Question on AR15

[RickyT]

I was kinda under the impression that AR15 parts were interchangeable. The reason I'm asking was a friend wanted to trade me his DPMS upper for my Bushmaster. Mine was is just the 16in A1. His was a 20in flat top. The uppers would not fit on each other. On the Bushy I pushed the front pin in and lowered the back of it and the tab would not line up with the pin, the tab hole was almost a 1/4 in forward and the pin would not go in. Also the contours on the back of the upper didn't appear that they would be a flush fit. So no trade. Was this a rare situation? Cheap models?

 

[charliepapa]

I never heard of that either unless one was a 308 (AR-10)

 

[whbonney26]

Never had that problem either. Some fit a little tighter than others and I have ran across some poorly machined pins that made it more difficult to get through but never had them not work.

 

[RickyT]

They were both 223. I could have drilled the tab that the pin goes through but it would have made it thinner on the front half.

 

[scooterj]

Is the Bushy a Carbon-15?

 

[CloudStrife]

They were both 223. I could have drilled the tab that the pin goes through but it would have made it thinner on the front half.

I've read that some AR parts aren't hardened all the way through, so I wouldn't go drilling on the receiver.

 

[Richard in LA]

I was kinda under the impression that AR15 parts were interchangeable. The reason I'm asking was a friend wanted to trade me his DPMS upper for my Bushmaster. Mine was is just the 16in A1. His was a 20in flat top. The uppers would not fit on each other. On the Bushy I pushed the front pin in and lowered the back of it and the tab would not line up with the pin, the tab hole was almost a 1/4 in forward and the pin would not go in. Also the contours on the back of the upper didn't appear that they would be a flush fit. So no trade. Was this a rare situation? Cheap models?

Both are factory rifles? seems kind of odd, as an above poster mentioned sometimes they are snugger fit, but never off by that much. One of them appears to be out of spec by a large margin, but which one is it? Possibly you could find another known quality, In-spec upper from someone for a test and see which rifle it fits and which has problems to narrow it down. The gap that may or may not be present should not affect function/accuracy of the rifle, but may bother people concerned with cosmetic appearance.

I've read that some AR parts aren't hardened all the way through, so I wouldn't go drilling on the receiver.

The aluminum recievers are anodized, which is just a surface hardnening process. I wouldnt think that a small amount of reaming on the takedown pin hole would hurt much, as it is not a rotating/moving part, but 1/4" is a bit much to be messing with.

 

[RickyT]

Is the Bushy a Carbon-15?

No it's not carbon. Both are factory set ups. I'm going to try and get a 3rd one involved and see if we can figure out which one is out of spec. I was hoping to get that upper in the the trade but it won't happen now.

 

[scooterj]

That's really strange. I've got Bushy, DPMS, S&W, and Esential Arms lowers and all 4 uppers will fit all 4 lowers.