments are right on.... Precisely why I never make the same gun twice.... The only time anyone gets a chance to get one of my project guns is when I tire of it and need the money for the next project.... Even that is hard to do, when you consider how little guys are willing to spend for a one-of, custom rifle.... The most I ever got was $1000 for the prototype Millenium Pumper, which barely paid for all the parts, and I have tried to sell a couple of other projects since at the same price, with no interest.... So, yes, all I can do is chalk it up to Entertainment.... I figure I have never even made $1.00 an hour, most of the time I am lucky to cover the parts....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: LeadBreakfast on December 21, 2015, 02:56:07 PM
Fantastic work! Still watching this one very closely!
Title: Re: .257 cal Monocoque PCP
Post by: scottyhazzard on December 21, 2015, 03:32:07 PM
Bob, I'm new to this so maybe I'm lacking a degree of understanding. Having said that I find it hard to believe that $1000 is the most folks would pay. Shocking really, after seeing what you do and accomplish. Especially in light of how much people pay for a production rifle! I can't fathom paying so little for so much. Still watching, this thread it's fascinating.
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 21, 2015, 05:43:59 PM
Scott, believe it.... Even though some of them follow my build threads, they have no idea of the amount of work involved, or are unwilling to pay wages that they wouldn't even get serving Fast Food.... I'm not complaining, far from it.... this situation means I can plod along at my own (retired) pace, and never have to deal with impatient customers.... I don't know how those building Custom PCPs can stand it.... I had enough of it in my 30+ years in the R/C Model Yacht business....

Today I made the Bolt, except to fit the handle, and cut the O-ring groove in the Loading Tray / Thimble behind the transfer port.... The Bolt still has to be cut off about where the line is drawn, which will be flush with the back of the Breechblock when fully open....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Bolt%20and%20Loading%20Tray_zpswnkweu1g.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Bolt%20and%20Loading%20Tray_zpswnkweu1g.jpg.html)

The Bolt has a very long travel, when it is fully forward the shoulder on the Bolt is up against the Loading Tray.... This is necessary because of the long bullet, necessitating a long loading port, plus the nose of the bolt has to go past the transfer port, which had to be far enough from the front of the loading port to allow for the O-ring to seal when retracted so that the nose of the bolt clears the back of the transfer port, without the O-ring dropping into the port when fully forward.... It will retract about 3/8" from the full forward, loading position, to the firing position....

It's time to do some more thinking to make sure I don't forget anything before I continue machining the tubes.... The Monocoque tube and Breechblock both need the slot machined for the bolt handle.... and the Reservoir tube has yet to have any machining done.... although all the internal parts are now complete....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on December 21, 2015, 08:45:07 PM
Beautiful work Bob!!
Title: Re: .257 cal Monocoque PCP
Post by: YEMX on December 22, 2015, 07:24:11 PM
The rifle is shaping up quite nicely!!  Sear is in the mail Bob!

Here's a picture of the modified sear compared to the factory sear.  Modified on top.  Sorry about the bad picture quality:

(http://i1297.photobucket.com/albums/ag38/donut_212/KIMG0012_zpsy7qgwqy3.jpg)
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 22, 2015, 07:42:32 PM
Question.... why the oval hole?....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: YEMX on December 22, 2015, 08:15:27 PM
No idea!  You'd have to talk to Mike at Citrus Airguns... He's the one who made the sear originally.
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 23, 2015, 09:49:43 PM
Only got a few hours in the shop today.... but I got the holes in the top and bottom of the lower tube machined.... That allowed me to bolt together some of the sub-assemblies for the first time.... It actually is beginning to look like something other than a pile of parts....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/First%20Assembly_zpsqk0zrvsg.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/First%20Assembly_zpsqk0zrvsg.jpg.html)

The barrel and Monocoque tube are not in place in the photo, because I wanted you to be able to see the general arrangement of how the parts fit together.... It was great to actually be able to shoulder it and see how the ergonomics work.... I'm quite pleased, although the gun is definitely long.... The LOP as shown in the photo is 14".... I still have to machine the side holes for the valve screws, the hole on the left for the gauge, and the slot on the right for the cocking handle for the hammer.... Then it remains to machine the slot for the bolt handle in the Monocoque tube and the Breechblock.... The next time I put it together it should look close to the finished product.... Long, thin, and heavy....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Stikman on December 24, 2015, 02:52:56 AM
Ya know what...your rifle looks like a Ljutic "Spacegun". Cool...

(http://i622.photobucket.com/albums/tt301/weeb52/image_3.jpeg)[/URL]
Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on December 24, 2015, 09:32:42 AM
Looking very Nice Bob!!!!


Merry Christmas,

Matt
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on December 24, 2015, 10:51:01 AM
I have been reading with jaw on the ground in total amazement as to your skills and dedication to your projects.  I do a lot of modding to my air guns but its pale in comparison to the depths you go and accomplish in such a relatively short time.

I am in need of a lathe / mill and did not realize you can even get a attachment to do milling on a lathe as I do have a friend that has an old South Bend lathe of 48" by 8" swing I believe with a 1" thru hole I could get for a grand with more tooling and cutters than I would likely need but as has been said it not so much the money being the problem as the room required to set it up for use.

Keep up the good work and I will be following to the end when we get to see what the beast will do and hope you can ring the bell at 500 yards with her.

Mike
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 24, 2015, 01:14:12 PM
That's a great deal on the old (well equipped) South Bend, that's a big lathe for home use.... Check on eBay and see if you can find a Milling Attachment for it.... The one for my late 60's Atlas 6 x 12 cost me $400 in 2008.... The drawback is that they are not as rigid as a proper milling machine, have a small vice, limited vertical travel, and the horizontal travel is whatever the croosfeed travel is on the lathe....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on December 24, 2015, 04:56:01 PM
Bob
Yea the lathe is very appealing and is calling my name as my friend used it to do a lot of gun barrel work years ago but has since gotten up in the years and is not capable of using as much anymore. It is quite a bit more than we need in the modding of our air guns but then for the price with all his years of tooling bought to go with it makes it very tempting.

Just got to clean out the garage of clutter to make room for it and will look into the suggestion of Ebay for a milling attachment as its got to be more stable than my bench top drill press is and certainlu much safer to boot since a drill press is not really designed for milling.

Keep up the good work and eagerly waiting for the first shot to be heard around the world.

Mike
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 24, 2015, 08:38:35 PM
Today I had to figure out how the drill the side valve holes at exactly 90* and aligned with the top and bottom valve holes.... Normally I use a 5C collet in a 4-sided holder, but the maximum diameter collet is 1", and the tubes are 1.25".... In addition, they are 4 feet long, and difficult to handle when clamping in my short, 2.5"  wide milling attachment.... The trick is to make sure that the hole drilled through top to bottom is exactly vertical, ie square with the C/L of the chuck.... I got the idea to make a fixture that I can clamp in the chuck of the lathe with two 3/8" holes at exactly 90* to the chuck, that will straddle the diameter of the tube and allow me to put a 3/8" bar through the existing 3/8" holes in the tube.... I didn't have any metal tubing large enough, so I used a piece of 1-1/4" ID plastic pipe, mounted it in the milling attachment, and drilled a 3/8" hole straight through at 90* to the wall of the pipe, and exactly on the centerline.... It's crude, but it should work....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Tool_zpsapkxfan0.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Tool_zpsapkxfan0.jpg.html)

The next step is to make sure that when the tube is clamped in the milling attachment that the centerline of the tube lines up with the vertical centerline of the chuck.... I put the tube in the milling vise temporarily, and using an edge finder found the top of the tube.... It is then a simple matter to raise the vise up the radius of the edge finder (0.100") plus the radius of the tube (0.625") and the tube will then be vertically centered relative to the chuck....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Centering%20Tube_zpss7gi8ws4.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Centering%20Tube_zpss7gi8ws4.jpg.html)

Next I put the alignment tool in the chuck, lined the hole up roughly vertical, and put the tube loosely in the vice and lined the hole in the tube up with the holes in the tool....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Installing%20Tool_zpsoqt07exw.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Installing%20Tool_zpsoqt07exw.jpg.html)

Then I carefully slid a 3/8" diameter bar through the vertical hole, while rotating and sliding the tube around until the bar passed through all four holes.... and then I tightened up the vice, checking as I did so to make sure the rod would still slide easily....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Bar%20Through%20Tool_zpszpsxlgol.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Bar%20Through%20Tool_zpszpsxlgol.jpg.html)

At that point, I removed the tool from the lathe chuck, and checked the bar to make sure it was vertical relative to the ways of the lathe.... As you can see, it was....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Checking%20Vertical_zpsvndjwhsq.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Checking%20Vertical_zpsvndjwhsq.jpg.html)

The last set was to use the edge finder again to locate the center of the existing holes in the tube, so that when I drilled the side holes, they would line up perfectly....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Finding%20Hole%20Center_zps7z9lo0fe.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Finding%20Hole%20Center_zps7z9lo0fe.jpg.html)

This gives you an idea of what can be involved just in setting up to drill a hole accurately in a piece of tubing.... I'm pleased to say that it paid off, and the side holes ended up nearly perfectly aligned with the ones on the top and bottom of the tube.... One hole need a touch with a file on one side, and the other needed to be moved over about 0.005" with a Dremel on one side so that all four valve screws could be inserted and will take equal loads when the tube is pressurized.... When I can use the 5C collet in the square holder, I usually don't have to correct the holes at all, but this worked well, considering the multi-step setup required.... Once I had the cross hole drilled, I then used that, with a 3/8" pin in the chuck, to lay out the hole for the gauge in the left side, and the slot for the cocking handle in the right side.... Here is a photo of the top and left side....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Reservoir%20Tube%20Top_zps9i5f0krk.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Reservoir%20Tube%20Top_zps9i5f0krk.jpg.html)

and here is a photo of the bottom and right side of the reservoir tube.... You can see the hammer through the cocking slot and sear slot....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Reservoir%20Tube%20Bottom_zps0e8opt4c.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Reservoir%20Tube%20Bottom_zps0e8opt4c.jpg.html)

This was a time-consuming process to go through just to drill three holes and cut one slot.... but that's the way it goes when you have equipment with severe limitations like a milling attachment on a lathe.... You can usually do it, but figuring out HOW and getting set up is the hard part....  The back end of the Reservoir Tube is now complete, the only machining left to do on it is to cut it to length and drill the four holes in the front to bolt in the fill fitting....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on December 24, 2015, 10:20:28 PM
Glad the hole turned out the way you wanted. Like they say "Measure twice, cut once."
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 24, 2015, 10:21:58 PM
Only TWICE ?!?.... That must be what I'm doing wrong.... *LOL*....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on December 24, 2015, 10:23:53 PM
Only TWICE ?!?.... That must be what I'm doing wrong.... *LOL*....

