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rsterne · Moderator

I wasn't sure if I should continue the thread on my 22XX PCP project, but decided to start a new one because this gun is so different in concept.... After refining my "Uber-Carbine" pumper, and then spending a lot of time working on my Disco and the 22XX PCP (which ended up regulated).... I decided to see what I could come up in a PCP doing the minimum changes to a 2260.... Modifying a 2240 or a 2250 carries other problems related to PAL and non-PAL and the possibility of ending up with a restricted firearm.... so I decided to start with a 2260 since they are PAL to start with, and a rifle.... no legal problems in modifying them.... Cool

There has been a lot of interest lately in doing these PCP conversions, and safety is always a concern.... especially since the 22XX main tubes were never designed by Crosman to be pressurized.... When I looked up the specifications for mild steel tubing of the same dimensions, I found a safe working pressure of 2000 psi.... The QB series (based on a previous Crosman design) DO have factory accessories which allow you to bulk fill them.... and it is well documented that CO2 pressures can reach 1900 psi at 120*F, even when the reservoir is not overfilled.... The QB uses the same size tubing as the 22XXs do.... Many 22XX HPA conversions run 1400 psi, and it is common for such set-ups to have an 1800 psi burst disc.... It seems to be the concensus of those who mod these guns that pressures up to about 1800 psi are not unreasonable.... but one thing worries me.... the Roll Stamp.... Shocked

The main tube of the Disco has the information painted on, while the 22XXs use a process where the information imprinted on the side of the gun is done so by pressing the letters into the side of the main tube by a method called "roll stamping".... I have seen several examples of 13XX and 22XX tubes where the letters were so deeply stamped that you could see imperfections in the inside of the tube when you look at a bright light through it.... This just HAS to weaken the tube.... .... The roll stamp on the 2260 goes about 1.5" forward of the front of the valve, so I decided to only pressurize that portion of the tube forward of the roll stamp.... Since I would be using a Discovery valve, and I wished to have a guage installed similar to that in the Disco.... it didn't take rocket science to figure out that making a new front end for the Disco valve incorporating a guage mount and moving the O-rings forward of the roll stanp cured all the problems at one go.... yourdaddyjoe (Muzzle Mack Products) and I collaborated on the design, and here is my version.... Cool

I decided to start with a stock Disco valve, as the performance I am after (and the very limited air reservoir) won't require improvements.... Since the 2260 breech screw is further forward than the one on a Disco, I machined a small notch in the top of the valve behind the transfer port to clear the 4-48 screw.... (Optionally, you could use a Disco steel breech and a Disco hammer).... The 2260 tube was drilled with three 5/16" holes for the Disco valve mounting screws.... These are in the same location as the transfer port, and 90 degrees apart around the tube.... I measured the guage location in a Disco and decided to use the same location for the guage port in the 2260 tube so that a Disco stock would fit perfectly, should I ever want to do that.... That puts it 1.125" ahead of the front trigger mounting screw hole (C-T-C).... The hole is 7/16" diameter, which allows slight clearance for the guage extension.... Wink

Now it was time to make the valve extension.... I machined the rear threaded part to be identical to the Disco part so that I could use the original O-ring.... same threads, same spring seat.... so the valve is identical inside to the original Disco part.... The front portion is 2.625" long measured from the shoulder.... I machined in a 0.100" deep notch 1/4" wide to clear the front trigger screw.... The extension is drilled 1/4" right through, and the front end is drilled 15/32" for a depth of 1/2".... The O-ring grooves are the same dimensions as on the Disco valve, same distance from the front.... and the rear O-ring is about 1/8" ahead of the front of the roll stamp on the 2260 tube.... The hole for the guage extension is drilled and threaded 1/8" NPT so that the end of the adapter is flush with the edge of the 1/4" center hole when screwed in fully.... One word of caution here.... If you had to replace the rear portion of the valve, it is extremely unlikely that the notch for the trigger screw and the guage port would line up because of thread "clocking".... Rolling Eyes

