New 300 Whisper

[Jerryr98]

I have had my Remington 700 based 300/221 for about a week until I screwed it up. I loaded 50 rounds, I weigh each charge, inspect my cases (powder level in the case) after all are charged and again as I go to seat the bullet. So after following Sierra's reloading data and firing 40 or so rounds, why did I blow a primer and send powder residue and muzzle blast/noise back in my face? I even pulled the bullets on the remaining loads and each measured exactly 10.7grs which is a low end starting load with Sierra's 200gr MK straight from the Sierra maunual. So now my new rifle has a screwed up extractor and my gunsmith wants to examine the rifle for any defects (other than the extractor, that's an obvious issue). But here's the kicker, since building mine he has built two AR based 300/221's. One functions fine with his H110 loads and the other has done the same thing to him that my bolt gun did? Even baffled him??? So I begin researching 300/221 loading issues. After reading of some issues on quarterbore from fellow whisper shooters I have formed an opinion that H110 should be avoided. Take a look at the one post titled KABOOM! While my mishap was not to that extreme I still find myself being gun-shy and lost as well. What the hell is going on? Sure seems to be a link with the H110 and the whisper cartridge and it doesn't look good????