Avenger .25 over 76 FPE!

[revenger]

Some of you may have read my intro thread and my other thread asking about how to get more power but I would like to create a new thread with my results. Stock out of the box my .25 avenger maxed out at 55 FPE. I added a 16 cc plenum and drilled out the barrel port and transfer port to 7/32". This netted me almost 60 FPE. Today I drilled out the port for the poppet to 15/64", installed a lighter poppet spring, and oval out the barrel port some more. On max power settings I reached 76.5 FPE on multiple shots with a 40 grain slug! Those last 2 mods may be worth more than any for sure. For reference this is the spring I installed from my local hardware store.

***EDIT** this spring is not appropriate for this power level. Possibly a good spring for undrilled ports but the fun required the extremely stiff stock spring to hold tight FPS deviation and grouping.

 

[Smitty911]

How is the accuracy? I understand that with thermal nuclear devices you don't have to be as accurate but it sure helps.

Smitty

 

[PumaCarl]

Nice work! I'm going to show your numbers to my brother and see if he wants to push his. He did the transfer port to 3/16" and had his otherwise stock gun up to 62fpe but that wasn't enough to get good accuracy out of the heavy NSA's we were trying, this might do it. Thanks

 

[revenger]

How is the accuracy? I understand that with thermal nuclear devices you don't have to be as accurate but it sure helps.

Smitty

Honestly all I did was assemble the gun
back together, throw the chronograph on and start shooting downrange to see if there were any improvements. I didn't even put on the picatanny rail to even re-mount the scope. I have a few different slugs now and have ordered several more to try. I want to be able to push a slug as fast and as accurate as I can for hunting at 25-50 yards. I can now shoot 33.95 jsb pellets at 1000 fps which is too fast. I will back that down to under 900 if I want to have fun.

Nice work! I'm going to show your numbers to my brother and see if he wants to push his. He did the transfer port to 3/16" and had his otherwise stock gun up to 62fpe but that wasn't enough to get good accuracy out of the heavy NSA's we were trying, this might do it. Thanks

No problem. The barrel port is perfect at 7/32 as it barely misses the o ring but you can oblong it out as much as you want. The poppet port really needs done on a drill press in my opinion. I did it with with a vice and my hand drill but I did have some sealing issues to start with until I went back in a couple times to file down a tiny burr that I accidentally created. Once I got 2k psi in the tank it didn't leak anymore. May just need adequate pressure to seat it. The transfer port itself I'm betting could gain some more increases. A tiny grinding bit that can reach down from the top may help gain a little bit more. FYI I did re-tap the top threads of the transfer port to 1/4-20 so I could put back a set screw in there to hold the barrel.

 

[revenger]

Update guys.. that spring is not strong enough at this power level. I was trying to dial the gun back down some and kept getting huge swings in speed which is obviously not good for grouping. So I switched back in the stock spring and I'm back to driving tacks. I'm sure that spring would be nice addition to a non modified gun but now I have so much more flow I believe I was bouncing the poppet. Good news is I am at 860+ fps/56 FPE with jsb 33.95's at 1600 psi where I could never reach that before in stock form. Seems keeping the pellet below 880 is the ticket for this gun.