How common is it for an upper not to fit a lower?

[WS6]

Is this normal? Will a company replace the upper?

[SpankMonkey]

Its not normally common, but it does happen. Most companies will replace it if you call them.

Make sure it is not the lower first.

[WS6]

Its not normally common, but it does happen. Most companies will replace it if you call them.

Make sure it is not the lower first.

It can't be the lower, it's a registered SBR lower.

[Failure2Stop]

It can't be the lower, it's a registered SBR lower.

Did you check the compatibility of the lower with known-quality uppers?

[WS6]

Did you check the compatibility of the lower with known-quality uppers?

It fits very tight on a PSA upper and a VLTOR VIS/MUR upper.

[serbonze]

It happened to me. The upper receiver was out of spec. I sent it back to the manufacturer, they replaced the upper and returned it to me.

[WS6]

It happened to me. The upper receiver was out of spec. I sent it back to the manufacturer, they replaced the upper and returned it to me.

Upper is measuring 0.498, lower is 0.497. I got it together once, thinking it would wear in, but the rear pin wouldn't go through and I had to tap them apart. I'm calling the manufacturer of the upper in the morning, and have already e-mailed them.

[jonconsiglio]

I've see this happen with RRA lowers a couple times. When I got my 9" AAC upper a couple weeks ago, it didn't fit on my Noveske lower. I had to use a rubber mallet to get the takedown pin through. After that and a couple times by hand it fit like any other upper. I'm assuming it was the anodizing or something like that.

[Tzook]

Upper is measuring 0.498, lower is 0.497. I got it together once, thinking it would wear in, but the rear pin wouldn't go through and I had to tap them apart. I'm calling the manufacturer of the upper in the morning, and have already e-mailed them.

My friend bought a factory Bushmaster that was insanely tight just like that, he says it's loosened up a fair amount over time.

[AKDoug]

Your lower is right on the bottom edge of the spec. The lower receiver blueprints call for .500" +0.000/-.004 It is likely that it will be problematic with many uppers. I've yet to find a blueprint for uppers so I can figure out what their specs are. (ETA: I have found upper prints, but none of them have the dimension for the mating surfaces between the upper and lower) I would imagine that there is some point within the tolerances that a upper on the big side of spec won't fit in a lower that is on the small side of spec.