Bob

LOL!!
Title: Re: .257 cal Monocoque PCP
Post by: Rizen 1 on December 25, 2015, 09:19:12 AM
Very nice Bob!!!  I am blown away at what you have done with such limited equipment!
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 25, 2015, 09:02:29 PM
Gee, guess what!?!.... I found a beautiful Millet 6-25 X 56 SF scope under the tree this morning!.... Things were quiet around here this afternoon, so I decided to cut the tubes to length and assemble the Monocoque PCP for the first time.... Here is what it looks like....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Monocoque%20PCP%20First%20Assembly_zps556zo3lu.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Monocoque%20PCP%20First%20Assembly_zps556zo3lu.jpg.html)

I still have to add the bolt, fill fittings and barrel stretcher, and it already weighs just over 13 lbs.... without the scope!.... It is 49.25" long, although it looks longer.... It does balance nicely, in the back half of the forestock....  Then I removed the buttplate, and installed the BiPod (actually a TriPod, I guess) and the scope.... I think it looks pretty awesome....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Monocoque%20PCP%20on%20BiPod_zpsdff5kkmo.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Monocoque%20PCP%20on%20BiPod_zpsdff5kkmo.jpg.html)

This is pretty much a bench gun, although it could certainly be used prone for varminting, using the BiPod and with or without the buttstock.... I really like the easy adjustability of the BiPod for height and tilt, using the handwheels.... It was a pretty cool Christmas present to put it together and look at it for the first time....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: YEMX on December 25, 2015, 10:01:13 PM
Ah!  Now I see what you mean by "monocoque"...  I had an idea like this a while back- of course, I'm still lacking the skills to bring something like this to life!  Well done Bob!!
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 25, 2015, 11:47:12 PM
Yes, the upper tube is the main structural member (in compression), holding the barrel in line via tension, and containing the breech, and the scope mounted on top.... As you can imagine, a 1-1/4" OD CrMoly tube is quite stiff.... The reservoir doesn't touch the Monocoque tube forward of the breech and scope, in fact it clears it by about 1/4".... The hope is that the barrel will act like a free-floating barrel that is 1-1/4" in diameter.... but without the weight associated with that.... The Belleville washers at the muzzle, when compressed, will put up to 1300 lbs. of tension on the barrel.... and if that isn't enough, I can double them up and double the force to over a ton.... Did you know that a properly torqued 1/2"-20 thread (45 ft.lb.) develops a axial load of 5400 lbs. (more if lubricated)?.... Threads are amazing !!!

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Job on December 26, 2015, 10:07:20 AM
Looks great  :o,when you're done, please make a video to see how it works. :-*
How much would the total cost to make one of these for sale?
Merry Christmas everyone
Title: Re: .257 cal Monocoque PCP
Post by: Rizen 1 on December 26, 2015, 10:11:37 AM
That is AWESOME!!!!  I love it Bob!   8)
Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on December 26, 2015, 10:45:45 AM
Looks awesome!!!
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 26, 2015, 01:22:31 PM
Total cost for a duplicate?.... see my comments at the top of page 6.... not going to happen....

I think this is probably the first of my builds I can truly call a "Custom" gun.... The only major parts, other than the scope and mounts, that I purchased are the barrel and trigger group.... Everything else (except for things like fasteners, etc.) was machined from steel or aluminum.... Oh, except for the level and pulleys for handwheels on the BiPod.... It's been a long time getting to this level, and I have to admit, it feels like a right of passage.... 8)

Bob
Title: Re: .257 cal Monocoque PCP
Post by: scottyhazzard on December 26, 2015, 02:25:48 PM
Perhaps, Bob, not so much a right of passage but an exercise demonstrating a mastery of every component of an extreme air rifle. The aeronautical components of the round it will fire. The deep understanding and mastery not just of the materials and engineering but also of the tools used to render metal into a distinct form with a focused purpose. It is really amazing. I can do none of these things but I understand some of what goes into each of these things. Each of these things on their own when mastered are impressive, all together is entirely something else. I appreciate humility but in this case I really think you might be shorting yourself or under appreciative of all the different fields of science required to accomplish the design just for someone else to build. Yet you built it yourself! This is closer to some sort of Zen. Just an amazing thing to follow along.
Title: Re: .257 cal Monocoque PCP
Post by: Motorhead on December 26, 2015, 03:19:03 PM
Well well ... see now this mass of parts & pieces has morphed into an actual Air Weapon ... (http://www.bmwlt.com/forums/images/smilies/av-101150.gif)


Going to be of interest "IF" the P-rod spec trigger group is upto task of holding the heavy hammer loads required to make this rifle fire at it's potential ?

Wild looking rig you have here Bob !!
Looking good  8) 8) 8)
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 26, 2015, 04:49:41 PM
Scott, the PRod trigger doesn't concern me in the least.... I already put the hammer against it and pushed MUCH harder than the 20 lbs. maximum force when cocked.... The sear engagement, which is between 0.030-0.040" with the hammer up solidly against the top inside of the tube, likewise is not an issue.... I am, however, using a square front on the hammer, with maybe a 0.005" radius on the edge, to reduce the vertical load on the sear when cocked.... The back of the sear has plenty of angle on it to kick it down out of the way when it fires.... Interestly, this gun is much easier to cock than some of my modded Discos, or my Hayabusas, because of the preloaded spring arrangement and long hammer travel of 1.5".... but I expect little or no hammer bounce because of the gap between the uncocked hammer and end of the guide, which takes about 7 lbs. to make it move at all because of the preload.... This gun is the smoothest, easiest cocking big bore I have ever had....
 
Today I drilled the holes in the front of the tubes for the retaining screws for the Fill Fitting and Barrel Tensioner....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Front%20Machining_zpshs8r52lo.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Front%20Machining_zpshs8r52lo.jpg.html)

Here is a photo of the muzzle, showing the recess for the Belleville washers and nut that will tension the barrel....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Recess%20for%20Bellevilles_zps6vzep38r.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Recess%20for%20Bellevilles_zps6vzep38r.jpg.html)

That completes the machining on the Reservoir tube.... All that remains on the Monocoque tube is the slot for the bolt handle....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on December 26, 2015, 04:52:54 PM
Will you be making your own bullets?



Never mind!! I see you will be using the Bob's Boattail bullet mold.
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 26, 2015, 05:21:27 PM
Yes, the tooling for the moulds is now being made at NOE, and I plan to get a mould for both the 113 gr. and 102 gr BBTs I designed for them.... I already cast my own bullets, and I have a .257 sizing die, so I should be ready once the moulds are done.... Here is what they will look like....

(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/257-100-FN_BT_102_gr_Sketch_zpsfkvdlxo3.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/257-100-FN_BT_102_gr_Sketch_zpsfkvdlxo3.jpg.html)  (http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/257-113-FN_BT_113_gr_Sketch_zpso7ulddpq.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/257-113-FN_BT_113_gr_Sketch_zpso7ulddpq.jpg.html)

I will need the actual bullets in hand before I can cut the chamber in the barrel to the proper length.... I have a chamber reamer that I made previously that is the correct size for this barrel, fortunately....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Bill G on December 26, 2015, 09:23:24 PM
Holy cow!  That 113gr javelin, is it about 1.05" long?
Title: Re: .257 cal Monocoque PCP
Post by: Bryan Heimann on December 26, 2015, 09:50:08 PM
Looks like a sweet rifle, perfect for long range varmint hunting.  Very exciting

Edit- i wouldn't be concerned with the weight.  A sniper rifle weighs around 16 pounds these days.  As long as you can keep it around 20 pounds or less, it will be fine to sling.  The advantage of not requiring a tether is worth it.  Keep a buddy bottle in a backpack to top up every few shots.  You'd be a fool to take those long shots on critters off-hand anyway.  I bet this gun will be rock solid and steady on a bipod.  Maybe put a smaller bipod with elevation screw in the rear, for that benched effect in the field.  Obviously not a woods gun, but on a big farm it would be so sweet...
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 26, 2015, 11:43:34 PM
113 gr. is 1.028" long (4 calibers), with a calculated BC of 0.400.... the 102 gr. is 0.900" long.... I also designed a 90 gr., which is 0.771" (3 calibers) long....

Bob
Title: Re: .257 cal Monocoque PCPu
Post by: MJP on December 27, 2015, 03:53:43 AM
It does look good, and I know the feeling when you get the very first one built that is truly yours.
All the planning and machining coming together as your own unique gun.

Marko
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 27, 2015, 08:11:24 PM
Yesterday and today I machined the J-slot for the bolt handle in both the Monocoque tube and the Breechblock.... I also installed a Velocity Adjuster that works by choking the barrel port by preventing the bolt handle from withdrawing fully into the lower part of the J-slot.... I consists of a 3/16" rod running in a milled slot, and a 10-32 screw to control the position of it.... In addition, there is a small set-screw which presses a plastic plug against the side of the adjusting screw to act as a brake to prevent it from moving by itself.... Here is the Breechblock, showing the J-slot, bolt handle, and adjuster.... In this photo, it is closed about 30% from wide open....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/J-slot%20Bolt%20With%20Power%20Adjuster_zpsmbslevjv.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/J-slot%20Bolt%20With%20Power%20Adjuster_zpsmbslevjv.jpg.html)

I'm very pleased with the positioning of the bolt handle and cocking handle.... I was a bit concerned that your hand might hit the bolt handle when cocking the gun, but I can wrap my big mitt around it no problem and my knuckle doesn't (quite) touch the bolt handle during cocking.... Here is a photo of the gun in the cocked position....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Monocoque%20PCP%20Cocked_zpsuj0aygdp.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Monocoque%20PCP%20Cocked_zpsuj0aygdp.jpg.html)

You can see that the bolt handle is fully back in the J-slot in that photo, which means that the nose of the bolt is completely clear of the barrel port.... Here is a photo of the gun unloaded, with the cocking handle forward (uncocked) and the breech open for loading.... There is lots of clearance between it and the scope....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Monocoque%20PCP%20Unloaded_zpshelm24rz.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Monocoque%20PCP%20Unloaded_zpshelm24rz.jpg.html)

I also made a brake for the hammer spring preload position adjuster today, to prevent that from adjusting itself as well.... This completes the major part of the machining on this project.... I can assemble everything now, except I am still waiting for the bolts to secure the Valve and Fill Fitting, so I can't as yet pressure test it.... I measured the reservoir today, and it is a whisker over 400 cc, not including the volume inside the valve, so I should have about 25 CI of air available.... If I can manage to tune for a shot string from 3800 psi down to 3000 (55 bar), that works out to 1375 CI, which would work out to about 7 shots at 200 FPE, if I can get the gun to produce 1 FPE/CI at that power level (which is likely a stretch).... I am more likely to tune it for tethered use at 3800 psi, and to get 3 shots within a very narrow ES off tether.... What the FPE level ends up when tuned like that.... is now the big question....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Bill G on December 27, 2015, 09:48:06 PM
Bob, I noticed that your length of pull is adjustable.  What is the range and what is you preference?

