[Unclenick]

Ron hit the magic question. How long are the cases? A SAAMI case neck at maximum is 0.2027" long, and a SAAMI chamber has a neck minimum length of 0.2201" for .223 Remington, or 0.0174" extra room. Clymer's chamber dimensions eschew the fourth decimal place and show 0.220" for .223 Remington, and 0.218" for 5.56 NATO chambers. So their chambers have an extra 15.3 to 17.3 thousandths for neck room. Hard chambering can set shoulders back several thousandths, and, given its light weight, I would expect a limit of maybe 5 thousandths in the .223/5.56 cartridge. So there should be at least 0.010" extra to play with.

Note that the risk as already described is jamming of the case mouth into the throat of a chamber, preventing normal bullet release and thus raising pressure. So COL has nothing to do with it. I know some of the old timers never trimmed and seemed to get away with it. If you have a chamber with a sharp corner at the end of the neck this may work for the same reason the RCBS X-die can keep cases from growing beyond a point, and that is by the end of the chamber neck pushing the case neck back. I am leery of trusting this, especially not with a ball throat which is tapered rather than having a sharp shoulder at the end of the neck. I have not experimented with this not only because of the safety concern, but because I go to some trouble to try to keep case necks straight for accuracy. Such a push back on the neck in the absence of a coaxially restrained mandrel inside an X-die, seems likely to tip the neck on the case body.

I would be extra careful to have enough room for the neck in the AR and other self-loading rifles with military type floating firing pins, as jamming a neck against the end of the chamber, even if it just pushed the neck back, increases risk of a slamfire.