Alright, so I have my friend's Echo1 SCAR right now and I took it apart to clean, re-shim, and to install new parts. But, when I got it back together it won't shoot with the 8.4v battery he has with it, but then I put my 9.6 in it and it shoots perfectly fine... Then, I put a different sized 8.4v in it and it shoot just fine, then I put his battery in and it won't shoot again. But, when I put my battery that's the exact same one as his, it won't shoot. So to recap: 8.4v (his)-won't shoot. 8.4v (exact same as his, just mine)-won't shoot. 8.4v (stick)-shoots fine. 9.6v (mine)-shoots fine. I have no idea what's going on with this, he's coming by today to pick it up, so I need help soon.