RESOLVED, BUT NOT FIXED: Stuck BCG along with short stroke issue 300 blk carbine length

TC.TURTLECREEK

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Apr 24, 2021
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Tennessee
I hav shot ARs for years, but just recently built my first upper. My issue is:

1. It is not ejecting casing. (short stroke) it it doesn't lock open on final round. it cycles fine and locks manually.
2. With suppressor, it did actually eject between 2-3 oclock
3. all other efforts (unsupressed) were either ejected, but didn't feed, didn't eject or jammed.
4. ammo is 2000fps 150g fiocchi. i have no issue with them on my other 300 blk (9" pistol)

as you may have guessed, it is a 300 blk. I was given a wilson combat barrel, 16" w/ carbine length. I have put SA adjustable block. I followed procedure and have it wide open. I moved it between two lowers, one a factory colt and the other, one i built with a brace. buffer was 3.0 and 3.8 on the two of them. the BCG is a semi-auto from Palmetto. It locks/unlocks fine.

two other BCGs that are boron coated that I have used on the other rifles tend to lock up and I need to hammer on it, but once it unlocks, they come out without issue.
the upper is an enhanced aero precision.

questions:

1. is there a break in period, so i should just shoot 100+ rounds suppressed to make it cycle (hopefully) and then see what happens?
2. should i lube the crap out of everything to facility this breakin?
3. any ideas on why some BCGs lock up and some don't?
4. even though the palmetto arms one doesn't lock up, it doesn't feed regularly, as stated above.

thanks for your help.
 

Milf Dots

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Eliminate the can while troubleshooting the gun. Start with the gas block in one position and document any changes as you adjust it.
 

st1650

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You’re most likely under gassed or oversprung for a 16in. Or you didn’t align the gas block properly and you’re not getting all the gas when it’s wide open.

If it’s not the gas block then you can try a lighter weight buffer/spring combo or a lightweight BCG.
 

TC.TURTLECREEK

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Apr 24, 2021
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Eliminate the can while troubleshooting the gun. Start with the gas block in one position and document any changes as you adjust it.
thanks. i started with no can. 18.5 clicks is max open. after that, you are closing off or bleeding off. what changes should i be trying besides gas block adjustment?
 

TC.TURTLECREEK

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Apr 24, 2021
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You’re most likely under gassed or oversprung for a 16in. Or you didn’t align the gas block properly and you’re not getting all the gas when it’s wide open.

If it’s not the gas block then you can try a lighter weight buffer/spring combo or a lightweight BCG.
ok, so i thought lighter might be better, but wasn't sure. i'll buy some lighter buffers. any thoughts on the locked bcg?
 

Milf Dots

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Check out these five linked articles for help. And, are you sure it's undergassed? It's actually more common for ARs to be overgassed, and overgas can mimic some of the symptoms of undergassed rifles.



 
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TC.TURTLECREEK

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Apr 24, 2021
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Check out these five linked articles for help. And, are you sure it's undergassed? It's actually more common for ARs to be overgassed, and overgas can mimic some of the symptoms of undergassed rifles.



thanks for this. the stuck BCG is an off center gas tube along with the fact that the boron coated BCGs seem to have gas keys that are further from the center of the BCG...maybe 30 thou? i pushed the gas tube up a little with my finger and now the original semi auto BCG drops in fine and one of the boron BCGs drops in fine. The other is still "sticky", but i don't need it to work, so I'm not worried about it. i am intrigued to go to the range and see if something like this caused my issue. as the semi-auto BCG didn't feel like it was sticky, I'm guessing this alone won't fix it, but its a start.
 

TC.TURTLECREEK

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so i went to the indoor range with all the parts i have. i swapped buffers, BCGs and magazines. it never locked back. i threw the suppressor on it and supers would lock back. so i am guessing undergassed. this was all with the fiocchi 150g that I have shot without issue in my 9" pistol 300 blk. i happened to have 125 SST w/ CFE BLK and 150g Hornady with the same that i reloaded for my pistol. so i tried them and BAM....locked out everytime on final round. this is a hunting barrel, so i will never need to shoot 150g fiocchi out of it. as a matter of fact, i will be shooting the 125 SST or a 110 TAC-X from it with CFE BLK for hogs/deer. so, it appears as if i am undergassed with a round i don't need it to work with. i dont like the fat it won't shoot all supers. i have never had a gun that wouldn't shoot whatever i put in it. that being said, i am sold on pistol length gas. it eats supers, subs, unsupressed or suppressed.... thanks for the help.
 

st1650

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Make sense, CFE BLK is a slow powder and will generate more gas than your usual H110/W296, etc
 

hlee

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    Yeah, my 300 blk out doesn’t lock back with some flavors of factory ammunition. So I don’t shoot that ammunition…
     
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    tomme boy

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    Take your bcg out of the receiver. Put a drop of oil into the gas key. Take compressed air and blow into the gas key. Hopefully you have a rubber tipped blow gun. Look to see if oil comes out under the gas key and carrier. If it does you need to take it apart and put on some of the correct sealant between the 2. Most manufacturers do not do this. But it is required according to milspec. It takes up the differences in the machined surfaces.
     
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    jsjac

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    Check out these five linked articles for help. And, are you sure it's undergassed? It's actually more common for ARs to be overgassed, and overgas can mimic some of the symptoms of undergassed rifles.