WHY HAS NOBODY MENTIONED LUBRICATION?!?!?!
DID YOU LUBRICATE THE PISTOL PROPERLY??????
8/10 times I encounter the two following problems on GBB pistol repair;
1) The hopup was turned off
2) The pistol wasn't lubricated at all
I've seen MANY a GBB misfire, shoot poorly, get only 3-4 shots out of a full mag, just because the slide had improper lubrication and was either binding up, or the grease had stiffened up.
Take the slide off, clean all the sliding mechanisms VERY thoroughly, and regrease everything with high speed bearing grease, spindle grease or a light synthetic grease. Alternatively you can use a heavy weight silicone oil, but I find it just makes a mess.
Now this is where my MEU had all it's major gas efficiency issues;
Make sure the air nozzle moves back and forth freely. If it doesn't, the gun won't shoot right.
I'm unsure as to how the KJ system works exactly, but the TM version uses a fixed O-ring piston instead of the genius cup type piston on the P226. So anytime that O-ring gets a little dry it shrink and you lose most of your airseal, and thus most of your gas efficiency. Best to use a good thick gear oil or synthetic grease. Don't use lithium grease as it will eat the rubber.
Oh and if you shooting in temperature below 14 degrees, I wouldn't expect more than 8 rounds. Because the MEU has a very thin magazine, it holds only half the gas or other pistols. It's really a summer pistol...