I will be using a B&A Bulk Fill adapter equipped with a male Foster fitting to fill the tube.... Since I will be using a hand pump ONLY, I have not bothered to fit a 1.8K burst disc.... but if I was going to fill from a SCUBA tank, even a regulated one, I would add one between the trigger screw notch and the guage port for safety.... I measured the length of the reservoir, and it comes out to just under 9" for a volume of about 65 cc.... half that of a Disco.... I should therefore be able to expect about 10-15 shots at Disco velocities.... I also intend to experiment with various hammer springs (2200, 2289, 2240) and see what I can get at lower velocities and lower fill pressures.... This might just end up being a replacement for my "Uber-Carbine" grouse gun....

I enjoy bouncing ideas off of Joe, and he seems to value my input as well.... That's the great thing about forums such as this.... sharing ideas.... Cool

Bob

rsterne · Moderator

I've been working on developing my PCP Carbine over the last week or so.... I'm using a 14" barrel, 2260 tube with my extended Disco valve and Disco guage, B&A Bulk Fill, a 2260 hammer with various hammer springs, and my own Velocity Adjuster and Barrel Band.... I cut away the rear part of a 2289 foregrip to fit around the guage which secures the back.... and made a custom barrel band to mount it at the front with just one screw.... It has a Disco Muzzle Brake and a Crosman Steel Breech....

I tried a variety of hammer springs adjusted all the way from coil bind to basically as loose as I could set them with my adjuster.... The Disco spring I used was "Set" by compressing it to coil bind, which reduces the length about 1/8".... I also tried a 2240, 2289, and 2200 hammer springs.... The 2289 and 2200 springs are longer, and you can't run the adjuster in as far, so the travel ends up being limited.... Since they were between the 2240 and Disco springs they ended up being redundant anyway.... The first two graphs are using the stock 0.140" ID transfer port and JSB Express 14.3 gr pellets.... All shot strings started at 2000 psi but only shots within 95% of the maximum velocity are shown on the graphs....

The 2240 hammer spring gave adjustments from the high 500s to the mid 700s and produced strings from 15 to 19 shots in length.... The shot strings were very ragged, and what you can't see is the first part of the strings, (below the 95% cutoff) which was even worse.... some shots were nearly 50 fps variance between consecutive shots.... There was no point pumping over 1800 psi.... Shocked

The Disco hammer spring increased the velocities about 100 fps, and gave adjustments from the mid 600s to the mid 800s.... When cranked near maximum tension, however, it was really too much power with the 14.3 grain pellets, and the shot strings were only 5 shots long to 95%.... Although the beginning part of the strings was still a bit ragged, they were not as bad as the 2240 spring, and were beginning to be respectable.... They were 13 to 16 shots long.... Wink

At this point, I dropped in a "non-PAL 1377" transfer port which was only 0.109" ID.... The idea was to smooth out the shot strings and lengthen them at the expense of top speed.... It worked....

At the high settings, the loss was about 50 fps over the stock 0.140" TP.... In the midrange, the loss was about 30-40 fps, and at the lowest setting the loss was only 20 fps.... This makes sense, because a smaller transfer port is less important when you aren't trying to stuff a lot of air through it.... The shot curves are noticeably flatter, with much less shot-to-shot variation.... and they are longer, from 14 to 20 shots in length.... Cool

I then experimented with 18 gr. pellets, as the intention of this gun is a high powered multi-shot Grouse blaster.... I've always wanted to try Crow Magnum pellets on a Grouse, but my Uber-Carbine pumper is a bit wimpy for them.... not this gun.... Twisted Evil

.... As I am finding with most PCPs, they love the heavier pellets.... The shot strings smooth out, the FPE goes up, and so does the number of shots at a given energy level.... I won't bore you with all the details, but after experimenting with a bunch of combinations, I settled on a mid-size transfer port of 0.125" and near the middle of the adjustment range using a Disco spring....

