My Version of the Millenium Pumper

[rsterne]

A short while ago I built a .25 cal Carbine Pumper based on a shortened Disco Tube, the linkage from a Benji 392, and an MRod barrel.... While working on it, I started collecting ideas and parts for a rifle version using a full length Disco tube and a .25 cal choked Lothar Walther barrel.... Instead of having an auxilliary reservoir made from a 16 gr. CO2 bulb under the main tube, this gun would have an internal reservoir and a separate check valve.... After about a week in the shop, here are the main internal parts....



The pump linkage is an extended Billet linkage from Mac1 Airguns.... It is stronger, and 3" longer than stock, although it maintains the same 7.6" stroke, giving a swept volume in the Disco tube of 54 cc.... I wanted to mount the pivot pin as far forward as possible, so instead of shortening the Disco tube I made a threaded end plug to help spread the end load of the pivot pin into the tube.... The smaller stub on the front will mount a barrel band.... The piston is the same as the one I made for the Carbine.... Immediately behind that is a check valve, sealed both sides with O-rings, mounted into two new holes in the Disco tube and secured with high tensile 8-32 low profile SHCSs.... There is a 2.5" long, full diameter, (18cc) air chamber between the check valve and the extended front end on the valve.... The valve extension is 3/8" ID for most of its length, providing additional volume, and enough wall thickness to mount the gauge and a male Foster fitting on the left side just behind the gauge location.... That will enable the gun to be filled from a tank or stirrup pump, both easier than the onboard pump, whose main purpose is for topping up in the field.... Also shown is an MRod trigger with Challenger trigger guard.... Everything will be mounted in a inletted Boyd's Blaster stock from Norm at Discos-R-Us in Nutmeg laminate....



In the second photo are details of some of the parts.... The front plug was pretty tricky to machine.... I had to turn and thread it, mount it in the already slotted Disco tube, and then machine the slot and drill the pivot hole in the proper orientation.... It worked out beautifully, and the tube is full wall thickness at the pin location.... Below that is the check valve.... It is a simple aluminum housing, drilled through, and carrying a shortened check valve pin from a male Foster fitting, retained by a piano wire pin.... I tried one in my Carbine and it functioned perfectly, and the thin pin diameter left room for the screws on both sides.... Beside the check valve is the valve poppet and spring.... You can see how I have streamlined the head of the poppet, and narrowed the stem behind it.... The front of the valve spring has been expanded to 9/32" ID, to match the spring seat ID in the extended valve front end, for additional flow.... The brass part is a custom gauge mount I made from brass pipe fittings.... I used a 1/8" male to 3/8" female adapter and a 3/8" male to 1/8" female, then bored them out for additional volume, and threaded them together and sealed it with solder.... The Blaster stock is plenty deep enough for that assembly, and it added over 3 cc more volume to the valve.... The total volume is now 28.5 cc, slightly bigger than the Carbine was.... The Disco valve has been bored out inside to 0.62" ID, the throat drilled to 0.25", and the exhaust port milled out to 0.203" on a 20 degree angle.... It still needs a little TLC with a Dremel to round and smooth the inside corner.... The porting is 16% larger in area than what I used in the Carbine.... That combined with the longer barrel and slightly larger valve volume should gain a bit of velocity.... I'm hoping for about 10% higher FPE in this version at the same pressures.... With the additional leverage of the extended linkage, the effort should be the same at about 1800 psi as it was at 1500 in the Carbine.... so I have little doubt the peak power of this rifle will be higher....

This project resulted from my joining the Green Forum because of interest in their "Millenium Pumper" project, the concept of which was to bring MSPs into the 21st Century.... There was no concensus of opinion over what it should be like, so I undertook this project as my own interpretation of what could be done easily, starting with mostly Crosman parts and adding a few custom bits into the mix.... There are lots of other interpretations of the idea possible.... this just represents mine....

Bob

[longhunter]

it never ceases to amaze me the talent that some people possess. i can't wait to see the finished rifle.

[Wheelman88]

IMPRESSIVE!!Can't wait ts see the final results.

[rsterne]

Well, it holds air!.... I got the main tube assembly done and pressured tested to 2000 psi.... I can actually still use the pump at that pressure, and it doesn't seem much harder to pump than the Carbine at 1500.... which means hard, but not impossible....



I made and installed the hammer and the RVA, lengthened the rear of the bolt slot in the breech 0.10", faced 0.030" off the back of the valve and shortened the valve stem about 1/16" so that it is flush with the back of the valve when the valve spring goes coil bound.... Those modifications, along with the changes I made to the cocking slot in the tube and the bolt allow the maximum possible hammer travel, which works out to about 0.8".... No matter how the travel is adjusted, the cocking pin can't hit anything....

