View Full Version : AR lower / upper receiver question

07-27-2007, 2:04 AM
An academic question. As most of us are matching uppers and lowers from different manufacturers, is it possible that the two parts are not always a perfect fit? Are some manufacturers worse than others for fit?

What is considered an exceptable (if any) gap in the fitting in between the upper and lower receiver on an AR? What is the mil-spec on this? In other words, is it bad news to be able to see daylight between the upper and lower?

And if it exceeds the allowable gap, would this cause feeding problems?

07-27-2007, 1:51 PM
Mil spec is mil spec. I am sure there are poor quality uppers/lowers and I would say that my main concern is if the take down pin holes match.
You may also look at "Bwiese" post here

07-27-2007, 1:54 PM
I was more worried about the different finishes different companies use....Some arent even close to matching and look kind of two toned.....I ended up going with a full CMMG setup

07-27-2007, 2:32 PM
Well if you can get the pins to go through the upper....you shouldn't have any issues.....:chris:

Daylight bwtn upper and lower isn't a general cause for alarm....mostly aesthetics......just like the finish...;)

If you have trouble w/ the rifle, than you can look at out of spec pieces.

07-27-2007, 8:50 PM
I've heard that most true mil-spec rifles, ie M16s are loose and rattle when you shake them. That said, several companies that build match rifles will fit the upper and lower so there is no play. I like to use Stag or High Standard lowers because they seem to lock up tighter than a lot of other brands. They also have some of the best machining and lowest prices, which is an added plus.

07-27-2007, 11:27 PM
I have a Stag upper and an RRA lower that fit together like they were milled from the same billet. No daylight anywhere.

I also have a Bushmaster that I bought as a complete rifle, and there's a slight crack of daylight between the upper and the lower. Has zero impact on function in my experience.