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Author Topic: .257 cal Monocoque PCP  (Read 54054 times))

Offline rsterne

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.257 cal Monocoque PCP
« 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.... 



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....



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) 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
« Last Edit: November 15, 2015, 01:29:19 PM by rsterne »
  • Coalmont, BC, Canada
🇺🇦 Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! 🇺🇦

Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline Motorhead

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Re: .257 cal Monotube PCP
« Reply #1 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  ;)
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Offline Monkeydad1969

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Re: .257 cal Monotube PCP
« Reply #2 on: November 11, 2015, 08:59:01 PM »
Man, Bob...You're definitely in BEAST MODE now!
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Offline dcorvino

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Re: .257 cal Monotube PCP
« Reply #3 on: November 11, 2015, 09:25:12 PM »
Very nice project Bob.
Look forward to reading about your progress.

Dave
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Offline Matt15

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Re: .257 cal Monotube PCP
« Reply #4 on: November 11, 2015, 10:38:36 PM »
Looks very cool Bob!!!  8) 8)
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Offline Monkeydad1969

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Re: .257 cal Monotube PCP
« Reply #5 on: November 11, 2015, 10:56:15 PM »
Can you go into detail about the valve setup?
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Offline rsterne

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Re: .257 cal Monotube PCP
« Reply #6 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....



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....



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....



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
« Last Edit: November 12, 2015, 12:32:20 AM by rsterne »
  • Coalmont, BC, Canada
🇺🇦 Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! 🇺🇦

Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline YEMX

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Re: .257 cal Monotube PCP
« Reply #7 on: November 11, 2015, 11:25:35 PM »
I can't wait to see the progress!!!! 
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Offline Prouzy

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Re: .257 cal Monotube PCP
« Reply #8 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.

Offline Gippeto

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Re: .257 cal Monotube PCP
« Reply #9 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?
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Offline rsterne

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Re: .257 cal Monotube PCP
« Reply #10 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
« Last Edit: November 12, 2015, 01:09:40 AM by rsterne »
  • Coalmont, BC, Canada
🇺🇦 Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! 🇺🇦

Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline Tofazfou

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Re: .257 cal Monotube PCP
« Reply #11 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
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Offline Tofazfou

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Re: .257 cal Monotube PCP
« Reply #12 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.... 



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....



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) 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!
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Offline Gippeto

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Re: .257 cal Monotube PCP
« Reply #13 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


You using something different to calc it?

Al
  • Alberta, Canada

Offline rsterne

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Re: .257 cal Monotube PCP
« Reply #14 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

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....
« Last Edit: November 12, 2015, 03:06:01 AM by rsterne »
  • Coalmont, BC, Canada
🇺🇦 Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! 🇺🇦

Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline Gippeto

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Re: .257 cal Monotube PCP
« Reply #15 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





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Offline dyotat100

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Re: .257 cal Monotube PCP
« Reply #16 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

« Last Edit: November 12, 2015, 08:55:51 AM by dyotat100 »

Offline rsterne

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Re: .257 cal Monotube PCP
« Reply #17 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
« Last Edit: November 12, 2015, 12:07:28 PM by rsterne »
  • Coalmont, BC, Canada
🇺🇦 Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! 🇺🇦

Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline Gippeto

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Re: .257 cal Monotube PCP
« Reply #18 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. ;)








  • Alberta, Canada

Offline Bill G

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Re: .257 cal Monotube PCP
« Reply #19 on: November 12, 2015, 05:07:53 PM »
This will be very interesting with 1:7 twist.  My eye is on this one.
  • Nicholasville KY
Engineering is the art of modeling materials we don't wholly understand, into shapes we can't precisely analyze, so as to withstand forces we can't properly asses, in such a way that the public has no reason to suspect the extent of our ignorance.