need help with new 300 BLK build

[!Nvasi0n]

Shot my several firsts tonight. First 300 BLK, first build including upper, and first time shooting a pistol AR. I plan to utilize the pistol this year for dear season until my SBR Paperwork comes back...

First off here are the Specs:
DSA Stripped upper (This is going to change, i am going to change it to a VLTOR upper soon...just impatiently dropped the coin in an effort to get the gun together.
BCM BCG (Thanks Grant
AAC 9" 1:8 twist barrel (Thanks Rob)
Spikes ST2 pistol buffer tube kit...i think this is basically a H2 buffer with a polished/ground stainless spring.
Noveske KX3 Pig
Spikes 10" BAR rail
DPMS LPK
BCM Gunfighter Mod 3 CH (Thanks Grant)


I used 115 grain UMC for break-in ammo. (Only 60 Rrounds so far)

First thing i noticed was that it DID NOT BLOW UP....YAY!!!! I WAS SO NERVOUS.
Second thing i noticed was the ejection pattern, very consistent, 4:00 pattern about 4'-6' away.
Third thing i noticed was that the case mouth opening had a consistent dent in it. About a .0625"-.100'' flat spot on the outer edge.
Fourth thing i noticed was the brass color/remnants on the case deflector...like i had shot about 500 rounds. So i can only assume that the dent in the brass is coming from a few things. Correct me if I'm wrong please. KX3, extra back pressure. Pistol gas system, Extra back pressure. BCM BCG W/Crane O' Ring. For added extraction power. All these things added up for a violent extraction cycle.

The last thing I noticed. I run a Blue Force Gear Sling. And if i "Punch it out" and shoot sometimes it would fail to feed. Basically the case would nose dive slightly against the upper/magazine, and i could simply smack the magazine and hit the bolt release and i was good to go.

But on 2 or three occasions, this happened while shouldering the weapon too. I was running, only one PMag. In all i experienced 5 FTF's 3 while "punching out" and 2 while shouldering it.

Should i try:
Different ammo (Sub sonnic, or higher quality supersonic)
Different magazine's (USGI's and PMag's)
Different weight spring
Different Weight buffer
Or something else?

I'm not terribly worried about the dented case mouth opening...unless you all think i should be.

thanks in advance for the help...

[fixit69]

The brass I can't help you with, ran less than 20 rounds when I put my 300 together(BCM upper, cmt auto BCG, AAC 9" barrel same as yours). I have a lot of work to do, seemed like I had a 25ft plus ejection with 135 supers, 10-15ft 220 subs with AAC 7.62 can. Need to play with buffer and springs when I get back home

Let me tell you this. I have a spikes lower, ordered with the ST-T2, and that buffer has been nothing but a gigantic pain in the ass. I shitcanned mine, won't use it for even a backup.

Use regular buffers and see if that changes. Might help might not.

ETA: when I say regular buffers, I mean standard carbine, H, H2, H3. Maybe try the newfangled A5 systems with different buffer weights. It will be months before I can get back to play with mine, so good luck and let me know what you find out. It might help me in late November.

[!Nvasi0n]

Thanks for the advice!

I'll look into the A5, or H3 system