AR Upper Not Fitting Lower

[tomtom7]

Hi everyone,

I recently purchased an Adam Arms upper and tried putting it on my lower which is American Tactical I believe (I will check and update later tomorrow). I tried attaching the upper to the lower but the rear pin by the fire selector just doesn't want to go in. I took a closer look at it and the upper just needs a little filing and looks like it would fit up.

My question is has anyone else had a problem fitting a upper to a lower? Is it common?

And should I try filing the parts a little to make it fit or maybe buy a new lower?

Any help would be great. Thanks.

[miwxq]

do you have another lower you can try on? like from a friend?

[m16]

I've had this issue with a few of my rifles.

I posted some pics in this thread:

http://www.calguns.net/calgunforum/showthread.php?t=831089

[mindwreck]

American tactical as in their polymer lower?

[SemperFi1775]

Hi everyone,

I recently purchased an Adam Arms upper and tried putting it on my lower which is American Tactical I believe (I will check and update later tomorrow). I tried attaching the upper to the lower but the rear pin by the fire selector just doesn't want to go in. I took a closer look at it and the upper just needs a little filing and looks like it would fit up.

My question is has anyone else had a problem fitting a upper to a lower? Is it common?

And should I try filing the parts a little to make it fit or maybe buy a new lower?

Any help would be great. Thanks.

just make sure the rear take down pin is not in the way of the upper, then slap the upper a bit harder into the lower.

most polymer lowers have a tight fit.

[tomtom7]

This one isn't polymer, it is the usual aluminum. I will try some of what you guys mentioned above and let you know how it works and also post some pictures soon.

[mod1217]

I had the same problem with Adam Arms not fitting lower. A few months back I bought one and its funny it would fit my Spike lower but not my TM lower, I could not get that rear pin to close. What I did is I file the lower takedown pin and pin hole a little, just enough to make it fit but not enough to render the pin that hold the takedown pin useless.

When not attach the takedown pin moves around a bit but when the Upper is attach its a snug fit. I would strongly suggest against filling the upper for AA uppers cost 4 to 5 times more than the lower and AA upper went bought as an assembly is design primary for it's piston system. A new stripped upper wont work cause the hole for the piston is so much more smaller than the hole for the gas block on most upper. So either just return the upper or file the lower

[Palmaris]

I have AA upper and initially it didn't fit into dedicated lower, but did fit in another. After couple of trials I found that outer corners of rear lug was in the way. I just cut those corners lightly and no more problem. Recently my friend got the same upper and it was the same problem, solution was the same. I measured lug and both uppers have the same out of spec +.005" dimension on width of lug, no biggy! Ones corners trimed-everything works fine.
BTW, best upper I ever have-very accurate and never got dirty.

[G21Shooter]

I would try your upper on another lower before you start modifying anything. A friend maybe even a local Calgunner could help you out.

Adams arms is known quality, so I am betting its a out of spec lower.

[gun toting monkeyboy]

It happens sometimes. If you can try it on another lower, I would. If it fits on that, your lower may be a bit tight. If it doesn't fit on another one, it is most likely the lug on the upper. I had that happen, and all I did was sand/file it down a bit, and it eventually fit. It works just fine now.

-Mb

[tomtom7]

Thanks everyone for the continuing input. I will try it on a friends lower over the weekend and give an update if it is the lower or the lug on the upper. Glad to hear people like their AA uppers. It is my first gas piston one and excited to try it out just sucks I ran into this issue.

[m16]

Why bother?

What are you going to do, trade lowers with your friend if it works?

Make the upper work with YOUR lower.

It takes three or four swipes of a file on each corner to make it fit, look at the thread I posted and you'll see exactly what I am talking about.

You aren't altering the upper in a way that will make it unusable with other lowers, make it fit and forget about it.

[Aznatama]

I have 2 different uppers, one fits in my billet lower, the other one doesn't.

The one that fit is a PSA complete upper, the one that didn't fit was a cerro forge upper. It seems like it's the rear edge that's a little bit too "high," and required a little filing. No big deal.

The only think I'd be concerned with is filing away the hard annodizing on the upper/lower. I would NOT modify the pin itself, since that would make other uppers fit loose.

[peter95]

One of my PSA lowers had a very tight fitment with my upper also.

I had to file down part of my upper receiver to fit it with a dremel.

Then I also had to dremel some of the rear take down pin since it was pretty much stuck and impossible to pull it out without having to bang it out with a tool.

[tomtom7]

I looked over you post M16 and will try out and look at the parts you mentioned tomorrow and see how that looks.