well....
Finally went to the range today to try the gun with these buffers from Brownells. Standard weight, one is from Brownells and the other from Rock River, both are excellent quality
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First I did the single round in a magazine, shoot it, to see if the bolt catch worked, locking the bolt carrier back. It did. Tried another magazine, it did as well. This looked promising!
Then I went to test a full 20 round magazine. I truly expected this to resolve the issue but it didn't. I could only get about 6-7 rounds off before getting a jam like this
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Now I'm bummed. Gun turned from an ultra reliable firearm to a Jam-O-Matic.
A little backstory. I bought Colt LE6920 when the ban first expired. Even though it didn't have the sear block like the Colt Sporter Lightweight did, it did come with a cut out bolt carrier.
A year or so ago the 6920 was misbehaving and I thought it was the extractor or something. Thought it would be a good idea to get a new BCG, so I bought the Colt AR15/M16 group, slapped it in the 6920 and it worked fine ever since. Had the side affect of giving me a spare cut out bolt carrier for the Sporter Lightweight as well, as the 6920 doesn't require the cut out carrier even though it came from the factory that way
Then I read up on troubleshooting and that cut out bolt carrier, the one on the bottom, had worn gas rings:
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I did the test where you extend the bolt, stand the BCG on a table and see if the bolt pushed in. It did. So I replaced the gas rings on the bolt for that bolt carrier
I did the same test for the bolt carrier from the Sporter Lightweight, as you can see it passed:
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Ends up looks are deceiving and I was deceived. Even though it passed the test, a light touch would make the bolt push in. On the LE6920 carrier, more effort was needed.
On a whim I swapped the Sporter's BCG with the LE6920's BCG that had the new rings and test fired the Sporter
No jams!
This was with one of the new standard weight buffers.
I put the Colt H2 buffer in the Sporter and test fired again. No jams!
Decided to do one more test, 3 x 30 rd mags and 1 x 20 rd mags.
Bam bam bam bam ...bam bam....bam!
No jams, no failures. Running like a champ, this was with my high quality reloads as well.
So in conclusion, the standing the bolt carrier on a table test gave me a false positive. Going to put new rings in the Sporter's original bolt and test it next range trip.
Gloated all the way back from the range.