Quote Originally Posted by jsbhike View Post
I think it is more of an issue with handguns than bottle neck rifle cartridges. It is sort of creating additional free bore.
I think the issue is really case capacity, burn rate, and intended peak pressure. Setback is very dangerous when the case is small, already full, and on the edge of pressure issues - 40 S&W, 357 SIG, 5.7x28 FN. Much less of an issue for larger cases, often from older cartridges like .30-06, .357 Mag, etc. The issue is whether a dangerous pressure will develop in the confined space before the bullet starts moving. Supposedly 5.7x28 is crazy dangerous for this, to the extent that reloading is not recommended and has extra warnings in load manuals.