Build AR a 9mm or a .40? Pros and Cons.

[littlerocket]

Hi all, first of all this site is a great resource, I have learned a great deal towards my first build.

Now my question, I searched, but couldn't find anything. If you were to build a pistol round AR, which would it be? 9mm or .40? I'm sticking with pistol rounds because they are significantly cheaper than rifle. I am going to build a .223/5.56 one as well and I already have a 10/22. What are the Pros and Cons of each? I guess what's important to me is Accuracy, Ease of use/maintenance, Cost in that order. But I will welcome all comments. Thanks in advance!

[pacrimguru]

i don't have any experience in .40, but i'm very happy with my 9. (see link in my signature)

as for accuracy i'd imagine they would be similar, use and maintenance should be the same as well, cost of ammo on the 9 is cheaper and i'm not sure about the rifle build though. i never looked at .40 parts - although i think there are less options. look at magazine options and factor that in. those always end up costing a lot.

[Josh3239]

9mm Pro: Easy to build, cheaper to shoot
9mm Con: Limited amount of parts, magazines and their blocks can be finicky

.40 Pro: Don't think there is
.40 Con: Even more limited parts, no 10rd mags unless you use Glock mags but those lowers are tough to get, ammo more expensive

[NSR500]

RRA is doing factory .40 that don't use Glock mags now.

[Josh3239]

Are thoes available right now?

[badfish71]

yeah you get cheaper ammo but you end up shooting a lot more also. at least thats what happen to me when i got one. go shoot some steel with it and you'll find out. its like shooting as a kid in a shooting gallery. in any case, i would say 9mm. seems to be more available parts.

[Ding126]

I have a 9mm AR and like it ( 2nd one ) and just ordered the RRA .40 upper..The RRA tech says you will need everything the 9mm rifles require

HD buffer
same 9mm style mag block

The mags are RRA mags...I'm sure in time C-products will have them as well...My 9mm Colt mags seem to work with the .40 ammo....I'll need to give them a try for function

[Josh3239]

Hmm, wonder when they released those. That is really cool. Up till then you were limited to pretty much Olympic.

[dachan]

RRA is doing factory .40 that don't use Glock mags now.

According to RRA, as of last Wed, these won't be available till mid-summer. They are still working on the magazine and mag block design.

[Ding126]

Here is the reply from BJ @ RRA

"The 40s+w will use all the same parts as the 9mm and use its own proprietary mag by us but right now there is no 10rd. on the design board."

[Ding126]

Are thoes available right now?

I pre ordered my upper ...when it gets here..it gets here. RRA made it sound like they are ready to ship..just waiting on magazine production

who knows..but I can wait

[Ding126]

DACHAN

Can you order a LAR-40 lower for me? Price?

[littlerocket]

Thanks for the replies folk, great info. So would you say the 9mm design is fully hashed out, so to speak? Should I wait a while for further design improvements? I've seen the RRA kits and those are the ones I'm considering.

[Ding126]

Since we are in CA..your basically limited to a standard AR lower ( OLL of course ) and a mag block from..spike's, RRA, CMMG & Hahn are the few that come to mind...

I'm not sure if there is a dedicated OLL in 9mm

Can some one chime in on that?

[Josh3239]

In my mind, the 9mm AR is an easier, safer build. An AR .40 is a very fun thing to have but it really doesn't offer anything over the 9mm that I can think of. RRA usually puts out good products but I wouldn't want to put my money in a project that has no reviews and hasn't been released.