So I took out the 300BLK today for the first time. It shoots great and I love it so far. However, I ran into the below issues.

1) Shot great with Hornady American Gunner 125gr rounds. First round, it didn't lock back but then it did after that. Figured initial break in friction as the problem. Switched to Hornady 190 gr Sub-X subsonic rounds, and it cycled just fine. However, the bolt would not lock back after each last round. I'm using a standard carbine buffer and the bolt and gas block came with the upper from PSA. I'm wondering if I should get a lighter bolt. I'm assuming a standard gas block is already opened up fully, unless in mistaken. I intend to use the subsonic rounds for home defense.

2) After running 70 rounds though it, the chamber was filled with brass shavings.


Once home I inspected some of the empty brass and noticed they all had two nicks.



Thinking maybe from feed ramps, but not sure. Any idea on what contact points cause this issue? I was using the polymer Hexmags, so the magazines shouldn't be the problem. I'm hoping I can smooth out some high points to remedy this issue.

Photos of completed gun for attention.

I would try different magazines before messing with buffer springs or feed ramps.

Tx-Ag2010 said:

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I would try different magazines before messing with buffer springs or feed ramps.

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I could see a different mag maybe having a different result in the bolt not locking back, but not on the shavings. I have some PMAGS, and some standard aluminum AR15 mags that I'll try.

OP, try different mags first. Second option after mags is to take a weight out of your buffer.

Drive the pin out holding in the nylon bumper at the back of the buffer, remove a weight and reassemble.

Thanks, I'll give it a try.

Get the 300BLK spring from Nemo Arms. Essential for shooting both subs and supers in the same gun.

tx4guns said:

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Get the 300BLK spring from Nemo Arms. Essential for shooting both subs and supers in the same gun.

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I've got one of these i need to get rid of, in case the OP is interested. Only ~100 rd's through it.

What's special about this spring?

The nicks are from the barrel extension. When the extractor pushes on one side, the case tilts and scrapes along the lugs of the barrel extension before ejecting all the way out.

It's a lighter spring, so it allows the rifle to cycle more reliably with lower powered loads, which is what the BLK is by nature.

Are you sure it's brass? It could be unburnt powder, or I have read of some ammo makers who use inert fillers that leave a mess in the upper, or could it be copper shavings coming through your gas systemthat I have experienced in my 300 blk.

As for the not locking back subs are intended to be suppressed, which increases back pressure and would likely lock back. If you want reliable lockback you could go with a lighter buffer, but that might cause double fires, you could go with the lighter spring or you could open up your gas port a bit I think I opened mine to 0.011" or 0.013" and it runs anything now.

Typical arfcom solutions would be: heavy buffer, full mass M-16 BCG, muzzel break (sic), adjustable gas block.

(All of the above will exacerbate tour problems)

Log, their webpage says the spring is for carbine length gas systems. I'm assuming it works in pistol length gas systems as well? Would this be in addition to removing a weight from the buffer?

Mr. Dubi said:

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Are you sure it's brass? It could be unburnt powder, or I have read of some ammo makers who use inert fillers that leave a mess in the upper, or could it be copper shavings coming through your gas systemthat I have experienced in my 300 blk.

As for the not locking back subs are intended to be suppressed, which increases back pressure and would likely lock back. If you want reliable lockback you could go with a lighter buffer, but that might cause double fires, you could go with the lighter spring or you could open up your gas port a bit I think I opened mine to 0.011" or 0.013" and it runs anything now.

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I assumed they were small flecks of brass. I could be completely wrong. One thing I remembered today was that I saw similar flecks in the chamber when I received the upper from PSA. It was a new upper. Do they test fire uppers? I just assumed it was some debris from packing components or assembly. I'm thinking I was way off there as well.

If copper shavings, is this something that will reduce with time as the barrel wears or is it just something that happens on a pistol length gas system?

Carbine and pistol buffer tubes are the same length. Just use a standard CAR buffer.

Pistol and CAR gas systems are different lengths, which may be a minor point of confusion.

Log said:

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Carbine and pistol buffer tubes are the same length. Just use a standard CAR buffer.

Pistol and CAR gas systems are different lengths, which may be a minor point of confusion.

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That's what confused me, as their webpage states Carbine GAS system.

I live in Ohio, how much you want for the spring?

Dubi, I went back and found a couple of specs I missed when cleaning it (found them under the dust cover hinge) and looked at them closer. Doesn't look like copper or brass. I'm guessing inert from the rounds. I only shot Hornady, American Gunner and Sub-x. Does Hornady use inerts in either of those?

$12; got it from Brownells for $15 and it only has ~100 rounds through it. You can definitely tell a difference between it and a standard CAR spring when you hand cycle the action. Much lighter. I was having tons of ejection issues until I started using it. But then I decided to tear that build down, so I don't need it anymore. PM me and we'll figure this out.

I can't PM, my email is rdgomez98 at gmail dot com.

OhAggie98 said:

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I intend to use the subsonic rounds for home defense.

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Mind if I ask why?