Bill G
Title: Re: .257 cal Monocoque PCP
Post by: Bryan Heimann on December 27, 2015, 11:30:41 PM
0.400 bc, in a small bore air rifle, is nuts.  If you could work it out to get 8 accurate shots in the ballpark of 200 fpe, it would be something else.  The extreme bench rest dudes should be beating down your door...
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 27, 2015, 11:40:24 PM
The LOP is adjustable from 13-15", I usually use around 14".... The drop from cheekpiece to shoulder pad is also adjustable, in six 1/4" increments, over a range of 1-1/4".... I can also twist the shoulder pad to any angle....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: LeadBreakfast on December 28, 2015, 01:54:10 AM
I cannot express how impressed I am with the entire process you have shown us, from design to follow through. Can't wait to see what she will do, I'm sure that the results will speak for themselves. Absolutely outstanding, Bob!
Title: Re: .257 cal Monocoque PCP
Post by: Bill G on December 28, 2015, 07:11:39 AM
The LOP is adjustable from 13-15", I usually use around 14".... The drop from cheekpiece to shoulder pad is also adjustable, in six 1/4" increments, over a range of 1-1/4".... I can also twist the shoulder pad to any angle....

Bob

Nice and versatile.  I too like about 14" lop.  I had not noticed the other two adjustments.  It looks like you are going to use fairly low mounts also.  Have you considered maybe making an adjustable elevation mount since this is going to be a long range rig.  Say some thing made to give 50 MOA per revolution.  Who knows, you might be the next 1000yr guy. At least it looks like it has long range written all over it, especially when we see those ICBM's you're planning to use for slugs LOL.  Very nice build indeed and pretty darned quick too.  Especially based on the equipment that you have discussed.  Goes to show you, CNC isn't always the answer.  That project would have take 30% longer if you would have written CNC programs.  One off is one off and a DRO will get you there faster than CNC IMO.  I'll be anxiously waiting on your results. 

Very  8)

BillG   
Title: Re: .257 cal Monocoque PCP
Post by: Bill G on December 28, 2015, 11:25:14 AM
Bob,  are you securing the end caps by way of threads or the screw head method?  if the screws, how do you determine how much web you need to a safe build?  Is there a formula that you employ? I think that I can do this method faster than threading.  Whats your preference?

Bill G
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 28, 2015, 04:18:13 PM
Bill.... There is 40 MOA machined into the Picatinny rail, which should put me on the paper at 200 yards with the scope near optical zero.... It has about 140 MOA of adjustment due to the 35mm tube, and the MilDots are calibrated at 25X.... so by just cranking up the Elevation and using the MilDots I should be good to 500 yards.... The scope came with rings, but they are very tall, so even with the sun shield and the angle on the scope rail the front of the scope clears the Monocoque tube by a wide margin....

What's a DRO ?!?.... I'm kidding, of course.... but my old Atlas and I still manage with handwheels and an edge-finder, thank you very much.... *LOL*.... I use a dial guage on the ways for carriage travel.... 1" of movement at a time, of course.... but for knowing how much of a pass you are making for milling, or how deep a hole you are drilling, that works OK....

The end caps (Valve and Fill Fitting) are secured with four 1/4"-28 SHCSs each, set 1/8" into the plug, so that the shear plane is above the root of the threads (even though that wasn't necessary).... Using the root diameter of the threads in the shear calculation, my safety margin is 4:1 at 3800 psi.... and the yield of the pockets in the tube on the heads is 2.7:1 (way more than the 2:1 required on that).... The tube hoop strength is 3.9:1 using UTS at that pressure, and all critical safety factors on the pressure vessel are above 3.5:1 at 4200 psi.... so in reality that is the MSWP I can use.... in fact even at 4500 psi they are well over 3:1....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 28, 2015, 05:40:59 PM
The tooling for the bullet moulds has been ordered from NOE.... therefore moulds for the 101 gr. and 112 gr. Bob's Boattails I need for this project should be available early in the New Year.... I'll keep you posted as to when they can be ordered, in case anyone else is interested.... Mike at TJ's reduced the land diameter of the barrel to 0.248" (the groove diameter is still 0.257") to make sure that the 7" twist rifling gets a good "bite" on the bullet.... so I reduced the mid-body of the bullets to 0.246" to make sure it doesn't touch the lands and cause additional drag....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on December 29, 2015, 12:58:51 PM
Bob

Very well thought and engineered project that has got to be begging to be tested and the fact that you now have to wait for the bullet molds to arrive just to start testing would be more than I could handle but then I am sure you still have plenty of little tweaks needing completed to keep you busy till the molds arrive. You say sometime in mid January we should see some testing numbers and just what all your hard work has produced. I am on the edge of my seat waiting to see how it shoots and if you obtain your goals envisioned for it.

Mike
Title: Re: .257 cal Monocoque PCP
Post by: Bill G on December 30, 2015, 12:13:56 PM
Bob

Very well thought and engineered project that has got to be begging to be tested and the fact that you now have to wait for the bullet molds to arrive just to start testing would be more than I could handle but then I am sure you still have plenty of little tweaks needing completed to keep you busy till the molds arrive. You say sometime in mid January we should see some testing numbers and just what all your hard work has produced. I am on the edge of my seat waiting to see how it shoots and if you obtain your goals envisioned for it.

Mike

Naaaah, waiting on molds isn't but a tick on the clock.  Waiting for spring, that would be maddening.  lol
Title: Re: .257 cal Monocoque PCP
Post by: Bill G on December 30, 2015, 12:28:18 PM
The built in 40 MOA is a good call for a gun that is intended for longer distances.  Its a lot less expensive and/or easier than building or buying a mount that will adjust.   

So you use a 2.7x thread root diameter to locate the head pocket from the end of the tube?  Did I misinterpret that? I've not used this method but once and it was on a design that used WAAAY less pressure than we discuss here.  Is this the hop strength calculation that you mentioned?

Bill G     
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 30, 2015, 04:03:56 PM
No, I meant that the load on the pockets in the tube has a 2.7:1 safety margin to the yield point of the CrMoly.... The screw heads load the tube wall, over an area equal to the diameter of the hole times the thickness of the tube.... That load, for pressure vessels, must be less than 2/3rd of the yield strength of the material (a safety margin of 1.5:1).... but I always use at least 2:1 so that the load is less than the fatigue zone of the steel.... That way, they are good for an infinite number of cycles.... The hoop strength (burst pressure of the tube) and the shear strength of the bolts are supposed to have a safety margin of 3.5:1 based on the ultimate tensile strength of the material (derated 60% for the bolts in shear).... Those criteria on my tube and bolts exceed 3.5:1 at 4200 psi, so that would be the approved MSWP of the reservoir....

The distance of the pocket from the end of the tube, for calculating the tearout strength, is based on the distance from the center of the hole to the end of the tube, times 2, because there are two shear planes, one on either side of the hole.... The holes locating the Fill Fitting are 2 hole diameters (0.75") from the end of the tube, and there are 4 holes, so the safety margin is about 9:1.... With that many screws, having the center of the hole only 1 diameter from the end of the tube would be plenty.... The rule of thumb is to have the center of the hole 1.5 diameters from the end of the tube (the side of the hole at least the diameter from the end).... but that only applies for a single screw.... and is still affected by the thickness of the tube.... It just gives a quick visual, if the hole is at least it's diameter from the end of the tube, it is probably far enough.... Better to do the math, IMO....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Airgun.Sniper on December 30, 2015, 04:12:05 PM
 I havent read evrything but thats pretty cool.
Title: Re: .257 cal Monocoque PCP
Post by: rkr on December 30, 2015, 04:33:51 PM
The tooling for the bullet moulds has been ordered from NOE.... therefore moulds for the 101 gr. and 112 gr. Bob's Boattails I need for this project should be available early in the New Year.... I'll keep you posted as to when they can be ordered, in case anyone else is interested.... Mike at TJ's reduced the land diameter of the barrel to 0.248" (the groove diameter is still 0.257") to make sure that the 7" twist rifling gets a good "bite" on the bullet.... so I reduced the mid-body of the bullets to 0.246" to make sure it doesn't touch the lands and cause additional drag....

Bob

In principle that means that .25 pellet noses should work as bore riding in those barrels. Dagn, I wish we could get those liners here in Europe as well.
Title: Re: .257 cal Monocoque PCP
Post by: Bill G on December 30, 2015, 09:22:34 PM
The tooling for the bullet moulds has been ordered from NOE.... therefore moulds for the 101 gr. and 112 gr. Bob's Boattails I need for this project should be available early in the New Year.... I'll keep you posted as to when they can be ordered, in case anyone else is interested.... Mike at TJ's reduced the land diameter of the barrel to 0.248" (the groove diameter is still 0.257") to make sure that the 7" twist rifling gets a good "bite" on the bullet.... so I reduced the mid-body of the bullets to 0.246" to make sure it doesn't touch the lands and cause additional drag....

Bob

In principle that means that .25 pellet noses should work as bore riding in those barrels. Dagn, I wish we could get those liners here in Europe as well.

I missed that completely.  The JSB's that I've measured are .250 at the head and .255-.258 at the skirt, depending on how rough the shipping was I suppose.  so, In theory, you could shoot pellets in that barrel also and expect a good result.  That might make a good universal barrel, especially in the reg 14 Twist.  interesting. 

You can probably get them but shipping would be out right financial molestation.

Bill G
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on December 31, 2015, 01:42:21 AM


Naaaah, waiting on molds isn't but a tick on the clock.  Waiting for spring, that would be maddening.  lol


[/quote]

Bill

Yea the waiting for winter to get over would be a real drag for sure and not sure where Bob is but down here in Dixie it was 77 degrees Christmas day and sunny so we have not even had a winter as of yet.

I would go mad waiting for the snow to melt just to shoot the new toy and I guess is why I live in Dixie as we don't usually have enough winter to worry about and definitely not enough to go mad waiting for spring to arrive.

Sweet home Alabama.

Mike
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 31, 2015, 02:20:08 AM
My range will clear of snow about April.... *LOL*.... and then the Motel will get busy by Mid-May.... so my shooting time will be VERY limited.... With luck I will get time to bust some Ground Squirrels with it in June....

bob
Title: Re: .257 cal Monocoque PCP
Post by: sixshootertexan on December 31, 2015, 11:41:08 AM
As usual great work Bob. I'm not seeing how the breech is secured in the tube. I know you have it somewhere so when you put the barrel in tension with the bellville washers.
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 31, 2015, 01:16:33 PM
There are two 10-32 screws, top and bottom, behind the loading port.... to keep it aligned.... Once all the other screws are in place (scope rail, the screws that fasten the upper and lower tubes together, etc. it isn't going anywhere.... Even just the mount for the cheekpiece on the back is probably enough to hold it (two 8-32 screws in tension)....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on January 01, 2016, 01:20:20 AM
My range will clear of snow about April.... *LOL*.... and then the Motel will get busy by Mid-May.... so my shooting time will be VERY limited.... With luck I will get time to bust some Ground Squirrels with it in June....

bob

I am glad you are apparently a patient person since I could not put the time and effort into such a project like your gun and have to wait till then to really see what it will do. You don't have any indoor ranges in the area that you can shoot it just to work any bugs out before the snow breaks so its ready to have fun with or will you just start a new project to stay busy till its time to shoot all the toys.

