Square Mark on Case Mouth

[BulletFactory]

Hi, I am having failure to feed issues with this 300 Blackout. I'm using a CMT upper, a BCM BCG, and a BCM 9" barrel.

I am getting these deep square marks on the case mouth, and I'm guessing this is part of the issue. Not sure what to do, so I'm back with some pictures.

Here we go.

http://i1313.photobucket.com/albums/t557/The_Prodigal_Sun/Neck%20Marks%20001_zps6r2nd7bg.jpg (http://s1313.photobucket.com/user/The_Prodigal_Sun/media/Neck%20Marks%20001_zps6r2nd7bg.jpg.html)

http://i1313.photobucket.com/albums/t557/The_Prodigal_Sun/Neck%20Marks%20002_zpswkgo733o.jpg (http://s1313.photobucket.com/user/The_Prodigal_Sun/media/Neck%20Marks%20002_zpswkgo733o.jpg.html)

[mcdaniel.mac]

Looks like it's hitting the feed ramps. What magazines and lower are you using? It's possible the mags aren't getting high enough. Another possibility is that the feed ramps are mismatched, but that's less common. Another possibility is that you're overgassed, and the bolt is mashing the round in before it clears the magazine. Gas problems are easy enough to fix if you know what bolt, buffer, and has system (length and port size) you're working with. The easiest fix is just to throw a heavier buffer like an H2 in and see if that fixes it.

Hope this helps!

[BulletFactory]

Aero precision lower
H2 Buffer
Standard Spring
Lancer 20rd mags
Pistol length gas system.


These examples were taken by locking the bolt back, then releasing it from the bolt release to strip a round off the mag, and chamber it.

[243winxb]

Neck diameter not larger then .344"

Nows the trim length? 1.368" or less.

[243winxb]

Ramps

[fatelvis]

Talk about a picture being worth a thousand words! Thanks for making it totally clear to me....