There are basically two areas left to work on.... The Lothar Walther barrel has to be machined to fit into the breech, I have to make a chambering reamer and cut the chamber and a groove for the O-ring, make a .25 cal bolt, machine the transfer port and crown, and make a barrel band.... On the Boyd's Blaster stock, I have to cut a hole for the gauge and relieve a few spots for the MRod trigger.... and then the major job of converting the forestock into the pump handle.... The stock will then need final sanding an finishing.... I'm really looking forward to seeing how this new pumper will perform....

Bob

[bradyman1]

You like those pumpers don't ya. Beautiful job. I can't wait to see how we'll it performs. No doubt it will be a hammer.

[QVTom]

Bob, your project is progressing nicely.  Your interpretation has taken the pumper to new heights and pressures with beautiful workmanship and engineering.  Be careful, you're are dangerously close to building every part of your gun!

Tom

[rsterne]

or at least REBUILDING it.... *LOL*....

Bob

[rsterne]

I completed the barrel work today.... I made a chambering reamer from O1 Drill Rod, hardened and tempered it, and then used it to cut the chamber to just past the transfer port location.... I then machined in the barrel port and a rebate in the end for the O-ring to seal the bolt.... It will be pinched between the barrel and the breech.... The barrel OD was reduced to 7/16" to fit the Crosman steel breech....



The reamer has a 0.246" pilot that just rides on the lands in the LW barrel.... It has a 2* taper to create the leade, and then the chamber is 0.254".... The chamber is machined to just past the front of the transfer port, with the leade in front of that.... I also did a target crown on the muzzle....



The barrel port is 0.188" wide by 0.219" long at the bore, tapering to a 0.204" circle where it mates to the transfer port, which will be made from a piece of 5/16" Teflon rod.... After finishing the machining, I used JB Bore Paste to lap the bore and the chamber, followed by a polish with their polishing compound.... The results are a mirror finish inside.... LW sure do make a beautiful barrel....

Bob

[Motorhead]

Looking really nice there Bob !!

[QVTom]

Excellent workmanship!

Nice reamer.  Do you use by hand or chuck super slow?

beautiful crown too.  It looks a lot like crown on the RainStorm  but with and addition of a counter bore.  Is that for protection or does it serve some other function?

Tom



Tom

[SciGuy]

That is some excellent barrel work.  Nicely done.

[rsterne]

I used 164 RPM but the lube was still smoking.... so next time I'll engage the back gear and drop it under 100.... You can change the aggresiveness of the reamer by how far past the centerline you maching the cutting edge.... On center it barely rubs off material, I used about 0.005" below to give a bit of rake to the cutting edge.... I've been told ~0.020" is the maximum.... Sometimes when you harden the reamer it warps a fraction and the "following" edge shades the cutting edge and it won't cut.... If that is the case, you just grind a bit off the corner of the following edge.... It can speed up the cutting dramatically.... in this case, I had so little material to remove it wasn't an issue.... After oil hardening, I tempered the reamer in an oven at 470*F for 30 minutes.... hence the nice dark straw colour....

The crown is at 90* to the bore, so the gasses can expand immediately without affecting the base of the bullet.... The disadvantage is that it is prone to damage, and that is the reason for the raised edge, to protect it.... I used to do all my crowns at 11*, but if you think about it, unless you indicate on the bore, even at that shallow angle you could have the crown closer to the breech on one side than the other, allowing the gasses to escape (a fraction) earlier on one side, possibly tipping the base of the bullet.... With a 90* to the bore, even if the bore is not concentric in the lathe, the release point for the gasses at the edge is the same all the way around.... Besides, it looks cool.... *grin*.... and it's actually easier....

Bob

[QVTom]

Yes, the in-your-face rifling is cool looking for sure and the fist detail I noticed.  You read so much from BR shooters about this or that angle and wonder how they can quantify such small changes.  The 90deg. makes perfect sense to me.

Thanks for the reamer tips, I was planning on single pointing my leade (advantage of CNC) but I think the reamer a will give better surface finish and require less cleanup.

Tom

[rsterne]

I got the main fitting of the stock done today.... When I ordered the Boyd's Blaster stock from Norm at Discos-R-Us I wasn't sure what I was going to use it for, so I had it inletted for a Disco without gauge.... I had to modify the inletting slightly for the MRod trigger, and I used a 1" Forstner bit to drill the gauge hole.... I also had to grind a small groove in the top left side to accomodate the Foster QD fitting.... The Challenger trigger guard came too close to my fingers on the pistol grip, so I had to shorten it a bit.... Fortunately, it doesn't have a "back end" so that wasn't a problem.... I've cut off the forearm off to make the pump handle, but haven't cut the groove yet for the pump linkage....



