I have built several AR's but never dealt with a heavy barrel. My son and I are trying to change the original rail. First thing I noticed is that those barrels WILL NOT do well with a standard barrel nut. The barrel is that heavy. Secondly this rifle came with a compensator that has no flat wrench surface and it covers the crush washer. So I tried a thick flat head screw driver through the gas ports of the muzzle break with the barrel attached to receiver block on a vise; it would not budge to the point where I was afraid of putting to much stress on the receiver. Will heating the barrel help any? The diameter of the existing barrel nut is 39mm which about 4mm larger that the standard AR barrel nut. Any ideas welcomed, thanks.