After deciding that I need an AR in my inventory I picked up a Cavalry Arms Mark II stripped lower at a price I just couldn't pass up. This will be my first AR build and I have some questions. I'm planning on this being a distance rifle for plinking and such. I'm planning on mating my lower to a 24" Bushmaster Varminter upper. Will I have to use a special buffer spring? I've read on here that if you go to carbine length barrels that you need a carbine spring. Does going to longer barrels mean I need something different than a stock buffer spring?

This lower is marked as .223. Are there other caliber upper I can mate to this lower or am I restricted to the .223/5.56 uppers?

The other question I have is are all lower parts kits the same? Are they all of comparable quality?

Thanks for the info!

I believe the stock rifle buffer will do the job for you. It's a bit longer/heavier than the carbine set up. I believe the springs are the same, if not,someone will be along anytime to correct me.

The Varminter upper is very nice, you'll have fun with it. I'm sure you can add a different caliber upper to your 5.56 lower. 9mm will require a new hammer and bcg, as well as mag block. I'm almost certain that 7.62 x 39mm is OK in that lower also. Again, someone will correct me if wrong. There are others available, I'm not certain which though.

As far as lpk's go, there are better kits than others. I've never had a problem with Colt, Bushy or RRA. Of course, you can spend lots of cash on "better" fcu's, but if you want one to function reliable, any of the above will do.

parts are parts for lowers, but...

you might want to upgrade your trigger. I'm partial to RRA two-stage match.

rifle length buffer and spring match rifle tube/stock, and will work with mid-length gas. no need to change for longer barrel - it still has standard rifle gas port.

To echo what has been said already:

A rifle spring and buffer are for a rifle-length fixed stock and have nothing to do with the upper. A carbine spring and buffer are for the shorty fixed stocks and telescoping stocks and also have nothing to do with the upper.

If you get a carbine-length gas system upper or a 9mm upper you might want a heavier buffer (in whichever size is appropriate to your stock).

I bought a normal RRA parts kit, which was fine but the trigger stank (I'm sure their match trigger is better). I replaced it with a Geissele SSA which is GREAT (but expensive).

You may want to reconsider the CAA lower if you're looking for a long distance gun. You're pretty much sticking the heaviest upper on the lightest lower available. It may not matter since it'll most likely be benched, but I couldn't imagine the front heavy characteristics of that combination. A traditional alloy receiver with a heavy ass stock may suit you better.

2-stage triggers are a great upgrade. RRA and CMMG are popular. Bill Springfield also does trigger upgrades for cheap. Chip McCormick, Timney or Geissele makes great triggers as well.

quote:

You're pretty much sticking the heaviest upper on the lightest lower available.

I guess you're right, I hadn't thought of it that way. It will more than likely be just a bench gun though. At least until I buy another lower.

I know someone with a "Carbon 15" lower mated to just a 16" bull barrel upper...it is horribly balanced. I can't imagine a 24" bull barrel!

Aim surplus has CMMG carbine uppers on sale complete for under $600 with free 7" Troy rail forend.

http://www.aimsurplus.com/acat...lete_Upper_Half.html

I'm gonna add a weight to the butt stock and see how that works.