Mike
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on January 01, 2016, 01:29:46 AM
Yeah, I have a staggering 20 feet available in my garage/shop.... but that is good enough for testing and development.... Generally my guns are fully sorted before they ever get shot outdoors....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on January 01, 2016, 01:36:26 AM
I should have figured as much with the expertise you bring to the table that you have the bugs fixed before they get a chance to develop and 20 feet is still enough to shoot with a proper backstop for your cannons. LOL

Mike
Title: Re: .257 cal Monocoque PCP
Post by: OleTomCat on January 01, 2016, 03:46:44 AM
My range will clear of snow about April.... *LOL*.... and then the Motel will get busy by Mid-May.... so my shooting time will be VERY limited.... With luck I will get time to bust some Ground Squirrels with it in June....

bob

Bob,

Put it in a Box and send it to me, we have 70f and sunny here, I will be shooting at my outdoor range, up to 200 yards, this Saturday...

Al
Title: Re: .257 cal Monocoque PCP
Post by: lloyd-ss on January 01, 2016, 11:29:57 AM
Hi Bob,
I was just going to skim through this long thread but instead got hooked and read it all.  This is certainly a well thought out single purpose gun and I would be shocked if it didn't live up to the expectations.  I understand how everything has to be custom made, because what you can normally buy is close, but never quite right. I like the barrel tensioning with the belvilles. I might have missed it, but are the only attachment points for the barrel at the breech and the muzzle? I will be curious to see if you need to add any centering rings along the length of the barrel, or if the 2 attachment points get the job done.  With the belvilles, you can certainly put plenty of tension on the barrel and hopefully get the performance of a solid barrel.
Doing your milling with one hand behind your back is an understatement! I don't know how you get all the milling done with your set-up, but you obviously do.
It looks like like you are getting close on this one and we are all anxious to hear about the first shots.
Very nice project!
Lloyd
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on January 01, 2016, 12:10:07 PM
Lloyd, thanks for the kind words.... I've tried the Bellevilles before, and the concept works but my biggest problem is time to test at longer ranges as the Motel is always busy in the summer.... QVTom who builds the Slayer uses a tensioned barrel without the Bellevilles (they get in the way of using the shroud as an LDC), I think he torques the tensioner.... My idea (since we can't make guns quieter in Canada anyway) is to virtually eliminate temperature change as a problem by using the Belleviles to compensate, and to turn their compression distance into a tuning tool.... I don't have any intermediate supports at the moment, they can always be added later.... Tom found he was getting a nice musical note without them on firing, and added one.... My guess is now only dogs can hear the barrel on his gun singing to them.... *LOL*.... I figure if I need one, I will try it at 3/7ths of the distance between the supports to avoid a resonance point....

Some days I certainly feel like I am milling with one hand tied behind my back.... but somehow my stubbornness pays off in the end.... I really don't have a choice, do I?.... I'm certainly looking forward to getting the moulds from NOE, casting some bullets (in itself quite a development project), cutting the chamber, and the first test firing....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Bill G on January 01, 2016, 03:43:01 PM
Oh yea, I forgot about you still needing to cut the chamber.  Duh, that's why you are anxious to get the molds.   Job best done with a slug on hand.  The more I review this project the more I like your lines on this rig.  For me the simplistic look and straight forward function of design just hit the spot.  I've never been one who gets wrapped around beautiful wood and so on.  Its nice no doubt but its best left to fine furniture IMO.  In fact the design makes me think about what if's.  What if you were to use the tensioning shroud as a reservoir?  Do you think that it could or would have an adverse effect on the barrel dynamics?  since you have all the wasted volume that can't be used for hushing, why not use it to increase shot count?  That is, as long as it doesn't affect accuracy. :-\
Title: Re: .257 cal Monocoque PCP
Post by: Bill G on January 01, 2016, 03:45:58 PM
never mind..... that would make it not floating duh.
Title: Re: .257 cal Monocoque PCP
Post by: lloyd-ss on January 01, 2016, 04:34:32 PM
Bob,
BTW, very nice Christmas gift from your wife.  It is good when we get to the point in life where we can exchange gift "hints" and they work out 100%.
I am sure, being the gentleman you are, that she received something very special also.  But you don't have to tell us, LOL.
Lloyd
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on January 01, 2016, 04:57:39 PM
Using the shroud for a reservoir, while possible, would either make the gun even heavier (the upper tube is only 0.065" wall instead of 0.095").... and, as you say, I would likely fasten the tubes together full length.... I'm not so sure that would be a bad idea anyway, as the barrel being tensioned the way it is, isn't exactly floated anyway.... My guess is that changing the pressure in the reservoir would change the length of the reservoir enough to change the tension, even with the Bellevilles, however.... or at the very LEAST change the POI.... I'm  hoping by using the Monocoque tube idea, with the barrel, scope, and breechblock all inside it, will provide the maximum rigidity and least POI shift possible.... At one point I contemplated using aluminum or carbon fibre for the shroud Monocoque tube, and also using a carbon sleeve glued on the barrel, but was advised against it by michaelthomas (builder of the Thomas BR), to keep all the thermal coefficients the same between the scope and muzzle.... His guns are built not only to shoot amazing groups, but not have any POI change day to day, week to week, or under hugely varying conditions.... I took his advice....

Lloyd, that scope is MASSIVE, but it doesn't look at all out of place on this gun.... and yeah, she did OK.... *grin*.... We're at the stage in life Christmas and Birthday gifts are seldom a surprise any more, and often occur before the event.... "You want that, no problem, it's your Christmas present".... *LOL*....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: match on January 02, 2016, 05:10:47 PM
Note that using the shroud as a reservoir will put multiple stress effects on the tube so you would have a much lower burst/yield pressure and the force to buckling will also be reduced.

take a look at petrowiki.org/Strength_of_casing_and_tubing to see the details.

john
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on January 03, 2016, 09:08:29 PM
Lloyd, that scope is MASSIVE, but it doesn't look at all out of place on this gun.... and yeah, she did OK.... *grin*.... We're at the stage in life Christmas and Birthday gifts are seldom a surprise any more, and often occur before the event.... "You want that, no problem, it's your Christmas present".... *LOL*....

Bob
[/quote]

Bob
Same here with the better half as we ask/tell each other what we want/need for Bdays and Christmas since there are no secrets in a good marriage/partenership that last any amount of time. Besides I usually by what I want before she get the chance so have to save something for her to buy. Hehe

Mike
Title: Re: .257 cal Monocoque PCP
Post by: lloyd-ss on January 06, 2016, 08:56:21 AM
.................................................
Same here with the better half as we ask/tell each other what we want/need for Bdays and Christmas since there are no secrets in a good marriage/partenership that last any amount of time. Besides I usually by what I want before she get the chance so have to save something for her to buy. Hehe

Mike

My wife is happy for any suggestions so long as she can find it on line, LOL. I guess I am lucky that we are both pretty level headed about the money. But we each have our own weaknesses and respect that.
Lloyd
Title: Re: .257 cal Monocoque PCP
Post by: Bill G on January 09, 2016, 12:05:03 PM
Note that using the shroud as a reservoir will put multiple stress effects on the tube so you would have a much lower burst/yield pressure and the force to buckling will also be reduced.

take a look at petrowiki.org/Strength_of_casing_and_tubing to see the details.

john

Seals would likely be the weakest link.  but not reason to consider if repeatable accuracy is the goal.  the dynamics of a design of such would simply add variables and we don't need any more than that.
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on January 13, 2016, 03:39:18 PM
Finally got my valve screws, so I got to assemble the reservoir today and pressure test it.... Filled it 1K at a time, checking for leaks (none) and it's currently sitting at 3500 psi.... I'm topping off my Great White tank with the ShoeBox to complete the fill....

I slid the hammer down the tube, with it angled about 20*, and was rewarded with a nice loud POP and the valve sealed up again 100%, so things are looking good so far....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: lloyd-ss on January 13, 2016, 04:18:03 PM
Note that using the shroud as a reservoir will put multiple stress effects on the tube so you would have a much lower burst/yield pressure and the force to buckling will also be reduced.

take a look at petrowiki.org/Strength_of_casing_and_tubing to see the details.

john
John, Good information to think about if the tensioning tube was going to be used used as a reservoir, with the barrel as the hollow inside of the reservoir.  But if I read the info correctly, with the normal D/t diameter to wall ratio of gun barrels being 10 to 1 or lower, that puts them well within the 16 to 1 safe zone for likelihood of any yield (changing shape) from the reservoir pressure.  But just running some numbers, it looks like a .62" tube with .065 wall with a 70ksi yield is safe to over 14000 psi before deformation is likely to start. 
With the small  L/D ratio of the shroud, and the fairly light end compression loading of maybe 1000 pounds max, it looks like buckling is not a concern, either.  Still, it is good to be aware of all relevant failure modes.
Lloyd
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on January 13, 2016, 04:27:19 PM
Lloyd, if you pressurized the Monocoque tube, to use it as a reservoir (and of course it would need the same 0.095" wall thickness as the main reservoir).... would that not remove any compression load from it completely, and instead put it in tension?.... Instead of about 1000 lbs. of compression, I see it as having over 3300 lbs. of tension at my 3800 psi working pressure.... If you loaded the barrel to 1000 lbs. of tension, relative to the outer tube, the outer tube couldn't have any bucklng because it would still be in about 2300 lbs. of tension.... You are just transferring some of the load on the end cap to the barrel instead of the tube....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on January 13, 2016, 05:47:18 PM
It's now sitting at 4500 psi, no leaks I can find, so I'll leave it for a week and see what happens....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: lloyd-ss on January 13, 2016, 05:54:17 PM
Lloyd, if you pressurized the Monocoque tube, to use it as a reservoir (and of course it would need the same 0.095" wall thickness as the main reservoir).... would that not remove any compression load from it completely, and instead put it in tension?.... Instead of about 1000 lbs. of compression, I see it as having over 3300 lbs. of tension at my 3800 psi working pressure.... If you loaded the barrel to 1000 lbs. of tension, relative to the outer tube, the outer tube couldn't have any bucklng because it would still be in about 2300 lbs. of tension.... You are just transferring some of the load on the end cap to the barrel instead of the tube....

Bob
Bob, I am not sure that the math is that straightforward, and I think that was John's concern. Still, I think we are working with rather low levels of loading  (except for hoop stress) with the various tubes, and are ok.
Lloyd



You are now pressurized to 4500psi and you are going to let it sit for an entire week?  :o   Either you have an awful lot of patience, or you are just waiting for some more parts to arrive anyway.  ;)
Lloyd
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on January 13, 2016, 07:18:46 PM
I can't cut the chamber until I get some bullets.... ATM, the tooling to make the moulds is still being made.... next the moulds.... then I have to cast some bullets.... I'm guessing at least another month before I get to shoot it for the first time....  ::)

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on January 13, 2016, 09:07:43 PM


My wife is happy for any suggestions so long as she can find it on line, LOL. I guess I am lucky that we are both pretty level headed about the money. But we each have our own weaknesses and respect that.
Lloyd
[/quote]

Lloyd
Mine is about the same way as long as I can find it online for her. LOL We also are both pretty good with our money but also have our weakness and respect as well and I thinks that what makes it last as a partnership.

