There were more questions raised than answered in my post yesterday on the 300 AAC Blackout kaboom in a 223 Wylde-chambered AR-15, so I thought I’d do some more research.
I started last night by grabbing a 223 Wylde-chambered AR-15, which was easy for me since that is the chambering of my personal AR-15. For those of you not familiar with the Wylde, it is a modified chamber designed with the intent of handling .223 Remington and 5.56 NATO cartridges with equal success. Like the Noveske Match Mod 0 chamber, it is designed to work with longer and heavier bullets .223/5.56 bullets in the 77-80-grain range favored by longer distance shooters.
My second task was locating Remington-branded factory 300 AAC Blackout ammunition. I was able to find a box each of both 115-grain closed-tip flat base (CTFB) and 125-grain Match King Flat Base (MKFB) cartridges.
I loaded one of the 115-grain Remington CTFB 300 AAC Blackout cartridges into a standard-capacity 30-round GI aluminum magazine, inserted the magazine into the mag well, and allowed the bolt to run forward. The bolt did not close, and while I didn’t have a caliper handy to measure the exact distance, it seems to have stopped short about 1/4″ from chambering. I ejected the round, and noticed the feed ramp had scraped the jacket of the 30-caliber bullet. I then replicated the same process with the 125-grain MKFB cartridge. It also failed to fully chamber, and left a scrape on the .30-caliber bullet from the .223 feed ramp.
At no point did I attempt to fire either cartridge, because, “duh.”