Crosman 2260 PCP Carbine

[threex4]

With all the talk of making a PCP out of a 22xx gun, I recientely put mine together. After installing the Disco valve and fill port, pinning the valve and filling it with air and checking for leaks, I got to put it all together today and fired some shots thru it. I had to sight in my scope, again, but once it was sighted in, I shot a 5 shot string at 10 yards and I could cover the holes with a dime.



Testing of my 2260 PCP with a 16" barrel . Stock Benji valve and fill port. I used Disco spring , bolt and a HDD. The adjuster was installed but was not used.
Fill pressure was 1800psi. No gauge so I shot till the poi and fps starting to change. Total of 30 shots with starting at 779 fps and ending at 376 fps.
Time of test was 1pm and temp was 48* with winds blowing 5-10 mph from the NE. Target set at 10 yards .

Results : shooting with 15.9 JSB
1. 779.5,, 6. 773.4,, 11. 762.4,, 16. 707.9,, 21. 641.6,, 26. 553.9
2. 777.8,, 7. 788.3,, 12. 753.7,, 17. 695.3,, 22. 624.0,, 27. E2
3. 777.9,, 8. 776.8,, 13. 743.0,, 18. 683.5,, 23. 599.0,, 28. E2
4. 777.9,, 9. 774.0,, 14. 731.5,, 19. 669.3,, 24. 578.1,, 29. 419.7
5. 780.6,,10. 769.2,, 15. 721.2,, 20. 655.3,, 25. 553.9,, 30. 376.5

The first few shots I checked for leaks around the transfer port, bolt but found none. I did notice that it seemed like air was coming out of the front of the breech around the barrel.

I tried soaping but that didnt work, so I took a wet tissue which would stick to the metal
(wind was blowing which the tissue would not lay flat) , it defentely lets air out when shot, it kept blowing holes in the tissue.
When the pressure (fps ) seem to drop the air escaping around the barrel/breech seem to stop.

Any Ideas what may have caused this? Im using the ice tube and not the metal oem transfer port.

I will need to recheck with the metal transfer port and un-moded barrel.

[AK-one-shot]

Nice build and report. Thank you for posting that.

Gordon

[jake]

nice looking gun, and groups!

[ribbonstone]

Nice little carbine, looks like it would make a nice squirrel gun.

If it only leaks at the shot, then it's the transfer port not fitting quite right.  IF the transfer port is a little short, will leak at the barrel/breech joint rather than between the barrel and gas tube. If I'm right, you might find a slight leak as the front of the breech where the barrel enters as well (baby powder is good for that test). Idealy a transfer port will seal against the barrel and the valve, just passing through the air tube and the breech along the way.

Shot count seems about right for a gas tube that size running at that pressure...about 12-15 good shots, then a good bit of fall off with every shot.  That good power for running at that pressure.  Becasue the fast shots start right away, you might back off the hammer tension just a touch and gain a couple more +700fps shots.

[threex4]

Thanks Robert.  Yea I kinda figured the T port tube may have been the problem. I shot this gun for awhile on C02 and used the same poly tube rather than cutting a new one. Guess the 02 lower pressure didnt blow outbecause of any inperfection between the barrel and tube to mater.
I'm currently using a Disco hammer spring, with no tension from the power adjuster. in fact I think the spring may be too strong as its harder to cock this gun vs. my Disco, I dont know why, maybe the pin for the adjuster screw is causing a little tension on the spring.
 I have another stock for it a, DIY , just need to start working on it, but time is short this time of year, hopefully I'll have it done after the first of the new year. So  I'm just gonna shoot/play with it for awhile, just because LOL.  Plus every time I take it apart I have to resight in my scope, that sometimes is a PITA .
OH , this is my other urban squirrel gun.

[gamo2hammerli]

Nice groups with your carbine.  And sweet looking carbine in the 2nd photo.

[ribbonstone]

the easiest way to get a little longer "sweet spot" would be to decrease the pre-load on the sping (back out the adjusting screw or use a slightly weaker spring). Will get lots of dire warnings about how you'll bring about the end of the world, but if your comfortable inceasing the fill pressure to 2100, might be able to smooth out the shot curve.  

Idea would be to have the first two or three shots show a vel. climb (and ideally they wouldn't be more than 25FPS under the highest speed shots), kind of level off, and show a vel. decrease.  Your shot count showes it pretty much starts off at near top speed.  So to get a little "up swing", would need to:
1. Increase the fill pressure.
2. Decrease the hammer spring tension.
3. Decrease the hammer weight.
4. Decrease the hammer's stroke (which does almost the same thing as #2).

Without a lathe and the ability to anneal and reharden steel, count #4 out.  Can count #3 out unless you really want to grind two flats on the hammer (or lathe a belt around one section).  Can count #1 out if you are uncomfortable going past 2K.  Which pretty much leaves #2.

If I were doing this (and I just might give it a try on a 2260), would probably go for #3.  Have made lighter hammers for  Co2 and HPA run guns, and it does make for less velocity, but it also makes for a short fast bleast of air (shorter dwell time) which makes for a quieter gun and a much longer shot count.

Will post a few pictures:


Standard Crosman hammer:


Lighter hammer isn’t NOT FOR SPEED, ti will shoot SLOWER…but it does seem to make for a quieter gun, and the shot count goes up disproportional to the vel. loss.
Lightened by a lathe cut:


Lightened by  filing flats (need to break the hard outer skin with a Dremel, but the inside is soft enough to file):



Realive that the above does SLOW the gun down a bit, but the short-fast “blip” of air the light hammer seems to releases is quieter (less muzzle pressure) and seems to lose LESS speed in a short barrel than in a long one (which makes sense as the long barrel could make use of the longer dwell time of a heavy hammer).


My Urban Squirrel Carbine (USC):



The 2260 that might get the PCP treatment:

[ribbonstone]

Standard Crosman hammer:

Lighter hammer isn’t NOT FOR SPEED, ti will shoot SLOWER…but it does seem to make for a quieter gun, and the shot count goes up disproportional to the vel. loss.
Lightened by a lathe cut:
]

Lightened by filing flats (need to break the hard outer skin with a Dremel, but the inside is soft enough to file):


Realive that the above does SLOW the gun down a bit, but the short-fast “blip” of air the light hammer seems to releases is quieter (less muzzle pressure) and seems to lose LESS speed in a short barrel than in a long one (which makes sense as the long barrel could make use of the longer dwell time of a heavy hammer).


My Urban Squirrel Carbine (USC):


The 2260 that might get the PCP treatment:

[threex4]

Robert, I got some time today , dissambles and replaced the Tport tube with a longer one, used the 2260 spring and put it all back together. Its been raining all morning so I cant chrony it, no indoor area to shoot, I have to rely on the great outdoors . But I was able to shoot it some from out the back door. I topped the gun off with 2000psi shot a few pellets and no air from the barrel/breech area. one problem fixed, yea. the 2260 spring is way lighter than the Disco and  when I fired it , the gun was allot quieter than with the Disco spring, it just didnt seem to shoot as hard, even with the adjuster screwed all the way in. Now to wait for clear weather and I can chrony to see if the lighter spring gives the fps I'm looking for, otherwise it may get the heavier spring back in.  The TKO  on it works just fine.