Upgraded my FX Impact MK I to an external plenum. Now shooting .30 caliber pellets (44.75 grain JSB) at 856 fps, (50.15 JSB at 832 fps). 92 bar, 63+ shots per fill with 480cc bottle. Did not use power plenum. Maybe later. For those that don't know, the external plenum is the big silver thing hanging down below. It's an extra capacity air tank that increases the available flow per shot.
Before the external plenum, I was running just under 150 bar to get similar fps, and only about 30 shots per fill. I am loving the 63+ shots per fill now at the same power levels. That's 2 and a half magazines (24 round magazines), Could maybe even squeeze 3 mags with maybe a little loss on the last few shots, I haven't pushed it that far yet.
Kudo's to Vladan Paunovic at Fx Impact power upgrades for this wonderful 75 cc Beast titanium external plenum and kit. The kit inlcuded other internal parts required as well. His site shows different tunes capable of over 1,000 fps at 100bar. I prefer this lower tune for accuracy and shot count since shooting pellets, not slugs.
Accuracy is great. Check out the LabRadar chart. 2.7 fps standard deviation with only 10.7 fps extreme spread in 14 shots. Every bit as good as before the change. I'm not the most expert shooter, but holding a nice single hole under a quarter group at 50 yards. Check out the video. The top right target is 14 shots, the center 10 shots with one flyer.
Here's the scope cam video (25x magnification) video of the 14 shots (top right) at 50 yards. One inch squares. The center had 10 shots with one flyer.
Shipping took a while with all the Rona delays. Not for the faint of heart. This was my first time having any airgun apart. I thought I really messed up and broke the gun once, but replacing a torn o-ring and re-adjusting the regulator did the trick. (Read the manual! Do not adjust reg down without de-gassing properly!)
It took me probably over 200 pellets through the chrono to get it tuned again, mostly from my lack of experience. I kept trying to run the bar higher, when the gun is quite happiest at the 92 bar.
I know many folks send theirs off to get done, but I kind of like to tinker, that's half the fun of these, is their tune-ability! I am very happy with this kit and build.
Thank you Vlad!