The other thing on today's agenda was to make the barrel bands.... The front one (right in the photo) fits on the 5/8" stub on the front of the front pivot block, so the outside of the band is the same diameter as the OD of the main tube.... The rear barrel band is designed to sit immediately in front of the gauge, and clamp the front of the breech in place for extra stability....



The Crosman steel breech's main weakness is the 4-48 screw in the loading port.... There is nothing forward of that to hold the breech and barrel in place.... I would have had the band right up against the front of the breech, but because of my oversized gauge mount I had to have a 1/4" gap between the band and the breech.... The band is made in two parts, the lower one will stay on the main tube, located with a set screw.... The upper half will sit on the barrel, just in front of the breech.... You remove the two clamping screws to remove the barrel and breech from the gun.... When you replace the breech and tighten the screws, it pulls down on the barrel, clamping the front of the breech securely against the main tube.... The top of the barrel band is flush with the top of the breech....

The only major jobs left are to cut the slot in the forearm for the pump linkage and make the .25 cal extended probe bolt.... With a little luck I'll get those done tomorrow and then I can give the stock a final sanding and start finishing it with Watco Danish Oil.... This thing isn't far from initial testing.... I just need Lloyd's MRod trigger shim....

Bob

[PakProtector]

Hubba-hubba!!!!!

drools...
cheers,
Douglas

[gene_sc]

Absolutely outstanding Bob.
Gene

[rsterne]

I tethered my "Millenium Pumper" today, running it regulated at 2000 psi to find out what it can do.... How does over 1000 fps with JSB 25.4 gr. Kings sound (over 57FPE) ?.... I initially set the hammer travel plunger flush with the end of the hammer, which gives me a travel of about 0.6", roughly the same as a stock Disco.... I can increase the travel 5 turns (24 TPI) or about 0.2" from there.... I ran through the entire range of RVA travel from coil bind out 12 turns (16 TPI) which is 0.75" of preload adjustment.... I then increased the travel 3 turns (0.125") and repeated the procedure.... Here are the results....



First comment is that coil bind occurs 2 turns further out on the RVA with the additional 1/8" of hammer travel, which makes perfect sense.... I noticed that at high preload the increased travel actually lost a few fps, and I was wondering if the outside rim of the hammer was hitting the valve, limiting the lift in that situation.... I selected three different RVA settings, and ran the hammer travel through it's range to find out, with the following results....



4 turns out on the RVA is the most preload I can use that will not cause the spring to go coil bound with the maximum hammer travel (5 turns).... You will note that there is a small but definite LOSS in velocity with increased travel.... At 9 turns out, the velocity increases as you increase travel, reaching a peak at 4 turns, and then drops.... At 12 turns out (minimum preload), the velocity increases steeply as the travel increases.... That is as per the expected behaviour, as not only does this style travel adjuster increase the travel, but as the preload is constant, it also increases the cocked spring force, so with light preloads, you're getting twice the bang for the buck, and power increases steeply....

For both the 4 turn and 9 turn out RVA settings, there is a downturn in velocity at 4 turns out.... My assumption is that is the point where the outer rim of the hammer is hitting the back of the valve, limiting valve lift.... It would appear, therefore, that is the maximum travel the gun can make use of without further modifying the back of the valve to allow the momentum of the hammer to carry it further.... Is this worth doing?.... Considering I will never run the gun at those high power levels, probably not.... The efficiency would be terrible at the long dwells associated with that much lift.... At 2000 psi, I would likely not run this gun at over 950 fps even if it was tethered.... That means at least 9 turns out on the RVA at minimum hammer travel, even less if the travel is increased.... A good solution, at least for further testing, would seem to be to set the travel at 4 turns, giving a hammer travel of about 0.77".... This will result in very low preload on the hammer spring.... I may well need to try a shorter and/or weaker spring as I'm running out of room to decrease the preload to allow tuning the gun.... This problem will increase at lower pressures....

I'm going to have to ponder these results for a while to decide where to go from here.... I'll probably do some testing at 1600 psi to accumulate more information before making any changes....

Bob

[rsterne]

I did some experimenting at 1550 psi (couldn't be bothered resetting the reg to 1600).... I had to swap out the QB hammer spring for a weaker one as I couldn't dial it to a light enough hit.... The new spring is 2.0" long made from 0.045" wire.... I tried three different stroke lengths, with the following results....



What is interesting is that at maximum stroke, the velocity DROPS as you increase the preload to maximum.... The only thing I can think of is that the hammer is hitting the valve with enough force (less air pressure, remember) to rebound off it, shortening the dwell and reducing the velocity.... At one turn out from maximum stroke, the velocity has it's normal "plateau" or nearly so, and since I am going to be detuning the spring preload the hammer should never come in contact with the valve.... so that is the setting I used for the remainer of the testing....

