I recently got an LRB arms complete lower and look forward to building it. I am new to ARs, and after doing some research I came across terms I can't differentiate. My lower says m15sa on it, and seeing different names/numbers on the net, I am wondering if this means my lower is restricted to a certain type of build.

With any lower, are you able to put pretty much any part, barrel, buffer on it?

Do you need a certain type of lower to build a piston system or gas system?

Most lowers are pretty close to the same.  Unless your getting into pre 86 RDIAS friendly lowers for your expensive (yet very small) registered machinegun conversion they will pretty much all work fine.



As the above poster mentioned, their are larger AR-10 type varients for the .308 and similarly sized calibers.

I was a cabellas the other day and they had a Noreen 30-06 set up witch is even bigger than the AR10.

The AR-15 lower is well standardized, so if you get one, you can do anything with it that's possible with an AR-15.  BATFE regulations require manufacturers to mark "the firearm" (which is the lower in the case of the AR-15) with a caliber, but that doesn't mean you're limited to that caliber - and many lower manufacturers mark their parts "MULTI" rather than with a specific caliber.  It really doesn't matter at all.

When you build your lower, you'll have lots of choices for the bits/parts/pieces.  One important choice is what kind of stock you want to put on it.  You can go with a "rifle" type stock or a "carbine" type stock.  The rifle stock works with a standard rifle receiver extension (often called the "buffer tube" - which is imprecise and a bad choice of terms) while a carbine (adjustable) stock uses a carbine receiver extension.  Along with this, you'll need either a rifle buffer and spring, or a carbine buffer and spring.  After you decide which way to go, the rest of the parts are all the same between rifle and carbine builds.  The gas system doesn't care which kind of stock you have, and you can have a 16" barreled upper on a lower with a rifle stock, or a 20" barreled upper on a carbine lower.

Hope that helps...