Description
Let me paint you a picture. You’re at the range, and the guy next to you is running a slick 9mm AR build. It’s smooth, it’s quiet compared to a 5.56, and he’s grinning like he just found a secret. You want in on that. That’s the exact scenario that led me to build out my first dedicated pistol-caliber AR, and the Sharps Bros Jack9 lower was the foundation. Here’s the thing—it’s not magic, but it’s a seriously solid piece of kit that gets you into that world without overcomplicating things.
The Sharps Bros Jack9 AR Platform 9mm/40 S&W/357 Sig, Black Hard Coat Anodized is a stripped lower receiver designed for building a pistol-caliber carbine or pistol. It accepts common Glock-pattern magazines in 9mm, .40 S&W, and .357 Sig, and is built to mate with standard mil-spec AR-15 upper receivers and parts kits, making it a versatile and straightforward starting point for a custom build.
I’ve built a few of these now, and the Jack9’s biggest strength is its simplicity. You’re not buying a proprietary, finicky system. This is a mil-spec compatible lower that just works. The magazine well is cut specifically for those ubiquitous Glock mags—think Glock 17, 19, 22, 31 models and their extended cousins. That’s a huge advantage because magazines are cheap, plentiful, and reliable. The black hard coat anodizing is exactly what you’d expect: a durable, wear-resistant finish that stands up to range bags and bench time. At $267.70, it positions itself as a quality, purpose-built option, not a bargain-bin part.
Building on it is a straightforward process if you’ve ever assembled an AR lower before. The fire control group pocket, safety selector hole, and buffer tower are all standard dimensions. I used a standard AR-15 lower parts kit and a pistol buffer tube assembly on my last build, and everything fit out of the box. No filing, no fussing. The lower weighs in at about 8.5 ounces stripped, giving you a good baseline for your final build weight. That said, the real engineering is in the magwell and feed ramps, which are designed to guide those pistol cartridges up into the upper receiver reliably.
Here’s a quick rundown of the key specifications:
| Caliber Compatibility | 9mm, .40 S&W, .357 Sig |
| Magazine Type | Glock-pattern (Gen 3/4 recommended) |
| Finish | Black Hard Coat Anodized |
| Material | 6061-T6 Aluminum |
| Receiver Style | Stripped Lower |
| Compatibility | Mil-spec AR-15 upper receivers & parts |
Pros: The Glock mag compatibility is a massive win for logistics and reliability. The mil-spec design means you can use a huge array of aftermarket triggers, grips, and safety selectors. The build process is familiar and doesn’t require specialized gunsmithing skills. It’s a versatile platform for three potent calibers.
Cons: As a stripped lower, it’s just the beginning of your financial and time investment—you’ll need a complete upper, buffer system, and all lower parts. You are committing to the Glock magazine ecosystem. And remember, this is a firearm receiver, so an FFL transfer is required for firearm purchases.
So who is this for? It’s perfect for the shooter who wants a soft-shooting, affordable-to-feed PCC for range fun or competition, and appreciates the modularity of the AR platform. It’s also a great choice for someone who already owns Glock pistols and wants magazine commonality. If you’re in Missouri looking to build a compliant pistol or carbine, this receiver is a logical starting point. This product is available at firearms-missouri.com for Missouri residents and nationwide, shipped to your local FFL.
Frequently Asked Questions
Q: What upper receiver do I need for this lower?
A: You’ll need a dedicated 9mm/.40/.357 SIG AR upper receiver. These are widely available from numerous manufacturers. A standard 5.56 upper will not function correctly due to differences in bolt face and barrel chambering.
Q: Does it work with Gen 5 Glock magazines?
A: In my testing, Gen 5 magazines generally work, but for guaranteed fit and function, I recommend sticking with the widely tested Gen 3 and Gen 4 Glock magazines. The slight ambidextrous flare on some Gen 5 mags can sometimes be a tight fit.
Q: Can I build this into a rifle, or is it pistol-only?
A: That depends entirely on how you register it initially with your FFL. It can be built into a pistol or a rifle, but you must follow federal and state laws regarding barrel length, overall length, and stock/pistol brace configurations. Always confirm your build plans are compliant.
If you’ve been considering a pistol-caliber AR build and value a no-nonsense, magazine-reliable foundation, the Sharps Bros Jack9 deserves a close look. Check its current availability on our site.
Reviews
There are no reviews yet.