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Posted: 12/30/2014 11:11:22 AM EDT
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I have a home build AR that is a Rifle gas 17" barrel(gas port enlarged) with a carbine spring and 3.0 oz buffer. Mags are D&H with magpul followers. (They run fine in my PSA mid length with 3oz buffer and 16" mid gassed barrel.)
Any idea why it FTF's? The bolt is stuck on the back of the case with the nose stopped on the feed ramp. Sometimes it bolt over base FTF's also. Ejection pattern is about 3:00, I think. Any ideas? New spring? New buffer weight? New mags? |
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Quoted:
Any idea why it FTF's? The bolt is stuck on the back of the case with the nose stopped on the feed ramp. Sometimes it bolt over base FTF's also. Ejection pattern is about 3:00, I think. A failure to feed like you describe can be bad presentment angle (from mag catch not screwed in enough), or rough feed ramps (that will break in eventually), or a weak spring, or bolt carrier binding, or some combination of any of those. Check that the mag catch is screwed in until the bolt face is flush with the button, feel the feed ramps for burrs and sharp flashing, make sure the bare bolt carrier moves freely in the upper and doesn't bind on the gas tube or elsewhere. My bet's on rough feedramps and/or mag catch not screwed in all the way. |
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Sounds like a burr on the feed ramps. Best cure for that is to drill a 1/8" hole in the end of a 5/16 hardwood dowel about 12" long, then epoxy a 1/4" diamond Dremel bit into the hole. Use the dowel as a handle to work the Dremel bit up and down the feed ramps, and you will quickly find any burrs.
Properly deburred, you will be able to insert the tool in the hole in the back of the receiver, and slide the tip of the 1/4" Dremel bit up the feed ramps past the locking lugs without snagging on anything. |
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A bit more info...
10 13/16" free .072" wire 38 turns 3 oz buffer Does this look right for the spring? It is the same as my newer Mid length. I'll compare feed ramps at the next break.... Trying to decide if I should order P mags as a possible improvement. Might clean BCG too and eliminate grease. BTW, gun ran pretty good on Orlite mags...like never had an issue, except with steel case ammo, but would like to run that too some day. |
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Looked at the feed ramps. They are smooth, but not flush to minus with the M4 ramps on the receiver, but I don't think that comes into play. I say that because the bullet tip hits the feed ramp way above the receiver feed ramp. .... Remember, this rifle fed this load in load development, but from my friends 20 rd mags...I also changed the scope, but that can't affect it, right?
Cleaned the bolt and eliminated all grease....now only Weapon Shield graces the BCG. |
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~ 50 rounds downrange today and NO issues. Is it possible that removing grease and replacing with weapon shield fixed it? Weather was the same...low 30's....hmmm.. GREASE? Yes - don't use grease on any part of the AR. It slows down the carrier and is out of spec for the weapon. Use CLP. |
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