my 300 blk eats its own poo

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308loader
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my 300 blk eats its own poo

Post by 308loader » Tue May 28, 2019 7:40 pm

It has been long known that the AR15 poops from where it feeds, meaning it expels dirty gasses into the BCG. I recently built an 16" upper with pistol length gas system that will eat the case it pooped out. By that I mean, the round fires, strips a new round from the mag and almost chambers it when either the case head or mouth of the spent round is reintroduced to the action, blocking the bolt from going into batterie. This happens with box ammo and reloads of all sorts bullet weights and velocity's. I read somewhere to work on the back of a 300 blk first, then work out the front end for reliability.

Any one ever have this problem? when I run the same BCG and lower in 223/556 upper I have no issues, in fact it is the best 223/556 I have... its almost like I am missing short of the brass deflector and bouncing back into the action.

Any thoughts appreciated :)

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dellet
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Re: my 300 blk eats its own poo

Post by dellet » Tue May 28, 2019 10:04 pm

Without knowing the exacts specs of buffer weights, spring, carrier style, possibly gas port size it’s hard to say. But the first thought is way over gassed. Pistol gas in a 16” barrel is asking for trouble and gets worse with a suppressor.
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wildfowler
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Re: my 300 blk eats its own poo

Post by wildfowler » Tue May 28, 2019 10:38 pm

Are you using a brass catcher? Or have an unusually large scope mount?

I’ve have issues from these things in the past that turned out to be the last place I thought to look. Literally.

If you’re unsure, completely remove these items to test?

Edit:

Also, try the “slow motion” video setting on your phone to make a video you can review.
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GunFunZS
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Re: my 300 blk eats its own poo

Post by GunFunZS » Wed May 29, 2019 8:06 pm

Check:
1) Ejector
2) Extractor
3)gas rings
4) That you have an H2 or heavier buffer.
5) figure out whether you have a standard weight buffer spring.

308loader
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Re: my 300 blk eats its own poo

Post by 308loader » Thu May 30, 2019 6:05 pm

tried posting a lengthy response, it got lost in cyber space. is windows browser edge not supported? keeps telling me "checking browser" and logs me out.

308loader
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Re: my 300 blk eats its own poo

Post by 308loader » Thu May 30, 2019 6:08 pm

well that worked …. will type up in another format and copy paste I guess. must be a timer or some thing. while I type fast, how do you post images and vid here? third party?

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dellet
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Re: my 300 blk eats its own poo

Post by dellet » Thu May 30, 2019 6:22 pm

There have been some huge spam issues and the browser check is the latest attempt to stop that. Hopefully it gets better.

If you type out a response, before leaving the page, copy everything in the box so you can paste it if it disappears. I "copy" then hit preview. If it drops re-open and paste the text. Second option is before leaving the reply page, open a second window and make sure you're still logged in. Either way copy your text just in case. It's a colossal pain in the ass but better than 6 pages of spam everyday.

Photos and video need to be hosted on another site and linked.
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Re: my 300 blk eats its own poo

Post by rebel » Thu May 30, 2019 9:25 pm

dellet wrote:
Tue May 28, 2019 10:04 pm
Without knowing the exacts specs of buffer weights, spring, carrier style, possibly gas port size it’s hard to say. But the first thought is way over gassed. Pistol gas in a 16” barrel is asking for trouble and gets worse with a suppressor.
+ 100
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BoomerVF14
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Re: my 300 blk eats its own poo

Post by BoomerVF14 » Sat Jun 01, 2019 8:39 am

Assuming you're having this problem with supers... yes? Does it also accur with subs?

Building on dellet's diagnosis, I'd turn your adjustable gas block all the way to zero and start testing by opening it in small increments until the action cycles. If you're still getting stoppages then it might be worth checking the ejector/extractor, but you said it works fine in your 5.56 so I'd be surprised if that's the case. Get the gas metered properly before fine-tuning springs and buffers.

You DID build your 16" pistol gas upper with an AGB, right? :shock:

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Re: my 300 blk eats its own poo

Post by 308loader » Tue Jun 04, 2019 6:40 pm

so here is the short story on the 300 blackout build. my shop mechanic sold me this barrel for $40, said he had no use for 300blk. built the cheapest upper I could put tougher because I too really have no use for the blackout but wanted to give it a go. By no real use for 300 blk I mean, I don't own a suppressor and have plenty of other rifles that fit the 30 cal bill, sounded like a fun project. upper is no name gun show purchase ($40 or less new), hand guard is $40 on sale key mod with steel barrel nut. barrel if I had to guess is a PSA, markings look the same as another PSA I have. gas block is ZHmgb02a micro, (not AGB). gas tube is pistol length, standard bird cage on the muzzle. Lower is from Olympic flat top plinker (?) 556 16" carbine, has commercial spec buffer tube and what ever buffer and springs it came with. the poo eating happens with all velocity's randomly. seems more stable in the mid range, still will catch one in the receiver from time to time (1 in 10?). Ran the same upper on my Anderson lower and A2 stock and found a different issue. same upper same bolt same mag. this time it would lock open like an empty mag after every shot. no poo eating, but have to drop the bolt every time (one point for the BAD lever).

I've run ladders with 5different bullets (125-180gr) and 2 different powders (H110-CFE blk) results seem to be the same.

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