"It is unsafe to fire these rifles with the 155 grain Radway Green cartridge or any other commercial cartridge using the 155 grain or heavier bullet which has a diameter of .3083" or larger"

I take it that the NRA "Safety Warning" was not a blanket denunciation of the No 4/5 .308 conversion but rather a warning against re-loading with unsuitable charges and/or bullet weights.

This would certainly apply to any other type of hand gun.