Hi guys I am a newbie at this but I just got a lower label multi caliber and I will like to do a 9MM AR15 type rifle, I got several builds done but all been 223, my question is a regular lower will work with 9MM magazines and will it work with an upper in this pistol caliber?

You will need a magwell adapter. I think colt mags work. I built mine for glock mags

You have a few options. First is a magwell adapter that can either be pinned in place or drop in. The second is to buy olympic mags(or something like them) that use the full sized magwell. It is worth saying that apparently olympic arms is still operating although they are trying to sell themselves. If you used their magazines you would need to use their upper. The third option and probability the best if it is going to be a dedicated 9mm gun is to keep that lower for something else and buy a lower setup for pistol caliber. You can get ones that are machined to fit the colt style 9mm mags or various other magazines. Now lowers that take glock mags are becoming far more common although you have a few for other magazines as well(and someone working on one that will work with mp5 mags for some reason).

FYI the marking on the lower mean nothing. The lower could say 5.56, multi, 6.8, 6.5, etc and you can run whatever upper you want on it.

If I was doing it I think I'd just buy a glock lower or one of the lowers that takes colt ar 9mm mags that has a smaller magwell.

Yea PSA Sells a glock lower for 9mm. However using the magwell adapter would be the cheapest route imo.

Use the Colt style mag well adapter with your multi lower (as already mentioned).
Typically need a 9mm buffer also. Make sure you get/use a ramped BCG. You can build your upper or buy one ready to go. I have no affiliation with KAK or 9mm AR, just providing examples.

AR15 9MM MAG WELL ADAPTOR FOR COLT / UZI STYLE

AR15 9MM CARBINE BUFFER


9mmAR has adapters, barrels, mags and complete uppers.

C Products 9mm AR mags and ASC 9mm AR mags and  MetalForm 32rd 9mm AR-15 Mags work well

Since I'm already invested in the Glock platform, I went with a Glock-style lower from PSA. If you're wanting to build a Colt-style 9mm, there is a wealth of information on this website...just start browsing and you'll be amazed at what you learn.

I just built a 9mm pistol and went with a dedicated CMMG colt style lower. I found the CMMG complete lower on sale a couple of weeks ago for $289. It was within $40-$50 versus getting another stripped multi lower and mag block.

When I priced getting a mag block (either RRA or Hahn), they were anywhere from $155 to $200 for them, then add the cost of a stripped lower (average of $50 after transfer fees) and a 9mm buffer ($25 average) I was up to about $230. That price didn't even include the lower parts kit or buffer tube. Now the price difference of $40-$50 was with the Hahn mag block. The price would be about $175 if you went with the Kak mag block. As you can see it was almost as cheap and easier just to get the complete dedicated lower. The average price for a complete dedicated Glock mag lower from Palmetto State Armory is $200.

I built my upper to get exactly what I wanted. I wanted a semi clone of a Colt 635. I all ready had an A2 upper along with carbine hand guards sitting around to use. I ended up getting a 10.5" barrel with FSB from Rock River Arms and a CMMG 9mm BCG from 9mmAR. Barrel was $205 and BCG was $170.

I built my 9mm SBR many years ago, before dedicated lowers and "wrist braces" were a thing.

I tried to go cheap with the C-Products mag block, it was not reliable.

Switched out for the Hahn, it is held in place by the bolt catch. Therefore, to remove the mag block I have to drift out the bolt catch pin. This would make it a dedicated lower.

All problems ceased with the Hahn, I am using C-Product 32rnd mags.

The CP mags do not activate last round bolt hold open. They are supposed to though I believe.

I've never tried metalform but back then they were the best.

Last round BHO isn't that big of a deal to switch out all my mags.

I use a spikes buffer also, BTW. Everything else is the usual stuff in the lower.

Upper is 7.5" Colt barrel, Colt ramped bolt carrier. As I said, I built this at least 10 years ago, before different companies made it as easy as it is today.

Thanks a lot guys I believe I need to do my homework before I star this projects as the options are endless, however if I already have the lower built the adapter way may be the way to go.
Again thanks a bunch, this site is full of knowledge and helpful folks.

Most people will recommend using the Hahn mag block adapter for best reliability. They run anywhere from $175 to $200.
Kak sells their adapter for $100 Kak maga adapter

CMMG Complete upper, Rifle Gear Lower, RRA Mag Block, ASC Mag's and a Stag Lower Parts Kit.

If you want the best reliability get a dedicated 9mm lower for COLT pattern magazines.  They are available from Primary Arms for $142.46.  The dedicated lower is made by CMMG.  There are lots of advantages to using a Colt dedicated lower.  First the Colt pattern lowers use a feed ramp (Glock lowers do not).  The LRBHO is the same as the AR-15.  The mag latch is the same as the AR-15.  Colt mags made of metal are readily available and cheap.

Here is my AR-9 Colt lower.  I bought a complete lower from PSA but PSA no longer sells Colt pattern lowers.  The dedicated Colt lower PSA sold was a CMMG lower.