Help with ugly FTE

[WS6]

How I would approach this, starting from cheapest/easiest/shoulda-already-done, to most expensive, were I to decide to not call BCM first:

-Observe to see if ejection/cycling is "abnormally violent" and if so, correct with H/H2/H3 buffer (as required) and Mil-spec spring. I have fallen in love with my Android phone filming cycling at 240fps, as that is JUUUSTTT slow enough to observe secondary (buffer hitting back of the tube) and tertiary (BCG slamming home) recoil forces and aid me in selecting the optimal buffer/spring (I like sprinco springs, but Mil-spec works and is a known quanity.)
-Use chamber-brush to clean chamber/visually inspect chamber with a good light.
-Manually depress ejector with a case-rim to see if it is impinged or not, and that the spring has good tension.
-Inspect extractor/bolt face for deformity of any kind.
-Replace extractor spring with Colt Gold extractor spring. Get rid of any "doughnuts" or the like.

If this did not fix it, I would throw my hands up and ship it to BCM if they told me to so that they could figure it out.

[t15]

Thanks everyone, I am certain the bolt is slipping off the case and going all the way back as I can feel the buffer bottom out in the tube. I have a BCM extractor upgrade kit laying around somewhere, I will try that first, and then gas rings.

I'll update the thread with results!

edit: forgot to mention 2 of the pictures are of the bolt locking back on empty with a pmag 20 after loading 1 round at a time and failing to extract, this is my major clue that it is not short stroking. Just dug around in the box and found the 3 pack of BCM springs w inserts and another sealed bag with a set of gas rings and the firing pin retainer, should be able to test this for curiosity's sake soon. I did leave an email with BCM.

Thanks again m4carbine.net!

[WS6]

Thanks everyone, I am certain the bolt is slipping off the case and going all the way back as I can feel the buffer bottom out in the tube. I have a BCM extractor upgrade kit laying around somewhere, I will try that first, and then gas rings.

I'll update the thread with results!

I don't see how it's gas rings. However, I am a huge fan of the correct spring vs. bandaids. I recommend the Colt solution.

[t15]

I dunno WS6, I've got them and it's an easy swap so I'll try it! Bolt face and extractor look OK, I put an empty case in there and the ejector seemed normal as well. I've ran a rip cord multiple times and don't see any burs in the bore. I worked into the barrel extension with a Q tip and at the range the bolt was all the way in battery. As far as the Colt gold spring, I bought some 5 coil Sprinco's a while back, so will be running those. For now, my goal is to establish if there is a material problem with the rifle in some way or just an out of spec consumable part like the gas rings as BuffardT suggested. I want to copy whatever setup BCM shipped it with and not band aid the problem with extra extractor tension. Thanks for the help, I'll be hitting the range soon!

[BufordTJustice]

I dunno WS6, I've got them and it's an easy swap so I'll try it! Bolt face and extractor look OK, I put an empty case in there and the ejector seemed normal as well. I've ran a rip cord multiple times and don't see any burs in the bore. I worked into the barrel extension with a Q tip and at the range the bolt was all the way in battery. As far as the Colt gold spring, I bought some 5 coil Sprinco's a while back, so will be running those. For now, my goal is to establish if there is a material problem with the rifle in some way or just an out of spec consumable part like the gas rings as BuffardT suggested. I want to copy whatever setup BCM shipped it with and not band aid the problem with extra extractor tension. Thanks for the help, I'll be hitting the range soon!

That Springco 5 coil is damn near bomb proof. It's all I use now, though one could hardly go wrong with the new copper washed spring from colt.

[t15]

OK, got to the range today and here are the results. Before going, I replaced the gas rings with new BCM ones, no other changes made, no effect on performance-still jamomatic.

Replaced the extractor spring with a new BCM unit and also replaced insert, still jammed. Installed rubber O ring and 60 trouble free rounds!

The BCM BCG that came with the upper had their CS 4 coil? spring installed and no O ring, it was identical to the ones in the multi-pack I had that said you may not even need the O ring on the packaging. I am wondering if anyone else has had to install an extra power spring or use O ring on their short barrel to make it function?

I am going to check the DD and friends BCM bolts from the OP to see if they had O rings or not. If they don't and were running OK without O rings, I guess I will still call BCM?

edit: I am curious if anyone is running an SBR with BCM's enhanced CS spring and insert, but no O ring.

[pingdork]

OK, got to the range today and here are the results. Before going, I replaced the gas rings with new BCM ones, no other changes made, no effect on performance-still jamomatic.

Replaced the extractor spring with a new BCM unit and also replaced insert, still jammed. Installed rubber O ring and 60 trouble free rounds!

The BCM BCG that came with the upper had their CS 4 coil? spring installed and no O ring, it was identical to the ones in the multi-pack I had that said you may not even need the O ring on the packaging. I am wondering if anyone else has had to install an extra power spring or use O ring on their short barrel to make it function?

I am going to check the DD and friends BCM bolts from the OP to see if they had O rings or not. If they don't and were running OK without O rings, I guess I will still call BCM?

edit: I am curious if anyone is running an SBR with BCM's enhanced CS spring and insert, but no O ring.

Not sure what the O ring is you speak of, if you could post a pic I'll let you know if my BCM bcg has it. My bcm 11.5 upper just arrived on friday. Zeroed and function tested appox 200 rounds mix of brass american eagle .223 and 5.56 55grain, 62 grain fmj and green tips, along with 40 rounds of herters steel.

I'm just running a standard spring and H buffer for now, not the softest shooter, but thru first 240 rounds no hiccups.

[Ryno12]

Not sure what the O ring is you speak of, if you could post a pic I'll let you know if my BCM bcg has it. My bcm 11.5 upper just arrived on friday. Zeroed and function tested appox 200 rounds mix of brass american eagle .223 and 5.56 55grain, 62 grain fmj and green tips, along with 40 rounds of herters steel.

I'm just running a standard spring and H buffer for now, not the softest shooter, but thru first 240 rounds no hiccups.

He's referring to the Crane O-ring.

http://www.bravocompanyusa.com/BCM-E...%20upgrade.htm

OP, I've never had to use one in any of my ARs.

[SteveL]

Neither of my BCGs needs the O-ring to function properly. One is a BCM BCG in an 11.5" upper and the other is a DD in a 16" upper.