AR question/help

[cecILL]

Hello, starting first AR build.
Have lower completed and now in search of the upper and stock.
Would like to build short and legal.
Would like to chamber in 9mm. Do I need a dedicated 9mm lower or is it possible to use a .223 lower? Assume there must be an insert of some sort for the 9mm magazine?

Also, when searching the various sites, stocks are sold for "commercial" or "military" lowers. Difference?
And, any other advice on brands, things to avoid, or tips appreciated.

[trigger643]

You can use a conversion block. Some are staked in permanent, but others, like the one from brownell's are removable. I've used the Hahn conversion block, and it works as advertised.


http://www.brownells.com/rifle-parts...-prod1548.aspx

[Dragline45]

Without having to get a $200 tax stamp and have it registered as an SBR, the shortest barrel length you can go is 14.5" which requires a 1.5" flash hider, comp, or break to be pinned to bring it to the 16" requirement. Consider most barrels are 16", but most have a 1"+ flash hider or comp, that brings it in actuality to 17"+. The 1" difference might not seem like alot, but it really does make a big difference in tight spaces.

My 14.5" mid length AR with a 1.5" Battlecomp and 12" LOP Magpul Fixed Carbine Stock is about 32.75". While it would be shorter with a fully collapsed adjustable stock, I live in Massachusetts where they see collapsible stocks as an "evil" feature so I am forced to go with fixed.

[Sharkbite]

Ive got a Pro-mag block in a standard lower....doesnt run for carp. Dont waste money on one of those. Ive heard good reviews on the Hahn magblock

Im considering just getting a dedicated 9mm lower and be done.

As noted above 16" is the shortest barrel length without doing the NFA thing. My gun is a 9.5" barreled SBR. When i screw the suppressor on it is still shorter then a "standard" barreled AR. Plus its super quiet. Now if i coud get it to run more then a cpl rounds without FTF id be much happier

For a dedicated lower...RRA seems like a good choice

[tahunua001]

I use the block from model 1 sales, works good but you need to use metalform/colt mags... the modified uzis, Cprod, and other cheapo mags don't do well in them. promags work but the last round bolt catch wears out really quick... or at least they do in mine.

[marine6680]

Mil spec vs commercial stocks has to do with the diameter of the tube.

Commercial ones are slightly larger in diameter, so that forces a different model.

The size difference is because of how they are made... Both work but more stock options are available for mil spec size tubes. So get a mil spec... And make sure its also mil spec material, 7075 aluminum. Some cheap mil spec tubes are mil spec on dimensions only, and use cheaper alloy.


What's the reason for wanting 9mm? Mags are a little less convenient, and 223 can be gotten for not much more than 9mm right now.

[cecILL]

Thanks for the help, guys!

Ok, the commercial vs military tubes are different diameters. Does this mean there is a difference in the threads on the lower?

The reason for 9mm is I already have a Colt HBAR in .223. Bought a couple Anderson lowers at a local gun show for a decent price ($60).

Been looking at the RRA collapsible butt stock. And probably the RRA complete upper w/ 16" barrel. Is the CAR or mid-length upper preferred?

Always looking for advice.

[tahunua001]

cheap 9mm is about $12 per 50 right now. the cheapest I've seen 223 is $6 for 20, that's an extra $6 every hundred rounds downrange, $60 every 1000, etc...

for $60 I could buy a lot of little gadgets.

[Sharkbite]

Both tubes have the same threads and will fit the lower. The difference is in the outside diameter and hence the different stocks needed. Choose the stock you want...see what diameter its made in and buy the correct tube

As for caliber selection, like you, i already had a cpl 223's, one 300blk and a 22lr. So 9mm seemed like the next toy. With my can on it is SILLY quiet. Everytime someone on the range sees it there jaw drops. Once i get it running it will prob be my fav plinker

[marine6680]

The threads are the same, so no worries between them other than stock. They use a different method of cutting the threads. Commercial tubes being larger have the threads cut in. The mil spec tubes have threads with an outer diameter larger than the tube diameter, I believe they roll the tube in a die that rolls in the treads.

With a 16 inch barrel in 5.56/223 I prefer mid gas. It provides the proper dwell time for the system and is easier on the parts.

Most 9mm ARs are blowback, so that is not a concern, a proper bolt and 9mm buffer should work well with a 16in barrel. A shorter barrel may need a little less weight in the buffer, but I don't run a 9mm, so that is speculation based on my knowledge of various blowback guns.

As was mentioned, 16in is minimum length for a barrel, unless you bother with the paperwork and tax stamp process.

You can build a pistol lower, outfit it with a Sig arm brace, and use a shorter than 16 inch barrel, as a pistol does not have a barrel length requirement. You would have a close approximation of a SBR without the need for the paperwork involved.

I have yet to find a need or want for such a thing, I am fine with 16in barrels in my rifles, but if you want a short barrel, a 9mm is a good way to go, less hassle from shortening the gas system that is required in a 5.56.

[cecILL]

Thanks again. Questions (for now) answered. Looks like a 16" CAR 9mm upper.

Why 9? So much easier to reload than .223!

[cecILL]

Another question. The Hahn conversion block comes in top or bottom configurations. Is one preferable than the other?

Where to order magazines? What brand of magazines?

[tahunua001]

buy metalform or colt mags. stay away from the cheapos. cheapest I've found the good ones is CDNN.

[cecILL]

Looks like the bottom loading Hahn block from Brownell's is out of stock.

Trigger, which version did you use?