I started collecting parts for a NEW 223 SUPER VARMIT AK (I hope to do a photo shoot of the build and post in the future) and I bought a high dollar barrrel off the NET chamberd for 223. It was originaly set up for a compitition bolt gun and was guarranted to have been shooting sub .400" groups I got to cheaking it out and found that it has a very tight neck and will likely require neck turning of the brass.
the reson I am posting is that this is a safety issue that has not really been adressed here when using take off or unknow barrels.
A tight neck can cause the bullet not to release as it is pinched buy the chamber and this can cause very high pressure. also free bore should also be checked as it is posable on a custom barrel that the bullet can actually be hitting the rifling and cause higher pressures.
just a couple things to keep in mind for guys who find a great deal on a bench rest barrel or some unknown nonfactory barrel.