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Posted: 7/8/2012 4:42:58 PM EDT
[#1]
"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. |
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Posted: 7/8/2012 7:04:28 PM EDT
[#2]
I would guess under-gassed.
Are there case/brass markings on your deflector? |
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Posted: 7/8/2012 7:44:20 PM EDT
[#3]
Excuse my stupidity please, but does case markings on the deflector indicate an under gassed condition?
Shannon |
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Posted: 7/8/2012 8:01:43 PM EDT
[#4]
Quoted:
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. |
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Posted: 7/8/2012 8:38:45 PM EDT
[#5]
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.
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Posted: 7/9/2012 7:36:58 AM EDT
[#6]
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.
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Posted: 7/9/2012 7:39:32 AM EDT
[#7]
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.
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Posted: 7/9/2012 8:02:05 AM EDT
[#8]
Chamber cleaned with a Chamber brush/CLP to get out all the storage grease before it was shot?
Your not using Hoppes solvent to clean the barrel right? it leaves behind a residue that collets with the powder fouling to cause problems very quickly. As for lube, hoppes gun oil is not the right stuff either, and should be using CLP. Upper bearing surfaces lubed on the wetter side with CLP for break in? When pulling back on the ejection handle, the face of the bolt stops in from on the ejection port around 1/4", and does not retract back past the back edge of the ejection port? Extractor spring is strong, and the ejector is moving freely in the bolt face channel, just under a great deal of spring tension? Ammo being used for break in is not steel case coated ammo, but brass case factory ammo instead? |
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Posted: 7/9/2012 8:28:24 AM EDT
[#9]
Which buffer?
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Posted: 7/9/2012 9:57:24 AM EDT
[#10]
standard carbine buffer
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Posted: 7/9/2012 11:35:43 AM EDT
[#11]
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.
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Posted: 7/13/2012 2:48:53 PM EDT
[#12]
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. |
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Posted: 7/13/2012 3:21:51 PM EDT
[#13]
N/M
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Posted: 7/13/2012 3:26:35 PM EDT
[#14]
STOP!
Before you go changing parts willy-nilly we need to know what ammo were you using. Also knowing who made the barrel and its port size would be helpful. |
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Posted: 7/14/2012 6:22:54 PM EDT
[#15]
Barrel is DD CHF 5.56mm with .625 gas port
Using 223 remington 55gr ammo |
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Posted: 7/15/2012 2:29:24 PM EDT
[#16]
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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