*UPDATE* Disappointing outcome - first time out with .308 build

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Originally Posted by 1168

Carrier key screws?

I only personally know of one rifle where a gas port on a reputable barrel truly had to be opened (and wasn’t made that way on purpose). It was a .224 Valk using a high-end barrel. Short stroked, so the owner dumped the weights out of the (rifle length) buffer, and it cycled. Barrel maker warrantied it and opened the port.

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I know of many including 3 from this manufacturer.

I'm finding it difficult to reconcile the rifle locking back on empty (indicating sufficient gas drive) and needing the gas port opened up. Your problem may be magazine or ammo related.

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Originally Posted by georgeib

I'm finding it difficult to reconcile the rifle locking back on empty (indicating sufficient gas drive) and needing the gas port opened up. Your problem may be magazine or ammo related.

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George it locks back on an empty mag using the charging handle, it will not lock back on an empty mag when fired

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Originally Posted by Black_Sheep

George it locks back on an empty mag using the charging handle, it will not lock back on an empty mag when fired

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Ahh. Got it now.

Still inclined to think that the gas port size is sufficient. Mine has a 0.080 on a mid-length 18" barrel, and I had to use an adjustable gas block almost completely closed to tame the over gassing. Even with cheaper brass cased ammo. Is there someone you can borrow a BCG from to test?

Interesting everybody thinks 075 intermediate 308 is perfectly fine.

It's certainly possible the NiB BCG is the issue.

The gas key diameter and bolt tail seal diameter should be checked.

Also, the BCG could be swapped for a known good unit.

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Originally Posted by Clint

Interesting everybody thinks 075 intermediate 308 is perfectly fine.

It's certainly possible the NiB BCG is the issue.

The gas key diameter and bolt tail seal diameter should be checked.

Also, the BCG could be swapped for a known good unit.

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No access to another BCG but I can certainly measure the gas key and bolt tail seal diameters with a dial caliper. What kind of clearance would be considered acceptable?

Dial calipers are not sufficient.

Pin gauges are required for accurate ID measurement.

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Originally Posted by Black_Sheep

No access to another BCG but I can certainly measure the gas key and bolt tail seal diameters with a dial caliper. What kind of clearance would be considered acceptable?

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Double tap

Got back to the range tonight after making some changes to my carbine’s gas and buffer system. I’m relieved to report it runs as it should and reliably locks the bolt back on an empty mag. To fix it, I enlarged the barrel gas port with a #44 drill (.086) and swapped the Aero 3.8 ounce buffer and spring for one of Slash’s 5.5 ounce SS buffers and proprietary springs. The gurus over at the 308 AR forum were a tremendous help.

I had a few issues with my 308 build when I first put it together. I could lock the bolt back with the charging handle, but it would not reliably lock back while shooting. It all came back to an incorrect buffer and spring in the buffer tube. That’s where I would look first.


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