Gunsmithing Help with Commercial ar lower and Milspec upper

[sch2046]

I have an old Rock river arms lower, had it for years. It won't fit any of my mil spec uppers, the rear pin area is too narrow for the upper to fit, I was going to file a small portion away till the upper fit.

My question is, once I get the upper to fit, will my bolt work in the commercial buffer tube? What pitfalls am I looking at?

 

[Kells81]

Re: Help with Commercial ar lower and Milspec upper

There is no such thing as mil spec and commercial upper/lower... There is. Milspec and commercial buffer tube though. Your problem is you need to put your "man" hands on it to get it together. Sissy hands won't get that pin in there especially with the RRA lowers. As you use it the pin will cooperate a bit more. Don't file anything

 

[chakup]

Re: Help with Commercial ar lower and Milspec upper

The above nailed it. I haven't had an RRA lower for awhile but they were always a lil tight in this area.

 

[komishe]

Re: Help with Commercial ar lower and Milspec upper

Maybe check it with some calipers before you go wailing on it.
Could be the finish on the upper/lower has made tolerance too tight. If that's the case, man handle it as poke said. The finish there is screwed anyways.
If you file and the finish wears off afterwards,you'll have one sloppy fitting AR with a wobbly lid.
Filings are really hard to put back where they came from.
Everything else should work fine provided you have the right buffer/spring combo for your tube.

 

[sch2046]

Re: Help with Commercial ar lower and Milspec upper

I tried to get a real man to do this for me but he couldn't get it together either. I have 3 Rra lowers, plus this one. This is the only one I can't get together. I will try a vise and see where that gets me.

 

[BigBlue&Goldie]

Re: Help with Commercial ar lower and Milspec upper

Why don't you try measuring tools first. Why fit a round peg into a squre hole for no reason? I wouldn't risk damaging a lower receiver right now..........shits worth gold at the moment.

 

[pshell]

Re: Help with Commercial ar lower and Milspec upper

Your bolt will be fine in the tube. The inside diameter "should" be the same as any military spec buffer tube. It's the outside diameter that is different. If there is a difference, it's negligible and your bolt will work.
I'm no RRA expert, but is it narrower due to ban rules? I've seen some receivers, from the ban years, that have weird stuff done to them to keep people from installing auto sears into them without major surgery.
Just a thought. You may have some kind of collectable lower. It may be prudent not to butcher it just yet.

 

[Kells81]

Re: Help with Commercial ar lower and Milspec upper

Not a ban or shelf issue to do with the ban, its something with the RRA print cause every RRA lower I have had has been a bitch to put together the first time. Especially if the upper and lower are both spanking new.

 

[greentimber]

Re: Help with Commercial ar lower and Milspec upper

Contact Rock River before you start cutting anything.