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Posted: 2/14/2016 2:10:35 PM EDT
So I finally took my first build out to the range. It is a bcm 14.5 mid length. When shooting IMI 193 the bolt would not always lock back on the last round. I would say 75 percent of the time it did not. I then used IMI 62 grain and it did seem to start locking back more frequently. I will test again when I get more ammo. I am just wondering if it is short strocking or why it isnt locking back all the time. I was using 30rnd pmags, H buffer and a tubbs flatwire spring. Would switching springs back to a standard carbine spring help? Lighter or heavier buffer?

Link Posted: 2/14/2016 2:44:38 PM EDT
[Last Edit: 2/14/2016 2:45:51 PM EDT by Tomac]
BCM 14.5" middies come w/the warning that they're designed for full-power ammo only so short-stroking is a real possibility. Clean, lube, std carbine buffer and buffer spring, retest.
Tomac
Link Posted: 2/14/2016 2:52:32 PM EDT
[Last Edit: 2/14/2016 2:53:50 PM EDT by Bushy24]
I'm certainly not an AR specialist, but from my limited knowledge there's not enough umphh to get the bolt back all the way. A few things could help this...
Regular weight buffer
Lighter bolt carrier group
Maybe a slicker BCG, or better/more lube
More gas to the receiver, adjust your gas block if it's adjustable
More get up and go with your ammo.
The easiest and for sure way would be to have a higher charged round.
Link Posted: 2/14/2016 2:54:25 PM EDT
What is considered full power ammo?

I think I may have found the problem. One of my pmags. When inserting the empty magazine it does not actuate the bolt catch/release. When pulling the bolt back and releasing slowly it gets caught on the magazine follower and not the bolt catch Then when dropping the magazine, the bolt will release as it was being caught on the magazine. I tested the other pmags, and when inserting they actuate the the bolt catch and the bolt locks all the way the back and not on the magazine. Hmmm...faulty pmag?

This would explain why somewtimes it would lock back and not, I only brought 2 magazines one of them being this, I think, faulty one.
Link Posted: 2/14/2016 3:24:58 PM EDT
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Sliver1357:
What is considered full power ammo?

I think I may have found the problem. One of my pmags. When inserting the empty magazine it does not actuate the bolt catch/release. When pulling the bolt back and releasing slowly it gets caught on the magazine follower and not the bolt catch Then when dropping the magazine, the bolt will release as it was being caught on the magazine. I tested the other pmags, and when inserting they actuate the the bolt catch and the bolt locks all the way the back and not on the magazine. Hmmm...faulty pmag?

This would explain why somewtimes it would lock back and not, I only brought 2 magazines one of them being this, I think, faulty one.
View Quote


Full power ammo would be 5.56 ammo vice .223 ammo (although Wolf Gold .223 is very nearly 5.56 power-wise and PMC Bronze .223 is weak, even for .223).
Retest w/good ammo, carbine spring/buffer and different mags. If that solves your problem you can retest using the heavier buffer & spring.
HTH...
Tomac
Link Posted: 2/14/2016 6:39:18 PM EDT
Clean it, Lube the carrier's rails, as well as the hammer and trigger pins with gun oil.
A light coating of gun grease on the hammers top cocking flat.

And get rid of the H3 and get a standard carbine buffer.

If it still wont lock back on last round, Springco makes a reduced rate buffer spring.
Link Posted: 2/14/2016 7:35:11 PM EDT
Thanks for responses everyone. After seeing what was happening with the magazine I think this might be the issue. It was the primary mag I was using at the range. It this typical with pmags?
Link Posted: 2/14/2016 8:02:39 PM EDT
What kind of gas block are you using?
Link Posted: 2/14/2016 11:46:02 PM EDT

Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Sliver1357:


Thanks for responses everyone. After seeing what was happening with the magazine I think this might be the issue. It was the primary mag I was using at the range. It this typical with pmags?
View Quote




 
No, that is not typical with pmags. I would contact them about replacing it. You must be chomping at the bit to get back on the line without that bad mag and see what happens, so be sure to let us know how it works out.




Oh, and welcome to the community.
Link Posted: 2/15/2016 12:08:34 AM EDT
Im not really sure on what gas block it is. I bought a complete mid length upperick from bcm. And thank you for the welcome. I will contact magpul and see what they say. But yes, I can't wait to get back out. Wednesday i will be going and only use the good mags and see what happens.
Link Posted: 2/15/2016 8:42:30 AM EDT
[Last Edit: 2/15/2016 8:48:54 AM EDT by RogueSpear2023]
I would try a different magazine but really your going to want to run a standard buffer, and std carbine spring. I have 14.7" midlength and mine will eat anything, but i am using a standard buffer and spring.

Your spring is increasing bolt force by 10% and then you add a H buffer which is .7 oz heavier than standard in a upper that is going to be under gassed to some degree even if built properly. Those two things are most likely going to be your problem.
Link Posted: 2/15/2016 8:06:22 PM EDT
I'd think that if it was under powered ammo or spring too stiff/buffer too heavy that he would be having all kinds of feeding issues too. Since it's just a lock back issue and you noticed a mag not actuating the bolt lock I'd guess it's a mag problem. But still I would swap out for a standard carbine buffer and spring anyway.
Link Posted: 2/21/2016 9:39:04 PM EDT
Finally got it back on the range. I removed the tubbs spring and put the carbine spring in. I left the H buffer as I do not have a standard carbine buffer spring. Anyways, picked up a couple more magazines and did not bring the one that was under suspicion of not locking the bolt back. I had 200 flawless rounds. The bolt locked back everytime. I will contact magpul and see if they wont send a replacement or new follower. Thanks for the help guys.
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