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View Full Version : Build AR a 9mm or a .40? Pros and Cons.


littlerocket
02-28-2010, 9:41 AM
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
02-28-2010, 10:26 AM
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
02-28-2010, 11:27 AM
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
02-28-2010, 11:57 AM
RRA is doing factory .40 that don't use Glock mags now.

Josh3239
02-28-2010, 11:57 AM
Are thoes available right now?

badfish71
02-28-2010, 2:11 PM
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.:83: in any case, i would say 9mm. seems to be more available parts.

Ding126
02-28-2010, 2:18 PM
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
02-28-2010, 2:43 PM
Hmm, wonder when they released those. That is really cool. Up till then you were limited to pretty much Olympic.

dachan
02-28-2010, 2:52 PM
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
02-28-2010, 3:07 PM
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
02-28-2010, 3:11 PM
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
02-28-2010, 3:12 PM
DACHAN

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

littlerocket
02-28-2010, 3:26 PM
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
02-28-2010, 3:31 PM
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
02-28-2010, 3:33 PM
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.

faust858
02-28-2010, 3:34 PM
I didnt know they are making a 40cal upper for the AR. Could you just buy a 40cal upper, and do barrel swaps so it can use 9mm, and 357sig? I know I can do that with my Sig2340 with new barrels. Just wondering. *thinks about that unbuilt lower I still have*

Josh3239
02-28-2010, 3:35 PM
RRA and Olympic offer dedicated lowers. The RRA uses Colt mags, the Olympic uses Glock mags. You can also buy an 80% dedicated lower for either sten mags or for colt mags.

Lone Wolf and BazookaBros both offer a dedicated .40 lower IIRC.


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

Josh3239
02-28-2010, 3:36 PM
In addition to changing the barrel you'd also have to likely change the BCG, mag block and magazine.

I didnt know they are making a 40cal upper for the AR. Could you just buy a 40cal upper, and do barrel swaps so it can use 9mm, and 357sig? I know I can do that with my Sig2340 with new barrels. Just wondering. *thinks about that unbuilt lower I still have*

quiksilvern7
02-28-2010, 4:10 PM
I thought olympic receivers and guns were illegal in CA?

Josh3239
02-28-2010, 4:14 PM
Make and model both have to be banned. Only Olympic AR15s, Car97s and PCRs are banned. That is why we call it off-list, because the model is not on the list.

Glock lower made by Olympic Arms is model K9-GL.

gunrun45
02-28-2010, 8:13 PM
Or you could buy a MGI lower with glock mag well (2 sizes, 1 for 9/40 and 1 for 45/10) and your Oly upper.

You could theoretically buy the MGI modular upper, have it drilled for the Oly ejector (universal ejector in Oly's for all pistol calibers) and different barrels to shoot a WIDE asortment of calibers using glock mags...

There is always another way to slice the pie boys!!

I have owned the Oly uppers in 9mm, 357 sig, 40S&W and 45ACP. Anything but 9mm takes some pain and suffering in the magazine department. You CAN modify STEN mags to feed the other calibers, but you have to play with them a bit. They are a sweet shooting alternative. I sold my 40S&W upper unfortunately a few years ago to a CHP friend.

g2jap
02-28-2010, 8:29 PM
The Lonewolf dedicated ar glock lower takes both 9mm and .40 glock mags. It also uses a majority of the uppers that are out there with a little modification. I just got the confirmation that mine is shipping to my FFL and will post some pics of it when I get done drosing it.