By the way just as a side note I will let you know the tubes you made me for my 2240 Hipac project are working out very nicely and used quite often. I fill them to 2200 psi and get 25 and 20 shots per gun with the 16 and 14 inch tubes using JSB 10.34s shooting at 875 to 895 fps. Thank you very much for taking on the project for me about a year ago, it took awhile to get them built as my health decided to get in the way for a bit but got that controlled so its back to having fun.

Thanks again and take care.

Mike
Title: Re: .257 cal Monocoque PCP
Post by: William on January 13, 2016, 09:22:18 PM
I can't cut the chamber until I get some bullets.... ATM, the tooling to make the moulds is still being made.... next the moulds.... then I have to cast some bullets.... I'm guessing at least another month before I get to shoot it for the first time....  ::)

Bob

Oh no, I'm not sure I can stand another month, this is going to drive me crazy lol

Bob,
Congratulations on your build, it sure is getting close to testing that's for sure. Well I guess a month isn't too long!!!!

William
Title: Re: .257 cal Monocoque PCP
Post by: lloyd-ss on January 14, 2016, 10:41:26 AM


My wife is happy for any suggestions so long as she can find it on line, LOL. I guess I am lucky that we are both pretty level headed about the money. But we each have our own weaknesses and respect that.
Lloyd
==============

Lloyd
Mine is about the same way as long as I can find it online for her. LOL We also are both pretty good with our money but also have our weakness and respect as well and I thinks that what makes it last as a partnership.

By the way just as a side note I will let you know the tubes you made me for my 2240 Hipac project are working out very nicely and used quite often. I fill them to 2200 psi and get 25 and 20 shots per gun with the 16 and 14 inch tubes using JSB 10.34s shooting at 875 to 895 fps. Thank you very much for taking on the project for me about a year ago, it took awhile to get them built as my health decided to get in the way for a bit but got that controlled so its back to having fun.

Thanks again and take care.

Mike


Mike, Glad those replacement HiPac adapters and tubes worked out for you.  I don't know if you noticed the pictures of your broken HiPac adapter (the one I broke for you, ha, ha) in the thread about the unfortunate incident with a modified 22xx and HiPac adapter.  I think you dodged a bullet on yours.
Lloyd
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on January 14, 2016, 11:00:38 AM

By the way just as a side note I will let you know the tubes you made me for my 2240 Hipac project are working out very nicely and used quite often. I fill them to 2200 psi and get 25 and 20 shots per gun with the 16 and 14 inch tubes using JSB 10.34s shooting at 875 to 895 fps. Thank you very much for taking on the project for me about a year ago, it took awhile to get them built as my health decided to get in the way for a bit but got that controlled so its back to having fun.

Thanks again and take care.

Mike


Mike, Glad those replacement HiPac adapters and tubes worked out for you.  I don't know if you noticed the pictures of your broken HiPac adapter (the one I broke for you, ha, ha) in the thread about the unfortunate incident with a modified 22xx and HiPac adapter.  I think you dodged a bullet on yours.
Lloyd

Lloyd
No I missed the post and pics of the broken HiPac adapter other than the ones you sent me of mine that you saved me from experiencing failure with the hard way. We had discussed the observed short comings that I felt was inherent with the products and I am glad you agreed to make new ones for me as I do rest easier knowing that my safety is not at risk when enjoying my guns.

I do agree that I am a lucky soul since we both know what little force it took to break that one of mine with no internal forces being applied to help it fail. if you can find the link to the post on the failure I would like to read it or just the title wording and I can look it up myself.

Here is some pictures of the 16 inch tube gun completed when it was still in the tuning stages. 

Mike
Title: Re: .257 cal Monocoque PCP
Post by: lloyd-ss on January 14, 2016, 11:16:29 AM
Mike, PM sent.
Lloyd
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on January 14, 2016, 06:19:49 PM
Mike, PM sent.
Lloyd

Lloyd

Got it "WOW"

Mike
Title: Re: .257 cal Monocoque PCP
Post by: Bill G on January 16, 2016, 09:11:25 PM
oooooh too exciting Bob.  I can't wait to see the chony results. 

Bill
Title: Re: .257 cal Monocoque PCP
Post by: Jr_Explorer on January 19, 2016, 10:25:04 PM

Bob...  You just developed a revolutionary, quantum leap in airgun technology with the SSG.  Are you going to Disneyland?

"No  I'm going to build from SCRATCH an anti-satelite airgun to use on coyotes at a billion yards.  In my spare time.  Using nothing but some paperclips and duct tape."

I hate you.  I love you.  You go Bob!  LOL!

Seriously...  Thanks for everything you contribute here.  We're not worthy.  We're not worthy.
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on January 25, 2016, 08:17:17 AM
Bob
Any more progress on the 257 made yet like getting your bullet  mold's and casting bullets.

Mike
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on January 25, 2016, 12:41:40 PM
The tooling for the moulds is nearly done, so it won't be long before the moulds will be available....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on January 25, 2016, 02:43:30 PM
Un uh patiently waiting for the first shot from it
Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on April 08, 2016, 12:03:44 PM
How is this project going Bob?
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on April 08, 2016, 07:35:55 PM
Still waiting on the moulds.... and impatiently waiting for the first shot which I hope will follow in short order after that....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on April 08, 2016, 07:47:28 PM
Still waiting on the moulds.... and impatiently waiting for the first shot which I hope will follow in short order after that....

Bob

Hope they get to you soon!!
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on April 08, 2016, 08:50:24 PM
Still waiting on the moulds.... and impatiently waiting for the first shot which I hope will follow in short order after that....

Bob

Hope they get to you soon!!

+2

Mike
Title: Re: .257 cal Monocoque PCP
Post by: LeadBreakfast on July 02, 2016, 04:29:13 AM
Bob,
Followed this thread intently from the start, but I've been away for a couple of months. Have you had any progress with the molds and/or testing your new project?
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on July 02, 2016, 12:34:29 PM
I'm still waiting for a chamber reamer, and our Motel is in the busy season now.... I doubt I will get back to this until the Fall.... I do have the moulds for the 100 gr. and have bullets now, however....

(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/NOE%20Mould_zpsn8gsprsl.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/NOE%20Mould_zpsn8gsprsl.jpg.html)

(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/257%20cal%20100%20gr%20BBTs_zpssh8d3rzo.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/257%20cal%20100%20gr%20BBTs_zpssh8d3rzo.jpg.html)


(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/257%20cal%20100%20gr%20BBT_zpss0jqq9cz.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/257%20cal%20100%20gr%20BBT_zpss0jqq9cz.jpg.html)

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rifle50 on July 03, 2016, 02:00:01 AM
I'm still waiting for a chamber reamer, and our Motel is in the busy season now.... I doubt I will get back to this until the Fall.... I do have the moulds for the 100 gr. and have bullets now, however....

(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/NOE%20Mould_zpsn8gsprsl.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/NOE%20Mould_zpsn8gsprsl.jpg.html)

(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/257%20cal%20100%20gr%20BBTs_zpssh8d3rzo.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/257%20cal%20100%20gr%20BBTs_zpssh8d3rzo.jpg.html)


(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/257%20cal%20100%20gr%20BBT_zpss0jqq9cz.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/257%20cal%20100%20gr%20BBT_zpss0jqq9cz.jpg.html)

Bob

BOB, What is UP???? Your post above does NOT COMPUTE? On page 7 of this thread from Dec of 2015 you say THIS

Quote--"Yes, the tooling for the moulds is now being made at NOE, and I plan to get a mould for both the 113 gr. and 102 gr BBTs I designed for them.... I already cast my own bullets, and I have a .257 sizing die, so I should be ready once the moulds are done.... Here is what they will look like...."

("I will need the actual bullets in hand before I can cut the chamber in the barrel to the proper length.... I have a chamber reamer that I made previously that is the correct size for this barrel, fortunately...."")

Bob
Last Edit: December 26, 2015, 05:23:55 PM by rsterne

Then in this thread near top of page 10 from Jan 13, you say this
 
Quote-"I can't cut the chamber until I get some bullets.... ATM, the tooling to make the moulds is still being made.... next the moulds.... then I have to cast some bullets.... I'm guessing at least another month before I get to shoot it for the first time...." 

Bob

I am a simple man Bob, but I read you were awaiting molds originally to naturally chamber  specifically for, and already had a reamer that you had made previously, then you get the molds and cast bullets and posted pics of said bullets. No information since and your reasoning now is, awaiting a chamber reamer, that was posted you had already, and is the CORRECT SIZE FOR THIS BARREL????? And was weeks before Motel season??? In my mind it just doesn't compute? Or I am  really confused here?

Carl

Title: Re: .257 cal Monocoque PCP
Post by: rsterne on July 03, 2016, 02:13:30 AM
Yeah, I do have a reamer here, that I made myself a couple of years ago for another gun, but it's pretty crude.... I ordered another one over a year ago and I thought I was never going to get it, but the guy who is making it contacted me just about the time I got the mould for the 100 gr. bullets, and I figured I would wait for him to supply it.... That didn't happen before the Motel got busy, and I still haven't got it.... So now I won't have time to do much anyway until the fall, so I may as well wait for the new reamer.... If I don't have it by the time I can work on the gun, I will be forced to use the one I already have.... Make sense now?....  ::)

I appreciate your eagerness, rest assured I'm not dragging my heels because I want to.... I just want to do the best job possible, I think you can understand that?....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rifle50 on July 03, 2016, 02:19:15 AM
Yeah, I do have a reamer here, that I made myself a couple of years ago for another gun, but it's pretty crude.... I ordered another one over a year ago and I thought I was never going to get it, but the guy who is making it contacted me just about the time I got the mould for the 100 gr. bullets, and I figured I would wait for him to supply it.... That didn't happen before the Motel got busy, and I still haven't got it.... So now I won't have time to do much anyway until the fall, so I may as well wait for the new reamer.... If I don't have it by the time I can work on the gun, I will be forced to use the one I already have.... Make sense now?....  ::)

I appreciate your eagerness, rest assured I'm not dragging my heels because I want to.... I just want to do the best job possible, I think you can understand that?....

Bob

Thanks for the enlightenment.......Definitely understand doing the best possible.............Carl
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on July 03, 2016, 02:21:02 AM
In addition, there is a possibility that NOE may eventually figure out how to make the tooling to do the 112 gr. bullets, and I would really like to cut a chamber to fit both.... I'm hoping that will all come together this fall....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 11, 2016, 02:00:14 PM
Just a note here, to bring everyone up to date.... I couple of months ago I received a mould for the 112 gr. BBT.... I have still not received the chamber reamer I ordered from Sean Pero, and I can't contact him, so I may well have to either use the crude reamer I have, or make another one.... While waiting for winter to roll around and have some shop time, I ordered two more moulds from NOE (one each, 101 gr. and 112 gr.) and had them sent to Erik at Hollowpoint Mould Services for conversion to HP.... This will involve pushing the nose back on both bullet to a 50% Meplat for the 1/8" HP pins, and the weights for the HP versions will be about 97 gr. and 107 gr., possibly a bit less depending on the cavity size that Erik can achieve.... My wife ordered these for me for Christmas, bless her heart.... At the moment I only have a 0.257" sizing die, but will be ordering bushings from NOE to fit their sizer a couple of thou either side of that.... so that I can play with bullet diameter as well....

