The AR-15 can do a lot with just the change of an upper, but sometimes to get the best out of it — you need to just get a new lower.
A dedicated AR-9 build is just one case since a new lower will give you a better form factor for all kinds of pistol caliber shenanigans.
From the high-end to the budget-friendly, we’ve got the best ar-9 lowers here for you!
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What Makes An AR-9 Different From A Standard AR-15 Lower
Mostly the magazine and feed ramps. You can’t fit 9mm cartridges in a 5.56 NATO magazine so you need to convert the rifle to something else — like Glock magazines.
Most AR-9s also handle ejection via a part integrated into the lower, and the same goes for any Last Round Bolt Hold Open feature.
And last but not least, the magazine release is changed to accommodate the new magazine.
Looked at individually these are small changes, but collectively they make a lower that is wildly different from a standard AR-15. And yet, they feel basically the same.
Glock or Colt Magazines? (Or Beretta, Sig Sauer…)
The first decision you should make is what kind of magazine system you want to use.
Generally speaking, I strongly recommend Glock.
While Colt SMG magazines were the original and classic choice, they are much harder to find, give you fewer options, and are expensive to replace. However, they are double-stack and are easier to load.
More niche platforms like Beretta 92FS or Sig Sauer P320 magazines are really cool but almost impossible to find a dedicated lower for. Magazine well conversion kits are great, but they aren’t a complete lower.
Glock offers a number of advantages and basically no disadvantages.
The magazines are crazy easy to find and high-quality options are on the market from Glock, Magpul, ProMag, and more.
They also come in as little as 10 rounds and as much as 50 round drums.
Plus, they’re fairly inexpensive. More mags, more shooting, more fun.
Lowers With Triggers
Most of these lower is stripped, but some do offer completed options for you to consider. Something you should keep in mind about AR-9 triggers though is that they take much more of a beating during the firing process than a normal AR-15 trigger.
Due to the blow-back operating system of an AR-9, this imparts a lot of shock into the trigger.
A standard mil-spec trigger simply isn’t strong enough to handle it long-term.
In recent years a number of brands have started to offer 9mm or PCC triggers that are designed for the extra trauma induced by the AR-9 system.
CMC, Timiney, and Wilson Combat are just a few that offer these now.
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The 7 Best AR-9 Lowers
1. Aero Precision EPC-9
One of the newest options on the market, Aero Precision has a long history of making great AR-15 lowers, rifles, and pistols. And now they offer 9mm options and will soon be offering 40 S&W, 10mm, and more!
The EPC-9 is a forward-thinking pistol lower designed for Glock magazines and optimized for long-term use.
These are budget-friendly lowers that pack in a lot of features like last round bolt hold open and enhanced parts to withstand the blowback action.
The design and styling closely match Aero’s normal lower also and include a fully forged trigger guard and flared magazine well for easier loading!
Available in Black, FDE, and OD Green — these are selling out constantly, so you might want to sign up for the Aero mailing list!
2. Palmetto State Armory PX-9
Really, there isn’t anything super special about the PX-9. It’s a functional AR-9 that gives you what you need without any added bloat.
What I like about it is that it is cheap. If you’re not sure about the 9mm PCC platform or just need a gun to treat it like an old truck, this is a perfect lower for you.
Sadly, it doesn’t have a last round bolt hold open and it doesn’t take just any AR-15 upper — it must be used with a Palmetto State Armory Hybrid 9mm upper.
Thankfully, those uppers are a great price and are surprisingly solid units.
3. Rainier Arms Billet Receiver Set
Not only is this one of the prettiest 9mm lowers ever made, but it also comes packed with features!
Lots of AR-15 lowers these days are ambidextrous, but very few AR-9 lowers are.
Rainier Arms gives us a complete ambi lower with a bolt release and magazine release on both sides of the firearm.
You also get a flared magwell for easy reloads, last round bolt hold open, and is compatible with short-throw safety levers.
And best of all — you can build this to be 9mm, .40 S&W, or .357 Sig! The lower can accommodate any Glock magazine in those 3 calibers.
It’s expensive, but you get what you pay for.
4. KE Arms KP-9
Okay, technically this isn’t on the market… yet.KE Arms recently released the KP-15 monolithic polymer lower and it is amazing.
Super lightweight, unbeatable, strong, and highly ergonomic, the KP-15 is a great lower in every possible way.
KE Arms is now working on bringing us the exact same lower but now in 9mm and using Glock magazines!
We’re crazy excited for this and expect it to be as great as the KP-15 is. But it’s hard to tell for sure yet.
Once it’s released, we’ll update with a full review on it!
Best Colt (and others) Lowers
5. Palmetto State Armory Colt-Style AR-9
Just like the PX-9, this is a functional lower. Really, there just isn’t any difference between the normal PX-9 and this except in what magazine you use to feed it.
It’s simple, it works, and it’s affordable.
6. Spike’s Tactical Colt-Style 9mm Lower
Another option that really doesn’t have anything to show off, Spike’s is a solid unit that has a bit better fit and finish than the cheaper PX-9 does.
It is still a simplistic design though and doesn’t offer anything ambi or a last round bolt hold open, but it does at least have a fully formed trigger guard.
A solid option that will serve you well!
7. Stern Defense MAG-AD9
Yes, technically this isn’t a lower — but it’s close enough.
Stern Defense’s magazine conversion is a great way to use your current AR-15 lower and just change what magazine it takes. Throw on a 9mm upper and you’re good to go!
It’s easy to install, not a bad price and lets you choose from a much larger host of magazines than just Glock and Colt.
Beretta 92FS, Sig Sauer P320, .45 ACP Smith & Wesson M&P, or S&W M&P 9mm mags — with this many options, it’s almost guaranteed you can find a magazine conversion for mags that you already have.
This was where I first started in the world of pistol caliber carbines and I loved it.
Wrapping Up
Be it a magazine conversion for a Sig Sauer P320 or a high-end Glock magazine builds to match your G34 race gun — the pistol caliber AR platform is here to stay.
An idea popular since the 1960s, we live in a golden age for firearms and this is just one of many examples.
Personally, I strongly recommend starting with a Stern Defense MAG-AD9 if you’re not sure what to get.
If you want to jump in with both feet, the Aero Precision EPC-9 is pretty awesome and for sure the best bang for your buck!