BenderRodriguez said:

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OhAggie98 said:

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I intend to use the subsonic rounds for home defense.

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Mind if I ask why?

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So the bad guys can't hear the bullets! Duh!

I can say that the new Hornady round is awesome. Put some pigs down this weekend with them. I don't think I'd rely on them for home defense, but they are lethal at 50-100 yards.

To minimize energy and possible over penetration of rounds leaving my house and going into the neighbors houses that are about 20 yds in either side of my house. I feel more comfortable that the plaster walls and brick exterior will stop them better than normal rounds. Am I thinking wrong?

Sent.

I don't know about who uses what for inerts. I haven't even shot my 300 blk in a couple years. I have noticed some loads tend to leave a similar residue in all of my SBR's. It seems to me the powders with the larger granules burn less completely. The powder that comes to mind first is Hodgdon 4198.

Your gun is too dry. Whenever someone at the range is having issues with a new build cycling the gun is always too dry. Don't put lube in the spots you're supposed to put lube. Use a spray lube and put it everywhere. Pull the bolt and spray it until it's dripping, spray the chamber and spray in the ejection port and spray up the magwell. Put a couple mags through it and see if you still have issues. If it does and you had built it I'd say check for gas block alignment and/or open up the gas port next, but since it sounds like a factory build I'd say the next step is to call the manufacturer and/or send it back

OhAggie98 said:

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To minimize energy and possible over penetration of rounds leaving my house and going into the neighbors houses that are about 20 yds in either side of my house. I feel more comfortable that the plaster walls and brick exterior will stop them better than normal rounds. Am I thinking wrong?

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From what I've been able to find, yes. I've been researching the same question because I have a similar living situation and have a 8.5" 300 blk I'd love to switch over to for HD.

Barrier penetration is counter intuitive to a lot of folks. 5.56 rounds will tend to tumble/lose velocity faster than even 9mm rounds, which is why I currently use a 14.5" (pinned to 16") AR in 5.56 as my HD gun.

Because of their speed and construction, from what I've been able to find subsonic 300 blk rounds are going to tend to penetrate intermediate barriers like drywall more than 5.56. Supersonic 300 blk also penetrates more than 5.56 (more mass in the bullet takes more to slow it down), but behaves better than subsonic. Supers also expand much more reliably than subs do, so effect on target would be much better using something like 110 gr V-Max over subsonic rounds.

For now, I'm sticking with the slightly longer 5.56 gun based on barrier penetration being a concern and not having enough info about 300 blk penetration through barriers. When I finally get out of here and don't have neighbors so close, I"ll probably switch over to the suppressed 300 blk...but likely running supers.

All that being said, most rifles will tend to over penetrate through barriers less than shotgun or pistols will, so if it was a pistol or a 300 blk (subs or supers), I'd take the 300 blk.

NRD09 said:

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Your gun is too dry. Whenever someone at the range is having issues with a new build cycling the gun is always too dry. Don't put lube in the spots you're supposed to put lube. Use a spray lube and put it everywhere. Pull the bolt and spray it until it's dripping, spray the chamber and spray in the ejection port and spray up the magwell. Put a couple mags through it and see if you still have issues. If it does and you had built it I'd say check for gas block alignment and/or open up the gas port next, but since it sounds like a factory build I'd say the next step is to call the manufacturer and/or send it back

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I used Seal 1 lubricant and had so much in it, the inside of the upper receiver was a sloppy mess. The brown you see was a discoloration of the lube that was all over the place. I think the discoloration was from the rough bolt carrier from PSA getting smoothed out after initial firing.

Bender, thanks for the insight. I'll have to look into it some more. The reason I was leaning towards the Hornady Sub-X rounds is their claim of expanding without issue at subsonic speeds. I need to look into them more and confirm if any independent tests have confirmed this claim.

Right now, I have my 9mm in the night stand. So maybe this might be better. However, from your research it sounds like I need to consider my .223 that's kept in the gun safe as my go-to home defense weapon, or buy a 5.56/.223 pistol upper for this one. Hmm, good excuse to buy something else. Lol

BenderRodriguez said:

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OhAggie98 said:

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I intend to use the subsonic rounds for home defense.

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Mind if I ask why?

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I use them so I don't wake the neighbors!

OhAggie98 said:

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To minimize energy and possible over penetration of rounds leaving my house and going into the neighbors houses that are about 20 yds in either side of my house. I feel more comfortable that the plaster walls and brick exterior will stop them better than normal rounds. Am I thinking wrong?

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I used to spend a lot of time looking at Brass Fetcher videos on Youtube after Bender's advice of using an AR for HD.

Brass Fetcher 300 blk sub gel test

Brass Fetcher 30p blk super gel test

Brass Fetcher M 193 gel test

I was just looking at different 300 blackout ballistics tests and articles. What are your thoughts on the Lehigh Defense 300 Blackout 78 grain "close quarters"?

LEHIGH DEFENSE 300 BLACKOUT 78 GRAIN "CLOSE QUARTERS"