I knew a VN era SEAL Stoner gunner who would clip the tips off of all of his ammo. Jungle ranges, he wanted them keyholing all over the place! Illegal? I guess. Did he care? No.
I was a puppy pusher for a while when I went in and we'd use valve grinding compound and an electric drill with a cleaning rod and bore brush....our rounds from an XM177 or GAU5A/A SMG would keyhole in such a fashion after we removed almost all the rifling . Albeit most of my grass cutting was Thailand at NKP it was done!