They did change the twist rate to a 1:7 but that really has nothing to do with the pressures the rifle can handle, it deals more with bullet stabilization. Prime example is when Century first released there Tantal it had 3 barrels, a 1:7 a 1:9 and I forget the third barrel. Since 95% of 5.45x39 on the market is 60 grain ammo it prefers a certain twist rate to stabilize the round. The 1:9 and the other barrel caused rounds to destabilize and keyhole. The 1:7 twist stabilized the 60 grain rounds perfectly and ended the keyhole issues. The US military had to change twist rates when NATO put there stamp of approval on a certain grain bullet in the 5.56 round for bullet stability. Now one little known fact tho, is if your rifle has a chrome lined barrel, you could still have accuracy and stabilization issues because any imperfections in the bore won't be worn down as the rounds go over them as they would in a non lined barrel.