The plan is to get this rifle to the point of firing it this winter, so that I can at least see if it works, and assess the FPE limits at various pressures.... I still have to make another inline regulator set for 3600-3800 psi for tethering, depending on the pressure required to drive the bullets at suitable velocities.... Early in the spring I will be building a new "semi-portable" shooting bench that I can transport in my new Defender SxS.... so I hopefully will have a shooting setup worthy of the gun.... I still have my fingers crossed that I may be able to take my first Varmints with it in 2017.... Wish me luck !!!

Bob
Title: Re: .257 cal Monocoque PCP
Post by: William on December 11, 2016, 02:33:28 PM
Thats some good news, even though it has been delayed a little!  Just praying your reamer or one you may have to make works well.  Sounds like to me that you may very well be shooting some varmints early this spring or when the weather permits!

Sure wish you had that reamer :-[
Don't worry your plans will come together, you seem to have a way with making things happen  :D

Anyway Bob,

To you as well as your family and friends,

Merry Christmas to you all, God Bless

William & Family
Title: Re: .257 cal Monocoque PCP
Post by: Tofazfou on December 11, 2016, 03:18:27 PM
Bob,

Can't you get custom reamers from McMaster Carr?  I think Doug gets his reamers from there to do my airguns.  He just ordered a special size and i think McMaster is where it came from.  And it got there in less that 2 days.  Could be wrong about McMaster.  Just not worthy to be waiting this long for a reamer
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 11, 2016, 04:41:21 PM
McMaster Carr won't ship to Canada.... I would seriously doubt they make chamber reamers, with a pilot, tapered leade, and chamber all in one.... but I could be mistaken.... never thought to ask.... It didn't really matter once the reamer wasn't here by May, I was dead in the water for shop time until November anyway....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: dyotat100 on December 11, 2016, 05:24:08 PM
They don't have tapered reamers. I use straight reamer and then use a tapered stone file to make the taper. I always ream it smaller and use 400 to make it perfect.

Can't have a real tapered reamer for every caliber.

I do have 2 257, 2 308 and a 338 with 1 degree taper.  257 is .25680" and then I use 400 to polish the straight to hand fit a sized slug for the condors.

Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 11, 2016, 05:32:35 PM
The reamer I was waiting for is like the one I have for my 7mm....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Reamer%20and%20Thimble_zpszjf2hdom.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Reamer%20and%20Thimble_zpszjf2hdom.jpg.html)

I have made similar ones myself, but only with a single cutting edge.... They work OK, but I prefer Sean's (above)....

(http://i378.photobucket.com/albums/oo221/rsterne/Millenium%20Pumper/IMG_2872.jpg) (http://s378.photobucket.com/user/rsterne/media/Millenium%20Pumper/IMG_2872.jpg.html)

Both reamers cut the tapered leade and the parallel chamber in one operation.... You vary the depth to suit the longest bullet you want to use, just as you would doing it by hand....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: dyotat100 on December 11, 2016, 05:46:08 PM
Yes I have 6 flute carbide chamber reamers. They have a 1 degree taper on them and have a pin on the front for a guide  bushing.

Tom found this guy and he makes them exactly the size you ask for. I always have them made .0002" under bore size so I can make sure I get a nice fit for the condors. Not having a bolt I make them so they push in and won't fall back if you point the gun straight up.

I have to get one made for the 7mm. It was a expensive barrel and worth having a $130 reamer made.
Title: Re: .257 cal Monocoque PCP
Post by: Tofazfou on December 11, 2016, 07:26:18 PM
Cool Bob.  I see.

Just wanting to help.  After reading your updates, I thought about Doug and his reamers and figured i would try and pass along the info if it helped.

Eagerly awaiting your build results.....

Tofazfou
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on December 11, 2016, 09:21:00 PM
Bob
Thanks for the update on the monocoque as I knew the last time I asked you said you were still waiting on the moulds I thought but I see know you got those and are waiting on the reamer to finish the project. Hopefully you will get some word on the reamers or find another source so you don't have to use your homemade one if possible.

Thanks for responding to my inquiry and keep us up to date on this cool project.

Mike
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 15, 2016, 07:43:32 PM
I finally got around to casting some of the 113 gr. bullets today....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/NOE%20257%20cal%20113%20gr_zpsepq1ol4r.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/NOE%20257%20cal%20113%20gr_zpsepq1ol4r.jpg.html)

By comparision, here are the 100 gr. which I did a while back....

(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/257%20cal%20100%20gr%20BBT_zpss0jqq9cz.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/257%20cal%20100%20gr%20BBT_zpss0jqq9cz.jpg.html)

The 113 gr. is pretty much a scaled down .308 Whiteout (which was 200 gr.).... The chamber will be cut to accommodate both....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Tofazfou on December 15, 2016, 09:58:58 PM
Oh man, my trigger finger is seriously itching.  For scientific purposes ;), i would love to try a handful of those to see if they would work in my TD.  Just for shucks and giggles of course.  I'm curious about them as i love the design.
Title: Re: .257 cal Monocoque PCP
Post by: lloyd-ss on December 16, 2016, 01:04:46 AM
Bob,
I've got a nice reamer like in the top pic in reply #208  .2475/.2590.  I am pretty sure it was made by Sean. Looks like his work.
Also have the same type of reamer for the .30 cal TJ's barrels, .293/.301.
Lloyd
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 16, 2016, 01:27:46 AM
Lloyd, I may end up borrowing that .257 cal.... I also have one of Sean's in .30 cal just like yours....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: dyotat100 on December 16, 2016, 01:44:53 AM
What does your barrel slug?

.259" is .002" larger then the bullets I shoot in my TJ barrel.

Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 16, 2016, 02:19:01 AM
I would have to check it again.... IIRC it's 0.248" land and 0.257" groove, with a 7" twist.... How big do you make your chambers, Doug, relative to the groove diameter?.... I find that even if you try to make the reamer dead on, it always cuts a couple of thou larger....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: dyotat100 on December 16, 2016, 02:39:36 AM
I make it so the bullet I'm shooting fits snug. I have 2 reamers. One is .25660" and the other is .25680". They cut pretty much what they are. I also use a floating reamer holder from PTG.

Then I take 400 grit paper on a rod and polish it till I get the perfect fit.

I used a piece of peek push on the pin and then machine it to size on the reamer.

The floating reamer let's the ream line up perfect with the bore.

Here are 2 257, a 308 and 338
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 16, 2016, 12:26:10 PM
Nice!.... I have a LOT to learn about barrel prep, thanks !!!

Bob
Title: Re: .257 cal Monocoque PCP
Post by: dyotat100 on December 16, 2016, 01:03:09 PM
Because the AF guns don't have a bolt the leade in has to be pretty much perfect. To loose and the bullet will fall back in the breech. To tight and you can't get it in with your finger. 

That's why I get under sized reamers. Can always open up but can't put it back. The leade is cut for longest bullet.

If you want to use the .257 reamer your welcome to.

I'm hoping the 338 leade is deep enough. I have a 185 gr mold on its way. Never thought I would be shooting that bip of a bullet. I did a test and it is going to work good as long as the bullet is a shooter. Should be because it's just a upscale of what I shoot now
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on December 16, 2016, 01:33:56 PM
Thanks for the offer, Doug.... My plan is to make a .217 cal reamer for my Disco Double today.... If that goes well, I will make my own for the Monocoque.... I'll let you know if I need to borrow one....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Erik Green on February 09, 2017, 09:51:29 PM
Hello Bob;
I am thinking of building a similar rifle to you monocoque in your .308 BBT.  Would like to base it on the TJ's 1-10 twist .308 liner.  Saw you posting on the NOE site re: BBT bullets twist etc. but would appreciate you input on feasibility.   Like you I want to try for MOA at 300yds.  Practical, or would I be ahead to go with .257? Do not want to commission a custom barrel.
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on February 09, 2017, 10:10:53 PM
What you are looking for is certainly possible.... You don't state what barrel length or pressure you may use, and these have a direct relationship on the weight of bullet (SD) that you can drive to a given velocity.... I went into quite a bit of detail on that in my thread on the NOE Forum, to try and help shooters pick a bullet weight, and then corresponding twist rate....  http://noebulletmolds.com/smf/index.php/topic,1137.0.html (http://noebulletmolds.com/smf/index.php/topic,1137.0.html) .... For instance, at 3000 psi in a 24" barrel, if you want about 950 fps, you need to stay to an SD of about 0.17, which in .308 cal is about 115 gr.... On the other hand, at 4000 psi in a 30" barrel, you could go to an SD as high as 0.27 and get a similar velocity.... which would allow you to use up to a 180 gr. bullet.... My 113 gr. BBT will work in a 17" twist, while the 176 gr. needs a 10".... There are three weights currently in the NOE Store, the 135 gr. 155 gr. and 176 gr., all available at.... http://noebulletmolds.com/NV/index.php?cPath=374_378 (http://noebulletmolds.com/NV/index.php?cPath=374_378)

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Voltar1 on February 12, 2017, 05:13:30 AM
Hi Bob, curious where you are at with this rifle build?
Love to hear more of it eh!!
Walter
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on February 12, 2017, 02:07:26 PM
I now have the bullets cast, and sizing dies are here.... I'm just finishing up another project (my BRod builds) and this is next on the list.... I'm tired of waiting for Sean Pero to make my chamber reamers, so I'm going to make my own.... Once I get the chamber cut so that both the 101 gr. and 112 gr. BBTs will chamber properly, it will be time for the final assembly and first tests.... I'm really looking forward to it !!!

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on February 28, 2017, 12:38:42 AM
Well, I finally got back to working on this project.... The reservoir was empty, I had a very slight leak in one of the O-rings (there are only two in the reservoir), so since it was empty I took the opportunity to pull it apart and replace the 70D O-rings with 90D.... It has been sitting at 4000 psi for 24 hours, so I guess I cured the leak.... I measured the land and groove diameter, finished up my reamer drawing, and today I made the chamber reamer.... I'm very pleased with the way it came out.... Each time I do one of these, it gets just a little nicer and more accurate....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/257%20Monocoque%20Chamber%20Reamer_zpsj1ordmct.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/257%20Monocoque%20Chamber%20Reamer_zpsj1ordmct.jpg.html)

I used a three flute design, like the one I did a couple of months ago for my .22 cal Regulated Disco Double.... It is machined from a piece of 3/8" O1 Drill Rod, hardened, and then polished, and tempered in my wife's oven at 465*F for an hour.... While it was baking I did a bit more reading on tempering, and discovered that it is the thickness of the transparent oxide layer on the polished surface that causes the colour.... It starts at yellow, through dark straw, brown, purple, blue, then a lighter blue, as the temperature is increased.... I was aiming for a dark straw to brown colour, which is about 490*F.... Once the oven was up to temperature, after about 10 minutes, it looked just right, but I decided to let it heat soak for an hour, and it darkened to brown with a few purple spots.... I was a bit worried that I had gone too far, but apparently even though the part isn't getting hotter, the oxide layer gets thicker with time.... One recommendation I found was to use 1 hour per inch of thickness of the part, so I really don't need to heat it for as long as I did.... If anything, it might be a little tougher, and not quite as hard, but I think it will cut just fine....

