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I build my .308 semi auto (AR 10 style) rifle. I was having a problem with a round feeding from the magazine because I believe the bolt was cycling too fast. So I either needed a new magazine with a stiffer spring or (what I did) what trim some of the magazine housing back where the rounds are stripped so the round is stripped off sooner. That fixed my problem 100%. However, now I am having a problem where sometimes (not all the time) when I have multiple rounds loaded in the magazine the rifle wont’ fully chamber and lock (pull the trigger and I get a click). Then I need to pull extremely hard on the charging handle to extract the round. However, when I just load 1 round in the magazine it chambers and locks perfect 100% of the time (even using the ammo that previously would not fully chamber and lock when multiple rounds loaded). So this makes me believe that it is not the rifle but still the magazine or perhaps the ammunition. Since I reload my own ammo and bumped the shoulder back about 0.002” could it be that I need to take the shoulder back further, like to SAMMI minimum (usually around 0.005”). Or could it be something with the magazine again since it works with 1 round loaded but won’t with more the 1 loaded (tried with 2, 3,4,5,6 rounds loaded)? It would make since it is the magazine but am not sure. Sorry for the long post but would appreciated some advice? Thanks.
 

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This is exactly the reason why I never try to build lager frame AR. There's just too many variables to go wrong and you won't even know exactly why. That's kinda funny isn't it? With AR15, it's a breeze, like a lego. Fits and works at the first like it's supposed to. But then you get that little larger, all kinds of problems.

With my limited knowledge, it sounds little bit like the timing problem. Gas may be exiting little too earlier or so.

Why don't you show it to your smith and get an opinion.
 

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I would check the head space FIRST.
I've seen this happen with large rounds NOT chambering correctly, and found the head spacing TOO tight.
 

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The issue with the bolt not going fully forward, then being hard to pull the BCG back is most likely because of the way you are sizing your brass. Sounds like the brass isn't sized enough and is getting stuck in the chamber. I would forget about shoulder bumping with an AR, just full length size so it's reliable. Might even need a small base die depending on how tight your chamber is. Brass cycling in ARs does more damage to the brass than full length sizing does in my experience.

Your other issue with it not stripping a round from the magazine could be a number of things. It could be the magazine. Definitely make sure you are using the correct buffer. Large frame ARs use a shorter buffer. If you're using ar15 buffer, it won't allow the bcg to travel far enough to the rear. The bcg would then start traveling forward before the magazine spring has time to push up another round.

Hope this helps.
 

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I totally feel your pain. I’ve got the same situation on a duty rifle. I’m no “expert” so if someone qualified has a better solution, please chime in.

I’ve seen almost everything with my AR-10. Popped primers, double feeds, failure to feeds, failure to chamber fully, fail to eject, fail to extract....

1st, I’d start with a QUALITY, adjustable gas block. Mine is seized up so I’ve had to go other routes.

2nd, look at buffer weights. I’ve tried 3 weights trying to prevent primers from popping hoping to create more dwell time for the pressure to drop. I’m running a short barrel and suppressor so pressures are high.

3rd, you could try a heavier spring pushing the bolt into battery with more force. I’ve tried that as well. But then again, it could create short stroking.

The last thing I would do is modify magazines. Try a different brand/type if nothing else.

Like I said, I’m no expert so if no one else chimes in with good info, it will give you a place to start.

Good luck.
 

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By The Numbers:
1) Upper & Lower Receiver
2) BCG
3) Stock
4) Buffer, Tube, and Spring
5) Magazine Brand(s)
6) LRP Kit

When it comes to processed Chicken Products... Parts are Parts.
Large Frame ARs, Not So Much At Friggin' All.
 

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.308

Will the bolt stay back with just one round? If not it is one of 2 things usualy.
Most common things are the need for adjustable gas block, or misaligned ,mine is almost wide open.
What length barrel? Most mistakes are using a carbine buffer setup when you need rifle length.
You need to use a lot of oil when new, and I mean a lot it will not hurt a thing.
I would look at common sense things like this before you go working up new loads. Mine cycles fine with Hornady match, reloads and 147 grain Winchester so I really doubt it is your ammo.
I just fixed a friends 350 legend and it was lack of oil and a junk magazine that would let the next round pop up just moving the bolt carrier back and would stovepie the round. New magpul mag and oil and it don't miss a beat now.
They are a pain sometimes but most of the time it is something simple and people get mad and overlook the common sense things.
 
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