Short AR's cycling problem WHAT TO DO

corrantum25

corrantum25

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Hi dear pals

here my problem

i have a Bushmaster 11.5 and it work very well with any kind of ammo
i just bought a LMT 7.5 upper for xmas
i try it yesterday at the range with the bushmaster 11.5 bolt assem and buffer and the new ar combination jammed

i was able to shoot only 10 rounds correctly after that the gun jammed each fu... round i shoot

the first round is fine but the gun cannot feed the second round in the mag
it extract the empty brass correctly but the bolt didnt go rearward enough to take the fresh round

maybe its a bad buffer combination
i shot with some UMC and Korean 55grains

may you tell me what i have to do to solve the problem

Regards
Chevy

each time it extract the empty brass and didnt feed the next one so i have the bad surprise of the CLICK (empty chamber)
 
Make sure that gas block or FSB is properly lined up with gas port.

Make sure you don't have a bad magazine.

If the ammo cycles fine in other guns, then you can rule out bad ammo.

If all of the above checks out, try switching to a heavier buffer and/or full auto bolt carrier. If you are using a standard weight carbine buffer and semi-auto carrier, they might not be doing the job with what they have to work with on the 7.5" gas system.

I run an H buffer and full-auto carrier in one shorty that had cycling problems before the changes. Now works like a charm.

Another I ended up going with an H2 and full-auto carrier. It runs like a top now.

For the other (an 11.5") just an H buffer and standard semi-auto carrier was enough to ensure 100% reliability.

You might need to try different combos to find the right one that will work with your rifle. Oh, and make sure you have the right length of spring as well! Don't break out the dremel tool and drill out your gas port!
 
Obstruction in the gas tube ... misaligned gas port with the front sight tower ... incorrect gas post size in the barrel ...

Maybe your bolt and carrier is bouncing erratically under violent reciprocation where a heavier carrier and/or heavier buffer could help by slowing down the action.

Check your gas key atop the carrier too, with improper staking, it may get loose. May have worked for your Bushy upper but hiccups with the 7.5".

Enlarging the gas port is the extreme last thing I'd attempt. With that in mind, I know there have been some 7.5" barrels made by somebody or other that had an incorrect port size drilled right out of the factory.

... and yeah, no 7.5" uppers in the LMT line-up. The upper no doubt, but not with a 7.5" barrel. You got something else. Examine the barrel for markings.

Happy Ho, Ho Season and good luck getting it going.
 
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easy said:
Obstruction in the gas tube ... misaligned gas port with the front sight tower ... incorrect gas post size in the barrel ...

Maybe your bolt and carrier is bouncing erratically under violent reciprocation where a heavier carrier and/or heavier buffer could help by slowing down the action.

Check your gas key atop the carrier too, with improper staking, it may get loose, May have worked for your Bushy upper but hiccups with the 7.5".

Enlarging the gas port is the extreme last thing I'd attempt. With that in mind, I know there have been some 7.5" barrels made by somebody or other that had an incorrect post size drilled right out of the factory.

... and yeah, no 7.5" uppers in the LMT line-up. The upper no doubt, but not with a 7.5" barrel. You got something else. Examine the barrel for markings.

Happy Ho, Ho Season and good luck getting it going.
Click to expand...

Good advice here too!
 
99% of the time the problem with short barreled ARs can be cured with the addition of a heavier buffer and/or a full auto bolt carrier, you have to slow down the gas impulse,changing the gas port size is an unnecessary step in most cases.
 
Short stroking

I had every standard fix (port lined up,H buffer etc.etc.) on a shorty that short stroked just enough for the bolt to catch after the last round, but not all the way (with factory commercial ammo). It was fine with current mil-spec.
Cheap ammo is the way to go -

SO-

I cured it by cutting 2 1/2 coils off the buffer spring. Buffer springs are cheap, and no ill effects after many thousands of rounds.
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Also if you built it your self, you may want to make sure you used a M4 upper with a M4 feed ramped barrel.
 
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