For those of you not familiar with chamber reamers, the part on the left, with no cutting flutes, is the pilot that guides the reamer by running on the lands.... The reamer is then necked down a bit, and has a 1 degree taper for about half the length of the flutes, and then a parallel section to cut the chamber.... I make my chambers about 0.001" over the groove diameter.... It then steps down again at the end of the flutes.... The only part that really does any cutting is the last half of the taper and the first part of the chamber.... You just keep running it deeper into the barrel until the chamber is the length you need for your bullets.... I will be cutting the chamber on my Monocoque to fit both the 100 gr. and 113 gr. BBTs, which means it will also fit the 98 gr. and 109 gr. HP versions.... I have sized a bunch of them (both lengths) to use for checking the chamber depth, most to 0.257", but a few to 0.256" and 0.258" just so I can judge the fit.... The aim is to have the nose of the shorter bullet starting into the leade, but not have the longer one too difficult to chamber.... 113 gr. on the left, 100 gr. on the right....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/NOE%20257%20cal%20113%20gr_zpsepq1ol4r.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/NOE%20257%20cal%20113%20gr_zpsepq1ol4r.jpg.html)  (http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/257%20cal%20100%20gr%20BBT_zpss0jqq9cz.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/257%20cal%20100%20gr%20BBT_zpss0jqq9cz.jpg.html)

It's really nice to get back to work on this project after a year of waiting for bullet moulds and a chamber reamer (which never arrived).... It won't be long and I will be able to test fire it for the first time....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on February 28, 2017, 01:16:49 AM
I am sure it was very frustrating to be so close to being able to take the first shot yet not having the last two pieces of the puzzle to complete the build. Gald to see you have it back in the works for completion and test firing for the first time.

Mike
Title: Re: .257 cal Monocoque PCP
Post by: MJP on February 28, 2017, 02:22:14 AM
Looking good, was a bit worried when I saw the color of the reamer. Did you use hss drill rod, I usually do use hss without hardening, fast and easy to make with carbide tools.
Looking forward for finally seeing some test shots on your rifle.

Marko
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on February 28, 2017, 02:54:25 AM
I used "oil hardening" O1 Drill Rod.... Easy to machine before hardening.... Heat bright cherry red and quench in oil (I use Canola oil), then polish back up before tempering in an oven.... If you rub bar soap on the reamer before heating with the torch it prevents that black scale from forming.... The grey oxide coat polishes off quite easily.... Its glass hard before you temper it.... but really brittle.... According to the info I have, the difference in hardness going from dark straw to purple-brown is less than one Rockwell number.... but the colour it is should be a lot tougher....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: MJP on February 28, 2017, 08:29:36 AM
Ok, now I understand, cos I usually use hss it's much simple to do one off tools. And my mill is so rigid it does cut it really easy with tungsten carbide cutters.
Do you sharpen the cutting edges with oil stone?

Marko
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on February 28, 2017, 12:33:10 PM
I use a very fine diamond file to just hone the flute where the end of the mill cut it, both before hardening and after tempering.... I don't touch the outside of the reamer the rake is created when you plunge the end mill 0.012" past the centerline (I use 4-5% of the caliber).... The outside is polished before hardening by sanding with 400 grit rotating the reamer in reverse to remove any burrs from milling.... The reverse rotating insures you don't round the cutting edge (if you don't push too hard on the sandpaper).... After hardening I polish the outside lengthwise with 600 grit before tempering....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Reamer_zpsywtq5w0p.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Reamer_zpsywtq5w0p.jpg.html)

That is the basic cross section of my reamers.... dimensions are in calibers.... The dotted line is the way I make a single flute reamer.... This view is from the tailstock....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: MJP on February 28, 2017, 01:09:46 PM
I usually go little bit more past the centerline to get better relief on the back and more rake, but don't know if it really matters doing a cutter for one or two uses.
Everybody makes things little different and endup pretty much the same result I quess. It's like programming cnc, you can tell at the shop who made what program, everyone has their own fingerprint pattern on the programs.

Marko
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on February 28, 2017, 11:35:44 PM
The further you plunge the mill past the centerline, the faster the reamer will cut, but generally not as smooth, and also more load on it.... I'm never in a hurry....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on March 02, 2017, 08:43:44 PM
Yesterday I reamed the chamber, and arrived at a length where the shorter bullet stopped against the leade about 1/16" before being chambered fully, and the long bullet was about 3/32" from being chambered.... This meant you could just feel slight resistance on the bolt handle to chamber the 100 gr., and a slight push to chamber the 113 gr.... That was the last bit of machining I had to do, other than machine the transfer port to final length.... This morning I gave a final lapping to the crown, and then polished the bore with JB Bore Paste, followed by Bore Brite, cleaned the gunk out of the bore, and the gun was ready to assemble and test fire for the first time.... That happened this afternoon, nearly a year later than I had hoped....

My Great White was at 4000 psi, which was about where I hope to run the gun, so I just tethered it and ran the initial tests.... I used the lightest and heaviest bullets I will be using, the 98 gr. HP version of the 3.5 caliber long BBT, and the 113 gr. FN version of the 4.0 caliber long BBT.... With the velocity adjuster bottomed out I couldn't quite cock the gun, but with it backed off 1/2 turn the gun would cock fine, and the cocking effort was still quite reasonable.... This gun has a separate cocking handle on the hammer, all the bolt does is load the bullet into the chamber.... There are so many things different about this build, although I had high hopes, I really didn't know if they would be realized.... It was with those very mixed emotions I pulled the trigger for the first time.... and was rewarded with a velocity of over 1000 fps.... I did the typical testing I always do with a new gun, find out where the maximum is (the velocity plateau) and then work back from there.... I then changed to the heavier bullet, and worked my way back up to maximum.... I only shot 1 or 2 bullets at each 1/2 turn preload adjustment, and then plotted the curves, as shown below....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Monocoque%20Initial_zpsf0qe0mus.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Monocoque%20Initial_zpsf0qe0mus.jpg.html)

The maximum velocity is reached  at this pressure with 1.5 turns of adjustment left with the heaviest bullet, and 2 turns left with the lightest one.... The peak performance was 1003 fps (219 FPE) with the 98 gr. bullet, and 950 fps (227 FPE) with the 113 gr.... This is basically right what I had hoped for, what I really didn't know was the pressure it would take to achieve those numbers.... Now I know it takes 4000 psi.... I shot a few more rounds, and did a bit of playing around to see what I could get for a shot string.... I'm not interested in detuning this gun for a long string, the gun will primarily be shot tethered to a regulator, and tuned for a short (3-5 shot) string off reg.... Tuning in this way keeps the efficiency reasonable, and yet enables you to disconnect for a short string if necessary.... Once the tank was down to 3800 psi, and I had a rough idea of where to adjust the preload to get a short string, I shot the following off reg....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Monocoque%201st%20Off%20Tether_zpsny5hxqif.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Monocoque%201st%20Off%20Tether_zpsny5hxqif.jpg.html)

That is 4 shots, averaging 928 fps (209 FPE) within a 14 fps ES (1.5%).... The pressure started at 3790 psi and ended at 3320 psi, and the reservoir on the Monocoque is 24.7 CI (405 cc), so that works out to an efficiency of 1.04 FPE/CI.... Let me tell you, it's about twice as loud on the 4th shot as on the first, so when tethered it will be quite a bit better than that four shot untethered average.... Now that I know the gun is a success, I can work on the last piece I need.... an inline regulator that I can adjust from 3000-4000 psi by changing the shims.... That will allow me to fine tune the velocity sweet spot with the pressure, while setting the hammer spring reload to give me that 3-5 shots off tether that I desire....

During this build, I had a lot of negative comments about the 7" twist being too fast, that it would prevent me from ever achieving my goal.... and the rifling being too deep (it's 0.001" deeper than a normal .257 barrel), which would likewise ruin the performance.... I think these initial results should be enough to put the nay-sayers to rest.... I'm just grinning from ear to ear that I achieved my goal, without having to exceed 4000 psi....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Gippeto on March 02, 2017, 09:11:15 PM
Very cool Bob. 8)

Congrats!

Al
Title: Re: .257 cal Monocoque PCP
Post by: Matt15 on March 02, 2017, 09:46:54 PM
Congrats!! I hope you get to do some long range shooting soon!  ;)
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on March 02, 2017, 09:53:31 PM
The plan is to have it ready for Gopher season in the spring.... It is a relief to see I haven't been spinning my wheels for nothing....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on March 03, 2017, 02:14:25 AM
That's some very well deserved performance from the build and I can see that ear to ear grin on your face for sure. I am just amazed at the precision that you put into your builds and reminds me of the hot rod days of my past where every little detail was never overlooked in that search for every last little ounce of go power.

Cant wait to see the accuracy out of it as I am sure it will be the gophers worst nightmare.

Mike
Title: Re: .257 cal Monocoque PCP
Post by: MJP on March 03, 2017, 02:50:10 AM
Nice Bob, really happy for you. Will be interesting to see how she groups.

Marko
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on March 04, 2017, 02:25:42 AM
Today, I took apart a Ninja 4500 psi "high-pressure" regulator and rebuilt it for inline use.... It looks like these other ones I have done previoulsly....

(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/Inline%20Regulators_zpslt17enpy.jpg) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/Inline%20Regulators_zpslt17enpy.jpg.html)

The modifications I made are as follows.... Do this only if you are competent working around HPA, and at your own risk.... Other regulator brands (or clones) may not be acceptable/safe when doing these modifications.... although if rated at 4500 psi input, and properly engineered to withstand a failure to that pressure, they should be....

