UMC ammo: not cycling without suppressor. Any ideas?

Discussion about rifles in 300 AAC BLACKOUT (7.62x35mm), hosted by the creator of the cartridge.

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9mmkungfu
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UMC ammo: not cycling without suppressor. Any ideas?

Post by 9mmkungfu »

Hi all,

First, let me give you specs on the SBR:

Noveske 8" 300 BLK barrel
Carbine buffer (H2 would not cycle)
Carbine spring
20rd Pmags
30rd Pmags (Rev M)

I've been shooting 220 gr subs with no issues (suppressed). The gun will not cycle without the suppressor (as Noveske designed their port this way).

I picked up two boxes of the newer UMC 115gr stuff this past week. It cycles fine with the suppressor (expected). However, it did NOT cycle properly unsuppressed.

The empty shell casing is not fully extracted from the chamber and a new round is wedged underneath, sitting on the feed ramp. I should have taken a picture but they don't allow cameras on the range where I was shooting. Looks like a double feed I guess.

Any thoughts on why? I thought the supersonic stuff was supposed to be ok to shoot without a suppressor.

Sorry if this has been discussed already. I haven't been keeping up with the 300 BLK stuff like I used to.
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chrismartin
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Re: UMC ammo: not cycling without suppressor. Any ideas?

Post by chrismartin »

Try a different bolt carrier group?
Double check gas block and gas tube alignment?
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AFMech
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Re: UMC ammo: not cycling without suppressor. Any ideas?

Post by AFMech »

Would'nt be gas block allignment as Noveskes are alligned and pinned in place from the factory. Might be a weak extractor spring if the brass is still sitting partially in the chamber. Like CM said, I would try another proven BCG before getting too upset.
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burton
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Re: UMC ammo: not cycling without suppressor. Any ideas?

Post by burton »

check for extractor spring o-ring.

my 8" Noveske has a similar issue successfully extracting 147 gr. ammo...turns out the bolt didn't have the o-ring.

once the o-ring was installed, extraction was flawless.
9mmkungfu
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Re: UMC ammo: not cycling without suppressor. Any ideas?

Post by 9mmkungfu »

Thanks for the replies. Unfortunately I don't have a spare BCG handy at the moment to test with, but I will soon.

I'm pretty sure I installed the gas block and gas tube myself last year when I put it together. This may have been before they started doing it themselves prior to shipping. It was one of their first 8" 300 BLK barrels.

In any case it works perfectly except for that one scenario: unsuppressed, with 115gr UMC.

I'll look for the o-ring first then try another BCG if that fails.

ETA: Answered my own question.

Thanks guys.
-k-
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Re: UMC ammo: not cycling without suppressor. Any ideas?

Post by -k- »

Load one round in the mag and check for bolt lock. Try it with a few different mags.

It sound more like a problem with your extractor or ejector. Check the ejector for binding, and check the extractor for damage. Make sure to use a standard rifle extractor spring with o-ring (best), or just the extra power extractor spring (check and replace every 3-5k).
Todd
imyomama
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Re: UMC ammo: not cycling without suppressor. Any ideas?

Post by imyomama »

based on what you said "h2 buffer won't cycle " and unsuppressed won't cycle .. you're slightly undergassed. this is most likely due to either a bad alignment of gas tube vs gas hole , or you could have your gas key coming loose. i'd check those first.

if all checks out , try lubing your bcg more if it's dry and you can also lube inside the buffer tube ... i've seen that help some times (plus it makes it a little quieter to the ear ...)
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9mmkungfu
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Re: UMC ammo: not cycling without suppressor. Any ideas?

Post by 9mmkungfu »

Thanks again for all of the helpful replies.

Todd - the bolt does lock back after firing all of the rounds in the mag but I have not tested with a single round. I will try that later this week.

It may be two issues. Slightly undergassed (H2 buffer will not cycle, suppressed) and the extractor/ejector.

I ordered a BCM extractor upgrade kit.

I will also lube the buffer tube. To be honest, it has never been lubed. I'll report back once I get some more troubleshooting done. I just haven't had the time due to work.

I do have a question. If it is indeed an extractor issue, why does it function fine with the suppressor on? Does the increased pressure mask the potential weak extractor issue?
9mmkungfu
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Re: UMC ammo: not cycling without suppressor. Any ideas?

Post by 9mmkungfu »

Update: I installed the BCM extractor upgrade kit (spring + o-ring) in my bolt and it has seemed to cure the problem. I ran about three to four mags through it yesterday without a hitch, although the Pmags don't seem to be 100%.

Thanks to all of you for your suggestions.

On a side note, go pick up some of the UMC ammo if you haven't already!
piperpilot3tk
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Re: UMC ammo: not cycling without suppressor. Any ideas?

Post by piperpilot3tk »

I shot my 300 BLK SBR for the first time this weekend and mine did the same thing. It would not extract the cases and would malfunction every two or three rounds. With the suppressor would cycle 100 percent. I have a Fail Zero bolt carrier assembly and a AAC 9" barrel. I took the extractor apart and found that it did not have a spring buffer or O-ring installed, and I could move the extractor easily with the tip of my index finger. I have a BCM extractor upgrade kit on the way and I feel confident that this will solve my problem.

Shooting the rifle was awesome and it was actually more fun than I expected! You can watch youtube videos of people shooting a suppressed 300 Blackout all day long, but you cannot really get an idea of how quiet and smooth the rifle is untill you shoot it for yourself. Those big 220 grain SMKs really make a loud thump when they hit the berm!
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