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Discussion Starter #1
Ive had this AR for about a year and so far have had nothing but problems with it. :banghead From what I understand the lower is a beautiful and expensive pre-ban piece of machinery... the upper I have no idea WTF it is. I bought it used just to avoid the WTF did you do to it flaming... from what ive been able to find out is it has all colt internals in the bolt carrier aside from the gas rings I recently replaced (first problem: short stroking).

Now for the main issue. I've been having issues with double feeds when both firing and cycling the bolt carrier. Ive tried different mags from the garbage 5 dollar stamped on up to the 50 to 60 dollar holy WTF mags. SAME ISSUE. When the bolt comes back to cycle a new round into the chamber the bolt carrier knocks a round into the breech and when the carrier comes back forward it does what its supposed to do which is load a round... however, we now have 2 rounds in the breech. when inserting a fully loaded 20 or 30rnd mag it seats with difficulty or just plain refuses to seat unless the breach is open.

one other thing, the top round in the mag is pushed down on by the bolt carrier when the mag is seated.

Ive stumped my local gunsmith but I was wondering if anyone else had a similar experience.
 

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I can only guess differences in the upper and lower. Maybe the lower has slightly different specs in relation to when the mag seats. And the mag sits a bit to high in the lower for the upper to cycle properly.
 

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You said "When the bolt comes back to cycle a new round into the chamber the bolt carrier knocks a round into the breech". If I understand you correctly, the bolt carrier is somehow knocking a round out of mag when the charging handle is pulled back? :wtf

Do you have a friend's upper that is known to work that you can slap on your lower to rule out problems with the lower being out of spec? If that doesn't fix it, it's likely (but not guaranteed) a problem with the lower. If it does work, try swapping out just your friend's bcg with your's.
 

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I can only guess differences in the upper and lower. Maybe the lower has slightly different specs in relation to when the mag seats. And the mag sits a bit to high in the lower for the upper to cycle properly.
This.

If the carrier is stripping rounds of the top, the mag is seated too deep.

Do what beanfield suggested.
 

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I'm agreeing with beanfield as well. I won't rule out the possibility of an out of spec lower but I would look at the mag catch first. That's if you can swap lowers and still have the same issues.
 

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When the bolt comes back to cycle a new round into the chamber the bolt carrier knocks a round into the breech and when the carrier comes back forward it does what its supposed to do which is load a round... however, we now have 2 rounds in the breech.
so am I understanding your getting two "new" un-struck rounds in the chamber when the carrier comes forward, or do you have one spent case in the chamber and one new round piggy backed behind or wedged under the spent case?

if your issue is two "new" rounds, then I think Bean maybe nail-on. Ive heard, not see it myself, where the lower will position the mag in such a way that the face of the bolt picks up a new round as it's moving forward into battery, AND the bottom of the front shoulder of the carrier will also strip off a round and cause a dbl feed.

I'm assuming the Lower is a Colt, is that correct? do you know if it's a .170 or a .1555 pin (Trigger\hammer) lower?
 

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Discussion Starter #10
Ok so I FINALLY figured it out! I got a hair across my ass and decided to take it down to the local gunsmith to swap out for a flat top upper, since we reused my old barrel, the feed ramps had to be cut deeper in the barrel extension and now it cycles like a dream! oh and I took a closer look at the BC and found that it had been ground down right under the back of the firing pin. Our best idea isthat the previous owner thought that modding the BCG would make it full auto:facepalm. so I ordered a new DPMS BCG, some Pmags, and just had a DPMS flat top upper installed. I do believe im good to go!

Thanks for the advice! :cheers
 

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Actually the AR15's bolt carriers are ground down at the firing pin. This is so the hammer will catch on the firing pin. If it is not ground down, it wil be an M16 bolt carrier & not in compliance. Glad you figured the rest out though.

Here is some reference material for you http://www.ar15.com/content/legal/AR15-M16Parts/index.html

Pic shows AR15 on left M16 on right

 

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Discussion Starter #13 (Edited)
Well, the good news is that the original problem us fixed... Now its not ejecting properly, my gunsmith wants me to drop it off with him to just work all the kinks out at the range. It's pissing him off just as much as me. He thinks the buffer spring may be too strong or it could be the bolt. I went ahead and rebuilt the bolt (new extractor, spring, and pin) the gas rings are brand new btw, I just got done cleaning out the gas system too. I know I'm in the home stretch and this is all part of black plastic fever but I'm beginning to lose hope on this build.
 

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Discussion Starter #17
Ok I dropped it, about 80rnds, 3 mags, and all my spare parts for it with my gunsmith. I guess he's gonna go shooting tomorrow. Basically, he's going to swap out parts until the problem is solved... He thinks I may have figured out the ejecting issue when I got bored and rebuilt the bolt. hopefully, it fires like a dream for him.... Im getting tired of dumping money into it and not seeing a result! lol
 
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