Just finished my 8.5" upper (save for sights and a handguard) and took it out to test it out. Only fired 20 rounds through it as of now but everything went well. 10 rounds of Gunn 130gr SOST and 10 rounds of 187gr Gemtec Subsonic Predator tip. The 130 gr functioned fine. Its a thumper for sure. BCG locked back on last round as it should. The 10 rounds of 187gr was almost comical. Not loud at all, soft shooting but it did not lock the bolt back as I figured it might not but oddly, the last shot I'm pretty sure was a slamfire as it doubled. Gotta decide on a muzzle break to help the subs out until I get my suppressor.



Aero upper, Mas Defense 8.5", 1/8 twist bbl, AAC FH (the bottom)

Anderson stripped upper, 10.5" 556 1/7 twist nitrided barrel (top)

Might trade off the 556 parts to finish the 300.