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Alan Alford's build

2250b Tube for later move to bulk CO2.
12" .22 Caliber Barrel from Doomsday Backpacker
Brian & Assoc. Alluminum Breech with 2 barrel screws
Original site rear
Pin site on Custom Mt. Airguns Muzzle Break
2x1 Centerpoint Scope with UTG dovetail adapters
Mountain Airguns Custom Bolt and Handle
Mountain Airguns Custom Power Adapter and spring guide
B&A Boss Valve for extra Power

Built mainly for fun and to shoot at local Field Trial Pistol Match.

It currently it shoots a 14.3 Crosman Hunting Pellet at about 530 fps in a 72 degree room for 8.92 FPE.

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Chrono Results for 2240 Valve Extension and 1377 Valve Stem Exhuast Valve

June 21 2012 at 8:58 PM
zach allen  (Login sonargodz)
Crosman Forum Member
from IP address

Here is my latest chrono results. The first string is a stock valve with a slightly ground down stock poppet head and the piercing pin removed, stock hammer spring, and stock valve spring. No other mods done to this valve at this point other than the Protop and the Valve Extension installed.

The breech is Cothran Machine with hollow bolt. Gun has a 12 inch barrel. Velocity Adjuster was unscrewed all the way, so no extra tension on the spring. Also used one of Anthony's Protops to test the gun with 12 gram cartridges.

Here is my original string when I started modifying this valve with 12 grams.......

Temp 68 degrees using co2 12 gram
14.66 grain Beeman FTS domed
CED Millennium Chronograph


Then I rebuilt the valve a little. It was modified with a 1377 valve stem installed and the main exhaust port reamed out to .243. It now has a 1377 valve stem, stock weight valve spring, and stock weight hammer spring. Exhaust valve is drilled out a little but there is no other mods, porting or polishing.

Temp 60 (too cold!!!) degrees using co2 12 gram
14.66 grain Beeman FTS domed
CED Millennium Chronograph


I got tired of waiting for the weather to warm up, so I installed my 2240 Powermax HiPac on the gun (being as the valve extension is 1 5/8 longer, the difference between a 2240 and 2250 tube), and these are the numbers that I got off of 1250 PSI:

No tension on Vel Adjuster Half Tension Full Tension
630 649 646
654 635 615
642 607 586
629 582 550
617 560 500
596 517 449
574 477 398
553 423 empty
532 386 empty
485 331 empty

I also filled it to 1300 and got my first shot at 660. Mind you this is a stock hammer, hammer spring, and valve spring. I had a half a turn on the velocity adjuster for that shot.

This message has been edited by sonargodz from IP address on Jun 22, 2012 1:01 PM

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