I had this one BCG that keep bending the gas rings. It would work for a while and then all of a sudden a ring would jump out of the groove and jam the bolt.
I have been pouring over on-line drawings trying to figure out which dimension was off and how to measure it without a depth gauge micrometer. Finally finally figured out how to prove what was wrong and which dimension it is.
Both bolts are slowly lowered into the carrier until they are held in place by the rings just before the rings are squeeze into their "cylinder". Uh - oh. There's a significant difference in how far down the "cylinder" starts.
That difference means that when the bolt is full forward (out of battery) the rings are not fully inside their cylinder. The one on the left is too far down into the carrier. And as the bolt is locked, pushed back, the rings must re-engage that space. You could feel them if you operated the bolt with your fingers.
Here's a crude drawing of what I was trying to measure. (Don't laugh too hard at my drawing.) It represents the interior of the forward half of the bolt carrier. The slight, very slight, decrease in diameter A-B is the area the rings should travel in and never leave. Mine were coming just out side the bevel area. The B-C dimension is what's too long and what I was trying to figure out. But the simple comparison in the picture above shows the problem quite handily even if I don't know the exact dimension.
For those who don't remember here is what a ring looks like if it catches and gets wedge between bolt and bolt carrier.
Ah the joys of DIY, especially when you're buying parts helter-skelter. I'll test the next BCG I get, because I now know what this feels like. But then it'll be something else. The glass is neither half-full nor half-empty in my world. It's just twice as big as it needs to be. Unless it's a wine glass, then it can never be too big.
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