FTE with supersonics - what next?

[Bodie1331]

Newbie here - I have a an AR Stoner 10.5 barrel with pistol length gas system - Auto BCG, carbine length buffer tube and I can't get this thing to cycle supersonics without about 20% FTE.

What I've tried so far -

-1 coil buffer spring
Standard carbine length buffer spring
T2 Buffer
Sloppy wet BCG
USGI Mag
PMAG
Checked brass case neck thickness - (All at or under .012)
Checked gas block - port has symmetrical carbon around it and would seem properly aligned
Have tried H110 with 145 m80 from 15.5 through 17.0 without change in FTE rate.

Thy present like a bolt that has short cycled - the empty jammed into the feeding area just above the partially chambered live round.

All 208gr subsonic function flawlessly - What do I need to consider next? Boring the gas port? Very frustrated and want to shoot supersonic with much more regularity than subsonic - I don't use a suppressor and likely won't ever with this weapon. Thanks in advance!

[themonk]

What other weight buffer have you tried other than T2?

[Bodie1331]

Only the standard carbine buffer - I suppose it's an H?

[Bodie1331]

I should mention this problem persists with factory ammo as well --- Is it possible that it's over-gassed? If it's picking up another round it's surely not short cycling - maybe just a bad extractor O-ring? The BCG has less than 500 on it though.

[dellet]

Newbie here - I have a an AR Stoner 10.5 barrel with pistol length gas system - Auto BCG, carbine length buffer tube and I can't get this thing to cycle supersonics without about 20% FTE.

What I've tried so far -

-1 coil buffer spring
Standard carbine length buffer spring
T2 Buffer
Sloppy wet BCG
USGI Mag
PMAG
Checked brass case neck thickness - (All at or under .012)
Checked gas block - port has symmetrical carbon around it and would seem properly aligned
Have tried H110 with 145 m80 from 15.5 through 17.0 without change in FTE rate.

Thy present like a bolt that has short cycled - the empty jammed into the feeding area just above the partially chambered live round.

All 208gr subsonic function flawlessly - What do I need to consider next? Boring the gas port? Very frustrated and want to shoot supersonic with much more regularity than subsonic - I don't use a suppressor and likely won't ever with this weapon. Thanks in advance!

Since you cycle correctly with subsonic, there is a good chance that you are cycling too fast with the supers. Seems like what you have tried is to make it go faster with the cut spring and such. Maybe try slowing it down some.

Your loads are on the higher end, Hornady lists 15.9 as a max load for a 150 grain, Hodgdon 16.2. Since it is only happening 20% of the time it could be you are on the edge of what your setup will run, backing off to 15 grains is cheep and will answer if this is the right direction.
Knowing your col. would also help.

The recommended buffer is an H2, which weighs 4.6 ounces. If you can weigh your buffers. The ST2 weighs slightly less at 4.3, the H buffer would be lighter yet at 3.8. It is also possible that you have a standard carbine buffer at 3.0.

Spring should be standard carbine.

Finally check your gas port size. I think enlarging would probably be a mistake before you know your spring and buffer system are correct. Here is a discussion on pistol port sizes if you have not seen it.
viewtopic.php?f=128&t=87128

Have you possibly ran any factory supers? successful or not.
Did you use a chrono and know the speeds of either of the loads you shot?

[Bodie1331]

Okay - problem is solved -

put T2 buffer back in - upgraded the extractor with O-ring and now it cycles 145gr with 16.4 gr. H110 and 150gr Sierra spire point with 17gr H110 without any FTE.

145's (M80) where loaded to an OAL of 2.133 which should be keeping away from a compressed load -

I think that if I had just backed off the charges and slowed down the cycle rate some that would have indeed fixed the problem as suggested.

I have not chrono'd the loads but hope to in near future