Wednesday, June 23, 2010

Here's how my 1377 "Ultra Carbine" performs

Ok guys, I finally got you some numbers with the A.C. Custom parts flat top piston and valve installed. I have a 10 shot string I shot over my chrony and a few shots at higher pump levels as well to see the power increase. I am pretty happy with it considering it's using a stock 10.1" barrel and stock transfer port.

First for a little info on what the gun has installed that would possibly affect the power, then the numbers. It has a Crosman steel breech and a Mac1 brass bolt with extended probe and 90 durometer urethane o-ring. It has a blued steel Stace barrel band with a solid dowel pivot pin and c clips. I'm using a stock transfer port and of course an A.C. Custom Parts aluminum flat top piston and power modded flat top valve with his power hammer spring and guide. The barrel is a bone stock 10.1" Crosman 1377c .177cal barrel. Nothing would really affect the power at all over stock except maybe the extended probe(maybe 5-10fps) and definitely the piston/valve. Before adding A.C.'s parts I was getting 510 FPS on 10 pumps using 7.9gr CPLs. After installing his parts I am now getting an average of 627 FPS on 10 pumps using the same 7.9gr pellets. That's an increase of 117 FPS!! Then I pumped it up 15 times and took a shot, 705 FPS!! Then I tried 20 pumps, 760 FPS!!! Then I tried 25 pumps, 790FPS!!!!! All with a 10.1" barrel, stock transfer port using 7.9gr CPLs. To me, that is nothing short of AMAZING. Anyone looking for a power increase should start with the flat top piston/valve set up first and foremost. Absolutely incredible.

I stopped at 25 pumps, because the valve was starting to retain some air and I knew I was reaching the limit of what that set up could do. I am totally impressed with it now. This one's a keeper! Here are some numbers for you.

Here is a 10 shot string using 7.9gr CPLs and pumping 10 times per shot. The consistency is amazing as well with only a 7 FPS extreme spread! That's good enough for Pistol FT use right there!

Hi 630 FPS
Lo 623 FPS
Avg. 627 FPS
ES 7.24 FPS
SD 2.64 FPS


Hope you enjoy your 1377 as much as I do!


  1. Joe,

    It's a Leapers Red/Green dot sight 1x no magnification. Works great.