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308 vs 223 builds

Belt Fed

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I am no gun expert by any means and i have never built one, with that being said i have had a few of mine completely apart and put back together with no problems. but all mine are same manufactured upper and lowers. factory guns.

My question is why are the large frame 10's so much harder getting to function than their small frame counterparts? Is it cause there are a couple designs of 308's that don't match with different uppers or is it way different specs on parts?

I still hear of 223 builds that don't work but nothing like the larger framed guns. Now i'm just talkin build guns not the factory ones.  I know here i have seen numerous threads started on having trouble with the 10 and OP says they have built 223's before with no problem. Is all 15 parts compatible with each other?

Just thinkin out loud here. I have read all the advice and threads on correcting them and have a good idea why they don't work as well, but do the 223's have these same problems. i hear PSA in 223 works fine but their 308's don't without  knowledge on what parts to buy.

I have had only one 308 that wouldn't work right and i still have it and just never done nothing with it to make it work. But i see an awful lot of 308 builds that don't function for some reason and wondered if it's just mainly being educated on the platform and what parts that make it work.

Edited by Belt Fed
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Because there is no mil spec to follow. AR15’s are well detailed out and everyone uses the same specs. Not so on the large frame. Then you get companies changing things around. Save weight and money on the buffer, try to correct that with a smaller gas port. Have different thicknesses for pins and portions of the receivers. Different cuts. That’s why pairing receivers with the same manufacturer is crucial to a good start. Some may work together, but you know they should work together from the same place. And if they don’t, you have one call to make. Not to mention brand A can’t blame brand B while B blames A. 

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The 15 follows a military spec. Those specs require the parts to be manufactured to a blueprinted set of measurements to ensure compatibility. The 10 does not have that spec to follow, hence every manufacturer goes with what they feel is best. Generally there a 3 patterns.

 AR10 (Armalite- the only thing that can be called an AR10, patented and proprietary). 

DPMS/ SR25/LR 308- mostly interchangeable (somewhat, no guarantee because of small machining tolerances, because there is no mil spec) Knights Armament is the SR-25. The make the m110 military rifle used and DPMS patterned their rifles off of this. Many others use a version of this.


Rock River- the RRA pattern was off the original (way long ago) Bushmaster pattern prior to bushmaster being bought by the Remington group. Also a proprietary pattern

Hope this explains it

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Good information above about the three different patterns. 

I built most of my 308-AR's before becoming a member here, and those experiences are well embedded in what's left of my memory banks (Bourbon drinker here) plus a decent size box with several bags of leftover parts in it.

AR-15's are easy as mentioned, and for the most part everything fits across the board.  I hesitate to use the words "Mil-Spec" because many parts follow the Mil-Specs for "size" or fit, but often do NOT meet the entire Mil-Spec requirements as far as material(s), hardness, coating(s), accuracy, etc.

Barrels come to mind first when I say that.  Even so most barrels are decent as far as fit/finish/function, M4 feed ramps seem to be the standard as well,  most will not be chrome lined with full exterior coating per the Mil-Spec and many will have 1-8 or 1-9 twist instead of 1-7......Cliff


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