AR15 Pistol only shots 5.56

[kenjazz59]

I'm new to ARs. Got 2 7.5" AR15 Pistols within the last 30 days. Bought one used and the other new. Both supposedly had 200 rounds through them. They both will only shoot 5.56 without any problems. I get FTEs after the first round of .223s are fired. I load only 25rds in 30rds Magpul G2&G3s. Cleaned & lubed per recommendations given by numerous YouTube experts. I did a Google search and didn't find similar problems. Could this be a buffer spring issue.

TIA,
Ken

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[gaijin]

Check buffer (H1/H2/H3?), gas port, maybe buffer spring.

The short answer; if it shoots 5.56 flawlessly, shoot 5.56 exclusively.

[ColtSeavers]

As mentioned above, what weight buffers are in them? Are they using standard carbine springs or some aftermarket ones?

Replace buffers and springs with standard carbine ones. Increase carbine buffer weight until you experience problems with the weakest ammo you plan to shoot (magazine using standard carbine 3oz. weight, if it functions as it should, repeat with fresh magazine and H1 3.8oz. buffer next, etc.)

Speaking of magazines, are you 100% postive the magazines you are using are gtg?


After you find what the heaviest buffer each one likes is, then you can worry about upgrading the carbine springs in each (Sprinco) if you further desire to mess with them to further tame recoil/fine tune cycling.

[Wake27]

I didn't even know there were 7.5" guns in 5.56. I thought the shortest anyone went was 10.3 unless they were using 300 BO or something else.

[kenjazz59]

Gaijin/ColtSeavers, thanks for advice. The pistol shoots. 223s well when I use the T2 buffer from my Spike's rifle. So, I'll be shooting 5.56 until the new T2 arrives.

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[chrischoi]

Probably overgassed. Have you just shot it with a standard weight buffer?

[kenjazz59]

Yes, I originally started with a standard weight buffer. Also, the STT2 experiment failed after 100 rds. I'm going to try the Bootleg adjustable BCG next.

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[MistWolf]

If it shoots 5.56 well, but chokes on 223 supposed ammo, it's not over gassed. If it's not over gassed, an adjustable BCG won't help.

When you say "FTE", what exactly do you mean?

[Lincoln7]

Check your gas key screws and the tightness/position of your gas block. I had an AR that was not locking back on last round with only Wolf ammo. Cycled fine though, and all 5.56 ammo was locking back properly. My gas block screws were still tight but it had shifted forward a fraction. Repositioned it and it worked great again. I promptly dimpled the barrel for the GB and it's been great since.

[kenjazz59]

If it shoots 5.56 well, but chokes on 223 supposed ammo, it's not over gassed. If it's not over gassed, an adjustable BCG won't help.

When you say "FTE", what exactly do you mean?

Spent casing isn't ejecting. Appears gun isn't cycling. I'm thinking it's a underage problem.? Gas block seems to be in over barrel hole. Gas line seems clear of obstruction.

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