300 BLK Home Bree issues

#1
300 BLK Home Brew Issues

I built this 300 BLK with the following components:
-10.5” faxon barrrel & pistol length gas tube
-PSA lower parts kit (includes standard spring/buffer)
-PSA nickle boron BCG https://palmettostatearmory.com/psa-ar15-bcg-5-56-nickel-boron.html

Shooting 147 grain reman FMJ out of G2 PMAGs.

Lube is light coating of CLP.

I have about 300 rounds through it. Every 100 or 150 rounds I get a Double feed at the beginning of a full mag.

Mag related issue? Looks like the edge of the bullet touches the tab on the inside of the PMAG.
 
#3
I would work down the rabbit hole of magazine related. 1- Is it the same magazine everytime? 2. Are these 5.56 magazines?

I know I have had similar issues- specifically with 220 OTMs in 5.56 PMAGs. Bought a few of the 300 BLK magazines and solved the issue.

Quick fix is dont load the 5.56 mags to capacity with 300 BLK. Should alleviate some of the pressure caused by internal geometry of the magazine with the 300 BLK.
 
#4
I would work down the rabbit hole of magazine related. 1- Is it the same magazine everytime? 2. Are these 5.56 magazines?
Thanks for the reply. To answer your questions:

1. Don’t know if it is the same mags every time as I’ve been using about 4 different mags each time I shoot it.

2. Yes, they are normal 556 pmags.
 

Nate Osborne

NateMac
Staff member
Moderator
#5
I will agree with the suggestion to try the blackout specific pmags. I have 2-3 of them, and they are especially useful for heavier bullets (147/150 gr+).
 
#7
Keep a paint pen or roll of tape in your bag. Anytime you experience an issue, regardless if you feel it was magazine related or not, mark the magazine that was in use during the malfunction.
Thanks for the tip. I do that on my old usgi mags but for some reason I haven’t done that on my pmags yet. First time I’ve had problems with the pmags and I guess I was just thinking it was something I screwed up on the build and not a mag issue.

Last weekend I numbered all my pmags with a paint pen to keep track.
 

Yondering

Regular Member
#8
Clarify what you mean by "double feed". If it's trying to actually feed two rounds at once, that could be a mag issue, but I've never seen that.

If it's actually a failure to extract/eject the empty while feeding a live round, that's not a magazine problem. Check your extractor and ejector carefully, check if the fired round has a damaged rim, and then figure out if your rifle is severely overgassed. Any of those things can cause that issue. A severely overgassed rifle can rip the rim off the case (failure to extract) and then attempt to feed another round.

Your ejection pattern can tell us a lot, but 300 Blk ejection patterns are a bit different than 5.56. If 12:00 is to your front and 3:00 is directly to your right, where does the empty brass land and how far away?
 
#9
It was not a failure to eject, but a double feed. Two live rounds trying to go into the same hole at the same time.

Shooting from seated on the ground, brass is landing about 3 or 4 feet away at about the 4 o'clock position.

I bought some Lancer 300 blackout mags and shot 100 rounds at a match today without issues. Might be fixed?
 
#10
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This is a Magpul 7.62x51 mag with Federal 149 Gr. XM80. Looks pretty similar. Looks like the round is touching on the left side tab inside the mag. Does not cause any feeding issues.
 
#11
It was not a failure to eject, but a double feed. Two live rounds trying to go into the same hole at the same time.

Shooting from seated on the ground, brass is landing about 3 or 4 feet away at about the 4 o'clock position.

I bought some Lancer 300 blackout mags and shot 100 rounds at a match today without issues. Might be fixed?
I have had MUCH better results with Lancer mags than with 5.56 PMags. On the order of never having a malfunction with them in about 500 rounds. The little convex area of the 5.56 PMags that keeps the tips of the cartridge pointing into the center of the magazine cause the 300 round to point inward because of it's larger diameter. I have not tried 300 PMags.
 
#12
I got the Lancer blackout mags and after a few range trips and a couple hundred rounds I've had no more issues.

Thanks for the advice guys.
 

shoobe01

Regular Member
#13
I use the 20 round Lancers for the .300 literally just because they seem not awful and are different (even feel) as another safety measure. They have worked 100% on my .300 (for the relatively little I have shot it so far) but good to hear I accidentally may have made the perfect choice :)
 

Yondering

Regular Member
#14
The 300 Blk Pmags are good to go as well.

If using the 5.56 Pmags, you really have to pay attention to bullet profile relative to the magazine rib that normally rides on a 5.56 case neck. That rides against the bullet in 300 Blk, and if using a bullet that is fatter in that location (usually anything 150gr+) it will cause issues.