Question about a Rock River Lower

[Smith97z71]

Was in a local shop and have been debating on an AR build. Well they had a Complete RRA lower with just a standard trigger and 6 Position stock for $324 which was a decent price to me so I snatched it up. Anyway am considering a Grendel build and am new to the whole built it aspect as well. Was originally planning a forged lower and buying parts kits and doing everything seperately but being the first AR I figured I would keep the lower simple for now and possibly upgrade down the road. Can anybody clarify to me if the RRA complete lowers are Milspec or Commercial? Cant find much info on their site. Also what buffer and will it be compatible for a 6.5 Grendel/

Appreciated

 

[bassfishindoc]

There is no comercial spec vs mil spec lower, all are the same as long as they are from a quality manufacturer, and I would consider RRA to be quality. The buffer tube will be either mil spec or comercial spec, an easy way to check is to remove the stock and look at the tube. If it is flat on the end, chances are it's milspec, if it is angled then you have a comercial spec. Both function equally well but if you must have milspec it is an easy switch, just check YouTube. Both types will fit your lower.

 

[Smith97z71]

There is no comercial spec vs mil spec lower, all are the same as long as they are from a quality manufacturer, and I would consider RRA to be quality. The buffer tube will be either mil spec or comercial spec, an easy way to check is to remove the stock and look at the tube. If it is flat on the end, chances are it's milspec, if it is angled then you have a comercial spec. Both function equally well but if you must have milspec it is an easy switch, just check YouTube. Both types will fit your lower.

Yeah i guess I should have worded that better. What i meant was the buffer. Although it is a totally flat buffer tube and I was unaware of that distinction so I guesss its a Mil-Spec

 

[scudzuki]

Also the diameter of the mil spec receiver extension (buffer tube) is slightly smaller than the thread diameter as the threads are rolled whereas the commercial variety use cut threads which are the same diameter as the tube.

Joe

 

[AvsFan]

Also the diameter of the mil spec receiver extension (buffer tube) is slightly smaller than the thread diameter as the threads are rolled whereas the commercial variety use cut threads which are the same diameter as the tube.

Joe

+1 here's a couple of pic's for your reference. Also, I'm 99% sure RRA are commercial.

 

[drake22]

I have an RRA that is commercial.

 

[ORD]

RRA stuff is commercial size on the receiver extension/buffer tube, if it is, in fact, a complete RRA lower and not a parts gun that someone else assembled or otherwise modified. No big deal...just make sure that if you buy a replacement stock body that you purchase the corresponding "Commercial" pattern stock to ensure proper fitment. As for the flat back...don't let that fool you. Measure the OD to determine the ACTUAL size and don't just rely on the "shape" of the tube.

The buffer with be a basic AR-15 CAR buffer...in other words, ~3.0oz buffer built for 5.56/.223 but will work with other calibers. Depending on the loads you are running, how overgassed your Grendel might be (depending on the barrel you use, gas system setup, etc.), I think you'll find the basic CAR buffer too light. A basic H buffer will be 1/3 heavier and the H2 will come in at ~4.5oz. Once you get everything together, you'll just have to test it out and determine what will be best for your particular setup. With an adjustable gas block...the basic CAR buffer may be ok, but I still prefer heavier buffers as a general rule of thumb without going to low mass operating systems on the whole.

 

[blfuller]

My RRA came with a commercial diameter buffer tube. Some stocks for example the Magpul stocks that the end's are covered don't work well with the angled commercial tubes as they won't fully collapse. There are some mil spec tubes that have angled backs that have the same problem.