AR-15 Buffer/Spring Combinations for Reliable Feeding and Lock Back

martinga111 · Mar 25, 2015

I just put together a 18" match upper to mate to an existing lower that performed flawlessly to date with a standard M4 Carbine upper.
Now with this new upper, I am not getting lock back and I had 3 FTE's in a row using M855 ammo.
Slower hand loads (~2800 fps) ran perfect and locked back 75% of the time.
It's not magazine related as they all worked fine on the carbine upper.
I was told in a match that I wasn't throwing the empties out as far as typical and iit was about 2 o'clock position.
I have an assortment of springs and buffers, but I don't know what the spring powers are and the buffers are either Standard or Heavy.
I have a spikes tactical powdered tungsten buffer, but it is not as heavy as a H2 buffer, sort of in between a H and H2 (4oz.)
I have a mid-length gas set up.
I've ordered 3 Wolf Gun springs in Std, XP and RP and a H2 buffer.

Anyone ever have this problem and any suggestions ?

charger arms · Mar 25, 2015

Is your gas block not over the gas port in the barrel correctly? Are your gas rings worn out?

martinga111 · Mar 25, 2015

The gas block is perfect and the BCG is brand new, rings are intact and functioning.

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SDUKES · Mar 25, 2015

Is the gas block adjustable?

charger arms · Mar 25, 2015

Only reason I was asking about the gas block is that I had to just feeler gauges to space mine properly over the undersized (on purpose) gas hole on the barrel. The gas block had to be set .03 in front of the shoulder to line up correctly. New gas block was shorter that A2 sight base and hand guard ring. Might be worth pulling out the calipers and double checking.

Wall · Mar 25, 2015

If its not an adjustable gas block, I'd bet the gas port on the barrel is too small

martinga111 · Mar 25, 2015

The gas block is a YHM Clamp on style. I checked the position of the gas block hole and barrel gas port and they were right on. I had a former Marine Armourer look at it and he thinks it's getting too much gas because of the mid length port location on the 18 barrel. I had a no name kit action spring and the lightest std. buffer. It also makes sense that it's getting too much gas because it would not lock back with hot ammo (>3000 fps), but would with 2800 fps hand loads. The problem is I need the hotter ammo to move flashers out to 300 yds in 3 gun matches. I was just wondering if anyone had experience with this and if different springs and or buffers solved the problem.

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technetium-99m · Mar 25, 2015

If you are sure the block and carrier are good then the gun may be running too fast.

I had an 18" mid length barrel that was a major PITA to get reliable with low mass components. I eventually gave up and went with a different barrel. Are you seeing any double feeds or any cases with the rim ripped off?

Put a new buffer spring in with a heavy buffer and see if it gets better, or put on an adjustable block and see if throttling back on the gas helps.

Wall · Mar 25, 2015

put on an adjustable block and see if throttling back on the gas helps.

This

Matt1911 · Mar 25, 2015

I know a guy who sells adjustable gas blocks.

martinga111 · Mar 25, 2015

technetium-99m said:
If you are sure the block and carrier are good then the gun may be running too fast.

I had an 18" mid length barrel that was a major PITA to get reliable with low mass components. I eventually gave up and went with a different barrel. Are you seeing any double feeds or any cases with the rim ripped off?

Put a new buffer spring in with a heavy buffer and see if it gets better, or put on an adjustable block and see if throttling back on the gas helps.

No double feeds or rim rips. I was going to try a H2 buffer and either a standard or XP spring. All are on order and should have this week.