STI AR15 uppers

chemo

chemo

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Recently bought a stripped one and they are rifle uppers (ie without the m4 cut). I had bluntly assumed uppers were all m4 cut nowadays, my mistake. Anyway it shouldn't be a problem with the barrel I will be using so this not actually a complaint

Not looking to start a heated debate over m4 upper and barrel cuts vs rifle cuts and mix and matching, but just passing this on FYI


edit: pics of the actual upper. It was purchased stripped, I had the rest on hand. These uppers are very nice. Looks cleaner than the DD I have.

 
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I bought an NEA upper and I was pleased they were making them without the M4 cuts as I wanted to use my existing barrel. Seemed like the majority of bare uppers are m4 cut when I was looking.
 
civicbam said:
What's an M4 cut? Trying to learn and have been looking the the STI stuff.
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They are feed ramp cuts that start in the receiver and continue into the matching deeper cuts in the barrel.

Non- M4 or standard rifle receivers have no cuts in the receiver, and the feed ramp is purely cut into the barrel.

Apparently the M4 design is to aid feed on full auto.

If you stick a non-m4 barrel on an m4 receiver, you get a mismatch where they meet up but don't blend into each others ramps it could cause problems.
 
feedramps2.jpg
 
Yeah...I don't think they have any receiver cuts, if they do, they are surely shallow.

However, I'm not sure all competition rifles come with them as a standard, they aren't really required for semi's from what I understand.
 
Onagoth said:
Yeah...I don't think they have any receiver cuts, if they do, they are surely shallow.

However, I'm not sure all competition rifles come with them as a standard, they aren't really required for semi's from what I understand.
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yeah, I have updated the original post to show the lack of cuts.

Your comment seems to imply you have one or have been shooting one?
After checking, from what I have seen over on ar15.com, their actual rifles are shipped with m4 extension cuts into a non m4 upper.

I don't understand why the AR15barrels.com picture says it is just an "OK" situation. From a mecanical point of view, I would be inclined to think it is less prone to binding than m4 upper/m4 barrel-combo since the bullet does not encounter a "seam" in in the rifle receiver/m4 barrel-combo. But I'm just thinking out loud.
 
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