AR 9

Magwell.

To use Glock mags you have to have a ramped BCG. And I believe (hopefully someone will correct me or confirm this) the Colt mags can use standard AR9 BCG's or also ramped BCG's.

You can go two ways on the lower, you can get a dedicated lower where the magwell is reduced down to the dimensions of the magazine chosen, or you can use a standard AR15 lower and get a magwell adapter at an extra cost.

If you want last round bolt hold open (LRBHO) you can do it with either Colt or Glock magazines but need to pay attention at a few things on the Glock side of things. The Colt pattern AR9s come standard with LRBHO, but for Glock patterned AR9's it is additional proprietary lower OR you can achieve it with a proprietary upper and a standard Glock lower. Each of these I understand requires some adjustment to get to work right.

I've always wanted an AR9, never really got around to it. Although I've owned Glocks, it just wasn't useful for me when I can shoot the Glock or the AR15's I already own.

Its still a good option if you have the extra cash. I have a 22LR conversion on my AR15 and its way cheaper to shoot...

Colt developed, and released an AR style 9mm carbine in the 1980s They used a straight steel 32 round magazine. The design was successful, and Colt makes a run of these occasionally.

A more recent development was a similar carbine in 9mm that uses a Glock pistol magazine. This appears like an AR, but originally the magazine release was not AR style, and they had no Last Round Bolt Hold Open,(the colt has always had identical AR controls, and operation just like a higher power AR). Recent Glock style ARs have fixed the mag release issue(now the release is in the same place as an AR), and a few Glock carbines have a LRBHO, but most still do not.

The decision which style you want to use.is yours. Both are reliable, both magazine styles are easy to find. I chose the Colt style. The 32 round Colt style magazines are cheaper than the 33 round Glock mags, but can usually only be found online.

To add... it is the magwell/lower that determines what mag you use. The 9mm AR bolts being built today are hybrid, meaning they work with either style magazine. Make sure you get a hybrid bolt, or that your bolt matches the magazine style. All new bolts are also ramped in the rear at the bottom. This allows them to work with any hammer style, Mil-Spec, or not.

This works well:

https://www.thehighroad.org/index.php?attachments/7e203e2a-71d8-4454-929f-9047ac5e3529-jpeg.776957/

It’s an insert into the standard mag well that allows the use of Glock magazines. It does require a Glock compatible BCG, and it provides a last round bolt hold open feature without requiring a unique upper to support.