1. Completely disassemble the regulator, removing both burst discs, the male Foster and the gauge from the reg. body.
2. Cut off the threaded stem that screws into the tank just below the safety vent hole.
3. Drill the bottom of the body to 11/32" until you just touch the three cross holes that pass air to the fill, gauge, and HP burst disc, and tap 1/8"-27 NPT.
4. Deburr and use compressed air to blow all debris and chips out of the regulator body, and install a plug, using Teflon tape to seal it.
5. Reinstall the male Foster (with NO check valve) and gauge, and install burst discs of the appropriate rating for the inlet and outlet pressures.
6. Remove the pin valve from the bonnet, and drill through 11/32" and tap 18"-27 NPT.  Remove all debris and chips with compressed air.
7. Install a female Foster in the bonnet.  I used a close hex nipple because I didn't have a female Foster with male threads.  Both Fosters should be rated for 4500 psi.
8. Install new O-rings on the regulator piston.  I would recommend using a Ninja rebuild kit from Mac1 Airguns, which comes with 90D Mil-Spec Urethane O-rings.
9. Install a Belleville washer stack appropriate to the pressure range you need, with appropriate shims, on the piston.
10. Install the piston in the reg. body and screw on the bonnet.
11. On the output side, attach an accurate gauge equipped with a bleed valve to the female Foster.
12. Fill slowly through the male Foster using a tank or pump, to 1000 psi, and check for leaks.  Repair if necessary.
13. Slowly increase the pressure at the inlet, while watching the gauge.  If you increase the pressure too close to the rating of the outlet burst disk it will fail.
14. If the burst disc fails, change your shorts, then change the disc, reduce the shimming in the regulator, and repeat.
15. If the indicated output pressure is too low, shut off the tank, bleed the system, and increase the thickness of the shims. If too high, remove shims.
16. When you have the regulator adjusted to the setpoint you want, "burp" the bleed valve a few times to settle the needle, and the reg. and double check the pressure.
17. Once you have the regulator adjusted the way you want, close the tank valve, and bleed the system.  Record your Belleville stack and shims for future reference.
18. You can now tether your gun to the output side of the regulator with a HP hose, and when you turn on your tank, your gun will fill to the setpoint pressure.
19. If your gun has a pressure gauge, fill slowly and double check that its gauge is close to what you read on your quality gauge.  They may not agree exactly.
20. Enjoy shooting you gun tethered to your tank.  Ideally, the burst disc on the output side of the regulator should be close to, or only slightly above, the MSWP of your PCP, in case the regulator fails.

Although you have to change shims to alter the regulator setpoint, this makes a great inline regulator at far lower cost than the $300 plus adjustable variety....  The regulator for my Monocoque is set at 3800 psi.... This required a very unusual Belleville stack to achieve that high output pressure, consisting of five pairs of Bellevilles, with each pair consisting of a 0.047" nested inside a 0.032".... and then two thick Ninja 0.020" (red) shims, arranged like this....  The flat shims are inside the regulator body, with the opposite end of the stack against the large end of the piston....

| | ) ) ( ( ) ) ( ( ) )

There are two BIG warnings about using this setup.... There is very little total travel, only 0.060" from loose to fully collapsed.... The pairs of Bellevilles take a huge amount of force to drive them flat, about 860 lbs., and that only takes 0.012" of movement per pair.... This means that EVERY 0.001" of shims changes the output pressure by about 90 psi.... Just a few thou of shims can make the regulator go from 3000 psi to not regulating at all, and passing the full tank pressure through to the output.... Most Belleville stacks are not this harsh to adjust, but when you need to go to high pressures, they get very fussy.... My regulator has a steel bonnet, I don't know if the aluminum bonnets found on some regulators are strong enough.... but Ninja sell "high pressure" regulators with the output set as high as 3000 psi, and having a 5K burst disc on the output side.... If they failed, they would pass the 4500 psi tank pressure through to the output side, and I trust Ninja to know what they are doing.... so I personally have no problem with such a high setpoint.... but I am NOT recommending that you do the same.... nor do I know if "clones" are engineered to the same standards, even if rated at 4500 psi.... as many do not have high enough output pressures to require a 5K output burst disc.... and only come with a 3K.... Substituting a higher rated output side burst disc may be pushing the safety of any regulator not so designed....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on March 04, 2017, 02:47:39 AM
Bob
I have found that when adjusting the output pressure on my Ninja regs used with my 13ci tanks on the QBs that I get a increase of 50 psi for every .005" shim I install. I am only going to a max of 1500 psi so I am just wondering when you say a increase of 90 psi for every .001" shim is that because you are setting at a much higher pressure.

Mine are the Ninja pro SHP regs if that makes any difference also.

mike
Title: Re: .257 cal Monocoque PCP
Post by: MJP on March 04, 2017, 02:53:05 AM
Bob you should have added a warning, do not ever try this with the generic Chinese eBay or any cheapo knockoffs out there!

Marko
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on March 04, 2017, 03:57:56 PM
Mike, it is because the "paired" Bellevilles are so stiff, and the total compression only 0.060" that makes the pressure very sensitive to shimming....

Marko, I did state Ninja regulators, but I added a warning about that, thank you....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: Michael Loar on March 06, 2017, 01:07:14 AM
Bob
Ok that makes sense and some of the bellevilles are .047s and .032s whereas mine are .032s and .023s in the lower pressure regs. So I can see how it would be more sensitive and react with a greater change in pressure.

Mike
Title: Re: .257 cal Monocoque PCP
Post by: MJP on March 29, 2017, 02:43:54 AM
Bob, when are we going to see some long distance groups?
I have been following this from the start and groups would be interesting.

Marko
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on March 29, 2017, 03:27:08 PM
The snow is melting fast here, Marco.... I am "aiming" for sometime next month for initial tests.... Cross your fingers....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: YEMX on April 16, 2017, 10:41:17 PM
(Please correct me and PM if I'm wrong, not trying to thread-jack)

Which Ninja Reg are you using, I'm seeing two on fleabay: Standard 4500 psi adjustable, the V2 4500 (NOT SLP).  For uh, scientific purposes...  ;D 

And uh, what would the stack look like for say... 2800 psi output?
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on April 16, 2017, 11:32:10 PM
Use the Ninja high-pressure reg (the one with the gold body, and 4500 psi input).... the same as the one they use in their 90 CI 4500 psi HPA fill stations to fill PCPs up to 3000 psi.... You can buy then from Ninja already adjusted in 200 psi increments, up to 3000 psi (ie 2600, 2800, 3000).... Most of the Belleville stacks for that pressure consist of the 0.047" (thickest) Bellevilles in series, either 8 or 9 or them, and some flat shims.... arranged like this....

| | ) ( ) ( ) ( ) (

If you use 9, the additional one would be on the right, like this.... ) .... against the piston.... the flat shims are against the reg. body....

9 of the 0.047" barely fit inside the Ninja regulator without any shims, and are nearly flat (ie think of coil bound for a spring) at about 2900 (plus/minus 100) psi, so not much adjustment.... You are probably better to use 8 and a stack of shims to get more adjustment range....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: YEMX on April 18, 2017, 10:27:03 AM
Excellent!! As always, thank you Bob, for the info!!
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on May 10, 2017, 07:40:37 PM
Well, a year after this project came to a grinding halt, I finally got a day to take her out and let her stretch her legs a bit.... I built a new shooting bench, and the Monocoque was the first gun to try it out at 100 yards.... Here is a pic of the setup....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Monocoque%20and%20Bench_zpsexah1ggx.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Monocoque%20and%20Bench_zpsexah1ggx.jpg.html)

and here is a photo of the range, currently set up for 100 yards....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/100%20yd%20Range_zpsmbaqexg6.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/100%20yd%20Range_zpsmbaqexg6.jpg.html)

The field I am set up in has the ability for me to move the bench back to 300 yards, or pretty much anything in between.... The rancher I shoot Varmints for allows me to leave the bench and target stand in his field.... I have wind flags on stakes, currently at 25, 50, and 75 yards.... and recently purchased an anemometer that I keep on the bench with me....

The Monocoque was tethered to my Great White by a 3800 psi regulator, and I shot enough to use 1000 psi from the tank today.... I had 12 different bullets to try, or rather 4 different bullets, and three diameters of each, 0.256", 0.257", and 0.258".... The bullets were the HP and FN versions of my two heaviest Bob's Boattails from NOE.... The bullets tested were a 98 gr. HP, a 100 gr. FN, a 109 gr. HP, and an 113 gr. FN.... All bullets were cast in 2% tin....

The Millet scope is mounted on a Picatinny rail that I milled to angle the scope downwards, to hopefully center the POI at 100 yards with the scope centered, and it worked perfectly.... I was within 4" at 100 yards, and only need to tweak the turrets a bit to roughly center me with the 109 gr. bullets.... The 113 gr. were a bit low, and the 98 and 100 gr. were a few inches high, because there is an 80 fps difference between the lightest bullet, at 960 fps, and the heaviest, at 880 fps.... The first targets were 3 shots groups, intended just to prove that the POI was intended, and one of those was the best group of the day....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Monocoque%20100%20yd001_zpsikrnqru2.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Monocoque%20100%20yd001_zpsikrnqru2.jpg.html)

I saw a pretty clear trend, with the heavier bullets begin more accurate, and the smallest diameter the least accurate.... I'm not thrilled with the average 5-shot groups I shot today, but that 3-shot above, at 1.12", show that the gun has promise.... One thing is clear, the holes in the target are perfectly round, showing no sign of yaw, so the 7" twist is sufficient even for the longest bullets....

Bob
Title: Re: .257 cal Monocoque PCP
Post by: MJP on May 11, 2017, 02:12:07 AM
Well you finally got to shoot her.
The tight twist is going to be interesting to find the perfect bullet and pressure combination.
Gun looks awesome for sure!

Marko
Title: Re: .257 cal Monocoque PCP
Post by: MJP on November 26, 2017, 04:33:55 AM
Hi Bob, digging this old thread up. Have you shot her more and found the working combination?
Would be nice to see more testing, if it will group or not?

Marko
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on November 26, 2017, 01:27:26 PM
Marko, your frustration at my lack of time to shoot pales by comparison to my frustration.... As soon as spring comes and the snow melts on the range, our Motel gets busy and I have to be here.... There are really no days off during tourist season (we are open 7 days a week, only my wife and I to run the place), which goes until mid-November, when the snow hits again.... My shop time is from then until April, but my summer shooting time is scarce.... The good news is that we will be closing the Motel in about 3 years, so the summer of 2021 I plan to spend a LOT of time shooting all the project guns that have been piling up from each winter's work.... I never thought I would have so little time to shoot, but at least there is light at the end of the tunnel now....

The only shooting the Monocoque got I reported above.... and that was really just proof of concept.... yeah it works!.... I have four bullet weights to try (2 FN and 2 HP).... and the sizing dies to go from a couple thou under bore diameter to a couple thou over.... In addition, I have the barrel tension adjustment to play with.... and of course I can adjust the velocity also.... so there is almost an infinite combination of factors to sort through to find the accuracy I hope is lurking there.... Indeed, the "Impossible just takes a little bit longer to achieve."....  ::)

Thanks for your interest.... it does help to motivate....  8)

Bob
Title: Re: .257 cal Monocoque PCP
Post by: bigben11 on January 06, 2018, 06:42:42 PM
I am looking to remove my air rifle pressure gauge(don't need it).  Is there anything available that I can use that has the same thread that can close that opening?

Does any one know what the standard thread size is on gauges.
Title: Re: .257 cal Monocoque PCP
Post by: rsterne on January 06, 2018, 08:39:15 PM
Most PCP gauges are 1/8"-27 NPT, so a standard pipe plug should work.... However, if your gauge is sealed with an O-ring instead of Teflon thread tape, it is likely a straight thread.... I would suggest checking the pitch with a thread gauge to make sure it is 27 TPI and tapered before just winding a pipe plug in the hole....

Bob