Quick question...upper swap

[Lyptix]

I just got a Rock River complete lower from a fellow glocktalker...when I got home, I got out my bushy complete rifle. I took the upper off of my bushmaster lower and put the bushmaster upper on the rock river lower. It seemed very tight to get it to set down. The guy I got it from said he never had an upper on it. Looks very new. Mean while my bushy I got is used and has had a lot of rounds put though since I have had it...is it just tigh becuase its a newer lower and needs rounds though it to feel loose? or is something else wrong? My bushmaster pins can be pushed out and taken apart very easily. any ideas or input?

[Critter]

Normal for a RRA lower. There are two machining steps that are omitted on the rear inside of the RRA/Stag/CMT's that give those lowers a tighter fit. It's not excatly a bad thing until some tolerance stacking goes on which is what you may be experiencing. It will not hurt anything though and will break in with use.

Let me guess about your Bushy, the serial number begins with an 'L', right? If so, great lower receiver, all is good. That particular manufacturer of those receivers does a great job, I prefer them, use them directly from the manufacturer under their name, not Bushy, but still the same receiver. The cosmetics on the outside area are little rougher, but not noticeable enough to me to worry about it, even though they are a little more expensive. All is good, don't sweat it.

[GixxerSixxer]

My RRA lower with a Del-Ton upper was very tight at first. I had use use a hammer to get them in.

Now after 200 rounds I can use my fingers to push in/out the pins.

[Critter]

It's the back rear corners of the upper that are rubbing. This area is narrow on the RRA lowers. If the tolerances get stacked too much you have to releive the areas on the upper in some cases.