I filled the gun to 1600 psi and bled and disconnected the fill whip so that the gun was operating on only the 28.5 cc of air inside the valve for the next tests.... The maximum velocity for a single shot at that pressure was 922 fps (48.0 FPE) with the 25.4 gr. JSB Kings.... That compares to 836 fps (39.4 FPE) at 1500 psi with the previous Carbine pumper I built recently.... so I've picked up over 20% in FPE with the longer barrel, bigger valve, larger ports, and a 100 psi increase in pressure.... I didn't spend much time trying for a two-shot setup, but I did manage 2 shots within 5% averaging 44 FPE at an efficiency of 1.0 FPE/CI.... I did play around until I got a good 3-shot tune at 38 FPE (808/834/813 fps) with an efficiency of 1.21 FPE/ CI.... That compares to the 3-shot tune at 31 FPE with the Carbine at 1400 psi with an efficiency of 1.10 FPE/CI....

I then filled the gun to 1800 psi and repeated the above procedure.... I never tried for maximum velocity, but I got 2 shots at 45 FPE with an efficiency of 1.00 FPE/CI.... and a 3-shot tune of just over 40 FPE (835/868/840) with an efficiency of 1.13 FPE/CI.... Those three shots used exactly half of the air in the valve, the ending pressure was 900 psi.... The setting required was about 4 turns out from coil bound with the 2.00 " x 0.045" wire spring, and the travel was 1 turn less than maximum....

Considering these are just preliminary results, I'm very pleased.... I have no idea yet how many pumps (or how hard) it will be to get to 1800 psi.... but based on the extra leverage the effort should actually be less than to reach 1500 with the Carbine.... I've won't be doing any pumping until the stock is finished and installed, which is 4 more days of oiling and sanding....

Bob

[lloyd-ss]

Bob,
Nice work, and obviously an effort driven by personal satisfaction.  The best kind.
The leading edge of the hammer can impact the back end of the valve and I ran into that with my 80fpe disco a while back.  There are a couple of remedies that will work, but your choice. The extra stroke length usually adds a nice boost to the power levels.
Lloyd

[rsterne]

I measured the pump leverage on the extended Billet linkage compared to the stock linkage I used on the Carbine.... When you measure from the main pivot to the center of your hand, the new gun is 16.5" compared to 12.5" on the Carbine.... Since the pump stroke is the same (and the link pivot in the same place), that means this rifle should require the same effort at 2000 psi as the Carbine did at 1500.... The 3-shot tune I had on the Carbine started at 1400 psi, so I decided to tune this gun for a 3-shot string at 1800 psi.... Once I made that decision, and based on the previous testing, I went through a series of RVA settings at various hammer stroke lengths at 1800 psi to develop a baseline....



I observed the same strange behaviour as previously at maximum hammer travel, so I took some measurements.... It turns out that when the hammer is adjusted for maximum stroke length, it can only open the valve 0.10" before it hits the back of the valve body.... Under normal operating conditions, this is not an issue, but a combination of maximum hammer stroke plus maximum hammer spring preload causes this collision to reduce the dwell, and hence the velocity.... However, since I would never run this gun at over about 950 fps (wasteful of air) I can run the maximum hammer stroke without a problem.... Each turn less on hammer stroke requires about a half turn more preload on the spring.... This increases the cocking effort and the load on the sear, and is likely to increase the possibility of hammer bounce.... so I maxed out the hammer stroke (to minimize the preload) and started looking for suitable tunes....

I wanted three tunes, one with a single shot at high power without wasting too much air.... a second one where you had two shots of equal velocity.... and the main one I was interested in, a 3-shot tune where the three shots were within a 4% maximum ES.... Here are the results, using 25.4 gr. JSB Kings....



The graph shows the velocity of the following shots so you can see what is happening.... The single high power shot worked out to 951 fps (51 FPE) and used 500 psi of air (0.85 FPE/CI).... The 2-shot string was 898 fps (45+ FPE) and used 730 psi (1.04 FPE/CI).... The 3-shot string averaged 846 fps (40+ FPE) and used 900 psi (1.12 FPE/CI).... If you needed a 4th shot, it would be about 725 fps (30 FPE), plenty good enough for a close follow-up or Coup de Gras....

How does this compare with the Carbine I built previously?.... That gun maxed out at 837 fps (40 FPE) for a single shot, delivered two at 796 fps (36 FPE) , or three shots at 739 fps (31 FPE).... so I've picked up about 100 fps and 10 FPE across the board.... To say I'm pleased would be an understatement.... Another couple of days of oiling and sanding the stock and I'll be able to try pumping this beast....

Bob