Before my daughter was born I stumbled into a deal I couldn't refuse and bought a Remington Model Seven .243 Win as her future first deer rifle. A couple years later with another kid on the horizon I decided that in the name of fairness he deserved a rifle as well. After much debate and deliberation, instead of buying new I had one of grandpa's guns, a Remington Model Seven .223 Rem, rebarrelled to a 18" threaded 1/7 twist Shaw .223AI with the hope of shooting heavy 75+ grain bullets for short range deer hunting. I did their barrel break in process a few weeks ago and headed to the reloading bench.
Spoiler alert....a new rifle is wearing the crown as the most accurate in the safe.
IMR 8208 XBR got the nod as the first powder and Sierra 77 gr. TMKs as the bullet. The gunsmith that did the barrel install, chamber, and magazine set it up with 2.400 OAL rounds in mind so I loaded a few of those up but didn't reliably feed. I seated them deeper to 2.365 OAL and that solved the issues.
A new scope, some zeroing rounds in the center, then 7 loads 3-rounds each. All ended sub-MOA with velocities from around 2450 to a bit over 2700.
My best was the second fastest/hottest I loaded, a bit over the Sierra book max. Can be seen there in the top center and below. The hottest load had slight primer flattening and worse cratering than the rest. They all had some degree of minor primer cratering, even the bottom end loads, assume thats a firing pin thing. No other pressure signs.
I loaded a few more of those the next day and got similar results.
