5.56mm NATO versus .223 Remington Chamber Differences - Page 1 - AR15.COM From this link above...if my math is correct, the freebore (distance bullet travels before engaging lands) difference between .223 and 5.56mm is 0.152" (0.040 + 0.045 versus 0.073 + 0.164) Is my math correct? When I look for other information online I get most people stating a MUCH smaller difference in freebore between these two chamberings. I have a bushmaster in 223/5.56 chambering and am finding a huge bullet jump when I load my COL to 2.25". My bullet jump is around 0.174" and that seems HUGE to me...so I'm trying to figure out if that is normal or not. This rifle has never shot very well with factory ammo and I'm trying to work up some loads that might improve accuracy. This is the first possible "strange" thing I've come across that might be a clue to my poor accuracy. I know that this question is not a "long range" question per se, but I'm trying to turn my AR into a decent varmint rifle...so I'm hoping one of you experts out there might be able to help. Thanks for any insight on this.