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Posted: 7/8/2012 3:44:09 PM EDT
[Last Edit: 7/9/2012 10:29:03 AM EDT by mkoch78]
Just installed a new 14.5 mid-length barrel and having two issues:

1- Casings eject to about 2 o' clock and only eject about 1- 2 feet.
2- Shot about 60 rounds, (1 round in the mag at a time, range rule) and 5 of those 60 the bolt failed to lock back


I've read that casings ejecting at 2 o'clock indicate over- gassed, but the bolt failing to lock back indicates under-gassed?

Which do you think it is??
Link Posted: 7/8/2012 4:42:58 PM EDT
"5 of those 60 the bolt failed to lock back"

Vote for slightly undergassed with that ammunition.
Check your bolt & bolt carrier for gas leaks. Check the gas tube is not dragging on the gas key.

Clean the chamber with a good solvent and then try shooting againi with a diffrent lot of ammo.

Failing to lock back when shooting 1 round from the magazine is a sign of under gassed trouble.


Link Posted: 7/8/2012 7:04:28 PM EDT
I would guess under-gassed.

Are there case/brass markings on your deflector?
Link Posted: 7/8/2012 7:44:20 PM EDT
[Last Edit: 7/8/2012 7:50:58 PM EDT by ShannonD]
Excuse my stupidity please, but does case markings on the deflector indicate an under gassed condition?

Shannon

Link Posted: 7/8/2012 8:01:43 PM EDT
Originally Posted By ShannonD:
Excuse my stupidity please, but does case markings on the deflector indicate an under gassed condition?

Shannon



My question is just a little research on a theory.
Link Posted: 7/8/2012 8:38:45 PM EDT
Yup under-gassed is your issue here. Signs are weak ejections and failing to lock back on empty mag. Check your gas key, make sure it's tight. Check your gas block, make sure its lined up with barrel gas port. Maybe try hotter ammo. Another option would be to get an adjustable gas block.
Link Posted: 7/9/2012 7:36:58 AM EDT
Yes, I noticed new markings on the inside corner of the deflector. I read that this may indicate that the casings are ejecting straight back, hitting the inside corner of the deflector, then going out at 2 o'clock. Trouble is its almost impossible to verify this with the naked eye.
Link Posted: 7/9/2012 7:39:32 AM EDT
Thanks. I just switched from a 16" carbine (that I thought was overgassed) to a 14.5" middy . Are all 14.5" middys undergassed or is it just mine. Checked the gas key and its OK. The gas block is pinned so I don't see how it couldn't be lined up right.
Link Posted: 7/9/2012 8:02:05 AM EDT
Link Posted: 7/9/2012 8:28:24 AM EDT
Which buffer?
Link Posted: 7/9/2012 9:57:24 AM EDT
standard carbine buffer
Link Posted: 7/9/2012 11:35:43 AM EDT
pull upper, flip the upper over and slide the BCG back and forth, it should lock up really smooth and not drag on gas tube. If it drags you can "adjust" it. ie bend the tube ever so slighty with an easy hand. It is easy with the handgard off.
Link Posted: 7/13/2012 2:48:53 PM EDT
Checked gas key and its OK. Checked the movement back and forth over the gas tube and its OK too.

I'm going to try some 5.56mm rounds this weekend to see if this slightly more powerful round will help the undergass issue.

Link Posted: 7/13/2012 3:21:51 PM EDT
[Last Edit: 7/13/2012 3:22:21 PM EDT by DeltaBravo555]
N/M
Link Posted: 7/13/2012 3:26:35 PM EDT
[Last Edit: 7/13/2012 3:28:20 PM EDT by eric10mm]
Link Posted: 7/14/2012 6:22:54 PM EDT
Barrel is DD CHF 5.56mm with .625 gas port
Using 223 remington 55gr ammo
Link Posted: 7/15/2012 2:29:24 PM EDT
ISSUE FIXED!! This whole troubleshooting has been very interesting. Turns out the gun is not over/ undergassed but was ejecting poorly because of a tight chamber and possible the Magpul BAD lever disrupting the function of the bolt catch.

My latest attempt worked by A) polishing the chamber with a cotton mop on a drill with Flitz polish and B) removing the BAD lever I had installed.

Went to the range today fired 20 5.56mm and 20 .223 , both 55 gr. Each shot functioned flawless and locked back on each shot with empty mag. My ejection even improved from very weak ejections of 1-2 feet to ejections of 7-10 feet at 2-3 o'clock.

Conclusion is the new barrel had a really tight chamber that had to be worked in and polished really well.

Thanks all for the help.
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