The results speak for themselves.... The three curves on the graph only cover one turn of the velocity adjuster.... I wanted to be able to pump the gun to 2000 psi and yet get the longest, flattest shot string I could.... I was also aiming for 20FPE, which I attained.... Here is the summary of the results at 4.4 turns out on the adjuster:

.22 Caliber PCP Carbine, barrel length 14"
Pellet weight 18.0 gr (either JSB Heavy or H&N Crow Magnum, it loves them both)
Average velocity over 14 shots: 703 fps with a total spread of 34 fps (plus or minus 2.5%)
Average velocity over the middle 10 shots: 709 fps with a total spread of 22 fps (plus or minus 1.5%)
Average Energy: 20.1 FPE over 10 shots
Pressure range 2000 psi down to about 1200 psi at 14 shots.... about 45 pumps to refill.... Mr. Green

I'm very pleased with these results.... I have a scope coming and can't wait to start the accuracy tests.... Should have this gun ready for hunting season on Sept. 10.... Twisted Evil

Bob

Brutuz · Senior Member

As allways... I'm impressed by your creations and craftsmanship Cool

firemandivi · Member

That is truly impressive. What do you plan on hunting with it?

Jaxom · Senior Member

Bob,

Learned alot from your write ups and experiments. Between you and joe, I wouldn't be surpise if some of the imfromation you shared and all, that some of these improvements don't "suddenly" find their way into some of the crosman lines of of ag's. This is a very tight knit community, I wouldn't be surprised if they weren't reading these forums.

yourdaddyjoe · Supporting Member

The first small batch of Extended valves hit eBay tonight....

Bob did awesome write up for my website too...

Thank you soooo much Bob.

This is what it's all about... I love working with other guys to get these ideas and concepts out there for all to have access to. Safety is my #1 concern... I don't like to hear about carnage on a mod... Especialy if we put our heads together and run senarios till we get it right...

This is meant to be fun. I love it!

yourdaddyjoe · Supporting Member

How is the crown on that puppy?

With my HPA 2260 Disco Wanabe Carbine poppin' beer bottles at 220 yards... I am happy with this style of crowning... Sooo much that when I do a custom Cut & Crown job... this is what my customers get...

Same 2 step style used on the AirForce/Walther Loather match barrels. And you get a little lip to help protect the crown...

I was not supposed to tell ya that we shoot shotgun primers at 40 yards... oooops... Nice little reactive targets.... he he... Mounted in Lexan and pressed in very carefuly....

Guy made me do it!! Twisted Evil

rsterne · Moderator

I intend to try it out on Grouse with Crow Magnum pellets.... Mr. Green

Joe, I really enjoyed working on this project with you.... I agree that this is the fun of these forums, finding like-minded people so that you can bounce ideas back and forth and improve the sport one aspect at a time....

Glad you liked the article for your website.... hope it brings you lots of business....

So what's next?.... Wink

Bob

yourdaddyjoe · Supporting Member

What's next.... Hummmmm

I cheated and used a Die to make the threads on the valves... Got that down to an art using the chuck and tail stock to square the threads dead center...

Now I just need to become more proficiant at threading with the lathe (the right way) so I can make the fill caps... after about 10 trys... I gave up... Lazy me....

I want to produce two models of "Loaded Gas Tubes" for novice AG builders instead of piece together kits... Loaded from end to end with what we found to be the best combo of internals for Dual Fuel use...

Complete tubes that the end AG user can just install thier Uppers, trigger groups and wood work to...

One 2260 based on what we just worked on and another in 2250 for Rear Tank AGs...

The issue with the rear tank AG is once the pin is depressed, the darn HPA tanks lock on with the high pressure to the ASA threads... which defeats the purposs of being able to remove the tank at your will...

You can muscle a 850 psi Co2 tank off no prob... But 1600 - 2000 psi HPA... forget it... You'll strip the bonett off the regulator first...

