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Running a 9mm upper on an AR-15 lower means you need a way to feed it, and that is exactly what the ProMag PM237B handles. This adapter block slips into the magazine well of a standard AR-15 or M16 lower receiver and lets it accept 9mm Colt and SMG-pattern magazines. It is the missing link in most 9mm AR conversions, and the best part is it does the job without permanently altering your lower.
The block is molded from high-strength polymer and carries steel hardware including a roller, ejector, and bolt stop, so all the working pieces that matter for reliable feeding and lockback are built right in. It drops into the magwell of a mil-spec lower and reshapes that oversized opening to properly hold slimmer 9mm Colt-style mags. Keep in mind this pairs with a compatible 9mm upper receiver, which is sold separately, and it is designed for Colt-pattern magazines specifically, so metal or polymer Colt-style sticks both work.
ProMag reworked the design so installation is fast and does not require you to knock out the bolt stop roll pin, which saves a real headache during setup. That toolless, drop-in approach is why folks running pistol-caliber AR builds keep coming back to this one. Users who have installed it note it goes in easily and plays nice with both metal and plastic Colt-style magazines.
Made right here in the United States, the PM237B balances a lightweight polymer body against durable steel internals. It is a straightforward, no-drama piece for anyone building out a 9mm carbine or pistol on the AR platform, and it is backed by ProMag's lifetime warranty. If you already have your 9mm upper and lower ready to go, this is the part that ties the whole conversion together.
You will need a standard AR-15 or M16 lower receiver plus a compatible 9mm upper receiver, which is not included. The adapter block reshapes your magwell so it feeds Colt/SMG-style 9mm magazines, but the 9mm upper is what actually chambers and fires the round. Have those two pieces ready and this block ties the conversion together.
It is designed specifically for 9mm Colt and SMG-pattern magazines, not Glock-style or other patterns. Both metal and polymer Colt-style mags work well with it based on user feedback. If your magazines follow the Colt SMG pattern, you are good to go.
No. The Quick Change Adapter Block drops into the magazine well without permanently altering your AR-15 or M16 lower. ProMag improved the design so installation does not require removing the bolt stop roll pin, which keeps setup quick and reversible.
The main body is molded from high-strength polymer to keep it lightweight, but the functional parts are steel. That includes the roller, ejector, and bolt stop, so the pieces doing the real work during feeding and lockback are built for durability.
| UPC | 708279013805 |
|---|---|
| Manufacturer | |
| Manufacturer Part Number | PM237B |
| Brand Fit | AR-15 Platform |
| Caliber/Gauge | 9mm |
| Color | Black |
| Model | |
| Model Fit | AR-15, M16 |
| Product Type | Magwell |
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