The rifle is a microgroove 336. I saw this happen the last range session when trying to shoot in a scope. After a very thorough cleaning of the bore and chamber and addressing the scope issues I got it back to the range, bore sited itand found the Federal Powershock 200 gr rounds were still keyholing. I switched to some Remington 150 gr pointed soft pointrounds and the keyholing imediately stopped. Nor did the 200 gr Rem round nose factory rounds. I'm wondering if this is just a case of the gun wanting what it wants or if there's something more going on. I'll clean it up good and see how it goes with the RD 190 gr I have loaded.