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10.5 AR jams on 55g but not 62g

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So I have a 10.5 AR pistol and whenever I shoot 62g green tips it functions flawlessly.
But with brass 55g 223 it inconsistently jams.
What happens is it fails to eject the shell on the 55g ammo and jams but it's inconsistent..
I am on a after market 3.5lb trigger but it did this on a mil spec trigger aswell.
Any ideas?
 
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nwslopoke

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So I have a 10.5 AR pistol and whenever I shoot 62g green tips it functions flawlessly.
But with 55g 223 it jams.
Any ideas?
When you say jams, can you expand? Fires 3 rounds then fails to feed? Are you using brass ammo? Are you using a mil spec or modified trigger? Ect. A little more info will help.
 
OP
draza
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The first thing I would do is try a different batch (or two) of 55gr loads to rule out a bad lot of ammo. If it short cycles with all 55gr ammo, I would try a lighter buffer.
I am on a regular carbine buffer weight and I have tried Federal 223 brass and a mixed batch of brass 55g 223 I got in a trade from someone.
 
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Pinned gas block, or screw-on ?
Gas block seated correctly ?
Any sign of leakage around the block / barrel ?

Also, a lot of pistol length barrels on the market are clipped carbine barrels with an incorrect port for the shorter length.
 

DirectDrive

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I am on a regular carbine buffer weight and I have tried Federal 223 brass and a mixed batch of brass 55g 223 I got in a trade from someone.
Civilian .223 is loaded to lower pressures than 5.56 ammo.
Makes me wonder if it will run Lake City XM193 (5.56 55gr) ?

A Reduced Power (RP) buffer spring might work for that .223 ammo, if you intend to shoot a lot of it.
Out of curiosity, I would try some XM193 (widely available) in it first.

With the AR pistol (non-blowback), "dwell" is very short.
"Dwell" is the amount of time that the gas system is pressurized.
A given pistol that runs on full power ammo may not run on weak ammo unless tuning adjustments are made.
Here's a pic that shows the various gas system lengths.
Dwell is directly related to the length of barrel AFTER the gas port.
AR-15-Barrel-Contours_d400.png
 
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nwslopoke

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I had is similar issue with my 7.62x39 AR15 using steel cased ammo and too light of a trigger. Apparently in my case the hammer was not striking hard enough as I had feared with the lighter trigger springs. It would fail to eject because the bolt was not returning with enough force to strip the next round. I put the mil spec trigger back in and the problem went away. I don't think this is your problem.

Being a pistol I would swap the buffer or BCG if you have another rifle. I have a 10.5 pistol using a standard buffer, a commercial BCG (non M16) and a 2 stage trigger. It's a PSA Franken gun but no issues.
 
Civilian .223 is loaded to lower pressures than 5.56 ammo.
Makes me wonder if it will run Lake City XM193 (5.56 55gr) ?

A Reduced Power (RP) buffer spring might work for that .223 ammo, if you intend to shoot a lot of it.
Out of curiosity, I would try some XM193 (widely available) in it first.

With the AR pistol (non-blowback), "dwell" is very short.
"Dwell" is the amount of time that the gas system is pressurized.
A given pistol that runs on full power ammo may not run on weak ammo unless tuning adjustments are made.
Here's a pic that shows the various gas system lengths.
Dwell is directly related to the length of barrel AFTER the gas port.
View attachment 620741


^^^THIS^^^


.223 will produce a different brass ejection pattern than 5.56... run 5.56. This is also why the barrels in USGI CAR-15’s aren’t under 11.5” because of dwell time, and .223 can exacerbate the issue. Having the size of the gas port increased may help the situation.

From day one my two 80% build 11.5” pistols have eaten everything I’ve fed them without any issues, and it’s all MILSPEC innards with the exception of the KNS dog-bone retainers.

C69C5F33-7962-4D61-A825-E70C1D0BAC3B.jpeg
 
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DirectDrive

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I urge any newly minted Kitchen Table Gun Plumber to exhaust all options before drilling out the barrel's gas port.
The "go-back" is not easy on that one.

ETA:
I suppose if the gas port was punched out to run weak .223 ammo, you could install an adjustable gas block for running full power military ammo.
Not my cup o' tea though. I feed 'em and tune 'em to run full power ammo.
 
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Check size first, of course.
My first thought was a small gas port.
If it needed, I'd bore it larger and throttle back with adj GB.
Then focus on buffer spring and buffer for finals.
I've never had issues without resolve, yet.
I'll be messing with a 7.5" wylde 223 toy soon.
 

gprippers

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223 IS LIGHTER LOAD THEN THE MIL 62 GRN. WHEN YOU GET SHORTER THEN BARE MINIMUM 11.5 BARREL YOU NEED TO MAKE SURE YOU ARENT OVER GASSING JUST AS MUCH AS UNDER GASSING. THE VIETNAM ERA GUNS, "COMMANDO CARBINES" FAILED TO WORK CONSISTENTLY SO THEY PUT THOSE SHORTY BARRELS ON WITH THE 5 INCH FLASH SUPPRESSORS TO GET THEM GOING.

BUT WITH WHAT YOU ARE DESCRIBING, ITS PROBABLY AN UNDER GASSING ISSUE. TRY SOME 5.56 MILITARY LOADS AND THAT WILL ANSWER YOUR QUESTION. YOU MIGHT JUST HAVE LIGHTER 223 LOADS. IF ITS AN OVER GAS, WHICH I DOUBT BASED ON YOUR DESCRIPTION, YOU CAN TRY DIFFERENT GAS BLOCK OR PIG TAIL GAS TUBE. REALLY THINK ITS LIGHTER CIVI 223 LOADS THOUGH.

I HAD A CLASS 3 SHORTY THAT I HAD TO PUT A PIG TAIL GAS TUBE IN TO GET IT TO FUNCTION PROPERLY. PIG TAIL TUBES HELP WITH THE OVER GASSING YOU GET IN THE SHORTER TOPS.
 
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Jcon268

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A lot of the problems with ARs not running properly stems from improperly spec'd gas ports. Most gas port issues can be tuned with a combination of buffer adjustment although not always. Ideally, your AR should eat any .223 or 5.56 NATO ammo you throw at it. My 10.5" SOLGW build eats any type of ammo and that's suppressed or not suppressed.

Best thing to start with is find out who mfg. the barrel is and get the gas port specs (preferablly directly from the mfg) and figure out if you're over-gassed or not. Most barrels tend to err on the over-gassed side.
I'd highly recommend looking into a VLTOR A5 buffer system. Most guys throwing these on their builds have gotten rid of any problems running they might have had before.
 

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