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I am looking to build a pistol caliber AR. I already have my 80% frame laying around and have a pistol caliber upper receiver coming. It can be used for 9mm and 45.

I really want to do one in 45ACP, however, I am uneducated on the mag inserts that go into the regular 556 frame.

I see that the 9mm ones are available for G17 mags, of which I have some already for my p80. But is there anything for a 45acp ar that takes 1911 Mags for example? Well or maybe greasegun mags?

I dont really want to start buying more different mags if I could avoid it and think it would be nice to have better compatability between the handgun and the PDW for mag interchangability.

Maybe someone can help out and explain, I really lean toward the 45 since I am also able to reload more for it than for 9mm.

Another question is, what do I need to look for as far as buffer and spring? I read that they are different for the blowbacks too?
 
 
I built a 45 with a dedicated Glock Mag lower last year and boy what a shooter. You're going to love it!!

I went with the Last Round Hold Open and boy what a pain in the a**. The bolt catch breaks every other outing or so and I have probably gone through a dozen bolt catches with no fix that is permanent. If the mag adapter utilizes the standard AR bolt catch, I say skip it if you have the option and do not need it.
 
Your best bet is to just stick with a 9mm adaptor that takes Glock mags or buy a dedicated Glock 9mm lower.

Trying to find a adaptor to run 1911 or grease gun mags, is going to next to impossible. If you did actually find something, it's going to be quite expensive.
A dedicated Glock 45acp lower can be had, but those offerings are limited.

I would stick with 9mm. It's the most vetted of the PPC cartridges. Using Glock mags is a no brainer.

My recommendations are the following:

1. Dedicated Glock lower (9mm, then .45)
2. Stern Defense adaptor (Glock, then the M&P version if you are a die hard M&P guy like me)
3. Endomag conversion if you want to stick with a standard AR lower. The kit replaces the spring and follower in the Pmag. The conversion requires no permanent modification to the Pmag and can be swapped back and forth at will. Just pull the guts from the Pmag and swap in the Endo 9mm kit.complete Pmags with the kit installed are also available from Mean Arms.

Also, AR9's can be finicky. Knowing that going in will help. Be prepared to trouble shoot your build if it doesn't run correctly once you get it all together.

Good luck. As I've said in other threads, I love me some AR9's!
 
Your best bet is to just stick with a 9mm adaptor that takes Glock mags or buy a dedicated Glock 9mm lower.

Trying to find a adaptor to run 1911 or grease gun mags, is going to next to impossible. If you did actually find something, it's going to be quite expensive.
A dedicated Glock 45acp lower can be had, but those offerings are limited.

I would stick with 9mm. It's the most vetted of the PPC cartridges. Using Glock mags is a no brainer.

My recommendations are the following:

1. Dedicated Glock lower (9mm, then .45)
2. Stern Defense adaptor (Glock, then the M&P version if you are a die hard M&P guy like me)
3. Endomag conversion if you want to stick with a standard AR lower. The kit replaces the spring and follower in the Pmag. The conversion requires no permanent modification to the Pmag and can be swapped back and forth at will. Just pull the guts from the Pmag and swap in the Endo 9mm kit.complete Pmags with the kit installed are also available from Mean Arms.

Also, AR9's can be finicky. Knowing that going in will help. Be prepared to trouble shoot your build if it doesn't run correctly once you get it all together.

Good luck. As I've said in other threads, I love me some AR9's!
Nah, that's too easy! I say stick with .45ACP and keep us posted on the build!
 
The endomag sounds like a pretty good idea, however its no 45 lol. Maybe the best route is to just get a few mags that go with the adapter..
 
The colt style 9mm bottom loading tension conversion blocks work awesome. Use the longer 9mm buffer or use a spacer or you will damage or break bolt hold open.. I have three of these types of ar9s and they just work. Conversion block is as much as a dedicated receiver though. They can be had at model 1 and rock river I believe.
 
EDIT............correction before any body calls it out. Yes I did Build this back in the 90's and yes they did not have Flat top receivers back then. They had the A2 receivers. I swapped out the original A2 upper for the flat top you see hear a few short years ago. Trying to keep up with the times.







I have built one of each. A 9mm using the Colt pattern SMG mags and a Polymre receiver. I would never build an AR15 with a Polymre receiver but pistol calibers have much less pressure than rifle calibers. The second Carbine is a .45acp using 30 round grease gun mags Instead of altered 16 round Uzi mags. I built this carbine back in the mid 90's. A complete SGW .45acp upper. Machined my own mag block and had to slightly open up the sides of the mag well. But not too much because I peeled the side plates off the mags. Up close was our version of anti walk pins back in the mid 90's.

IMG_20161114_214727276 (1).jpg IMG_20210510_174540222.jpg IMG_20210510_174550111.jpg IMG_20210510_175945246.jpg
 
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I would say dedicated 9mm glock lower for the first build. Ammo is way cheaper and more available. I have built a 4.5" barreled 9mm using a joe Bob's outfitters upper and lower. Added an omega9k suppressor and enjoy. Only thing that I fiddled with was LRBHO and it has been flawless.
 
i reload 9mm. Also 45acp. I have more components for 45acp and dont want to waste my spp on the 9mm. I need those for my 357.

Thats why I would like to do one in 45acp. Plus I already have the lower...
 
i reload 9mm. Also 45acp. I have more components for 45acp and dont want to waste my spp on the 9mm. I need those for my 357.

Thats why I would like to do one in 45acp. Plus I already have the lower...
Do a 45acp then. You cant build enough fun guns. I am the other way around with over 20k 9mm brass,bullets and plenty of powder. Just thin on spp
 
Torqmag made a 1911 mag insert for the AR15 at one time. Check gunbroker or eBay as they are no longer produced that I know of.
 
Use your 80% for something else and get the QC10 schizzle (when back in stock).
Dedicated, not adapted.
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