If you don't get the pin valve depressed enough... you get flow problems... (Sinper... get your mind out the gutter)

I need to come up with an on/off/bleed valve that I can build into the ASA fitting. This damn bleed valve is the hold out...

The only thing I have been able to do is add a in-line ON/OFF valve to the tank... Which opens another issue... Tank length and it must be installed before filling the tank and remian on the tank...

The 18 ci tanks are okay with a in line on/off valve... but... it will be some time before P.S.I. has the deal with Catalina Cyl. for more 18 ci tanks to be made... leaving us with the smallest 13 ci tanks...

I tried a 22 ci on Purple Can Killer... and ya mine as well be holding a rocket launcher or some bagpipes... no bueno....

rsterne · Moderator

I have screwed and unscrewed an ASA fitting (with safety vent hole) running at 2000 psi, but there is a trick to it.... You have to lubricate the threads with Teflon grease (non-oil based trailer ball grease) before installation.... I work the fitting several times with no pressure to make sure there is a thin film of grease all over the threads on both halves.... then wipe off any excess on the pressure side of things....

These is certainly more resistance on the threads at the higher pressures.... and you can blow an O-ring pretty easy at 2000 psi when it uncovers the vent hole in the outer part of the ASA fitting.... but I haven't had any serious problems.... No question a bleed valve would be a much better and safer arrangement....

Bob

sniper · Silver Status Member

the gutter is where i get my inspiration. Laughing

another great thread bob!!! as always!! Thumb Up!

and joe, my name is not sinper. Rolling Eyes

yourdaddyjoe · Supporting Member

I'm sorry snipper... I had just woke up and had not had coffee yet... Faq-U

dummyracer36 · Senior Member

just one question Bob, when are you gonna start offering these works of art for sale??????????????????????

rsterne · Moderator

DR - About the only thing you can hope for is when I tire of one and move on to the next.... Rolling Eyes

.... You'll have to support guys like Joe who are trying to make a living at this stuff.... for me it's just a hobby.... Besides, nobody wants to pay for the time it takes.... Mr. Green

I installed a 4 x 32 AO Leapers scope in medium height rings.... raised the comb and shortened that lanky Crosman stock.... and installed a Crosman trigger shoe.... The complete gun comes in at just 4 lbs. 11 ozs. as shown.... only 29" long.... Cool

I also extended the bolt probe and picked up 10 fps.... Now to get this thing sighted in before hunting season next week.... Mr. Green

Bob

rsterne · Moderator

Finally got a chance to get outside and sight in the Carbine and check the ballistics coefficient and the remaining velocity and energy.... First of all, here is the final target after sighting in at 20 yards:

JSB Heavy 18.0 gr. pellets - 5 shots under a dime.... This was repeatable, and there was very little variation of POI between the first 5-shot group, the middle group, and the final 5 shots out of a 15 shot string.... Had I shot all 15 shots in one group, you could have easily covered them with a quarter.... Mr. Green

The Crow Magnum pellets shoot to the same point of aim, but typical 5-shot group size is twice as big.... I then ran 5 shot strings over a Chronograph at the muzzle and again at 25 yards with both pellets.... shooting right in the middle of the shot string from 1700 psi down to 1400.... Here are the results:

JSB Heavy 18.0 gr.
Muzzle velocity: 715 fps, 20.4 FPE
25 yard velocity: 664 fps, 17.6 FPE
Ballistics Coefficient: 0.041
C-T-C group at 20 yards: 0.5"

H&N Crow Magnum 18.0 gr.
Muzzle Velocity: 712 fps, 20.3 FPE
25 yard velocity: 583 fps, 13.6 FPE
Ballistics Coefficient: 0.015
C-T-C group at 20 yards: 1.0"

Considering that the two pellets start out with virtually identical energies, the Crow Magnum has 23% less remaining punch at 25 yards.... I think my choice is clear for this gun.... once again, JSB pellets come out on top.... Cool

Bob