I have a Spikes AR that I picked up second hand. The lower is marked multi-cal, and SBR, model ST15. It has a 16" barrel stamped 5.45X39 1/9. The bullets tumble right out of the gate.. at 10 yards the bullets literally hit the paper sideways, and tear a bullet shaped hole in the target. I've tried several kinds of ammo and different flash suppressors. I have several thousand rounds of the 5.45X39, and really like the caliber, but I'm ready to just rip the barrel out and and put a 5.56 barrel on it. Any ideas? I'm an avid shooter and reloader, but don't claim to be a gunsmith. Anybody got any suggestions?