JMT Gen 2 80% Lowers

JMT Lower

James Madison Tactical (JMT) recently announced an updated version of the company’s 80% AR-15 lower. The JMT lowers are made of polymer and come in black, flat dark earth and OD green colors.

JMT states the company improved the cosmetics of the Gen 2 lowers, and the company also improved the strength of the part. The company lists these specific improvements/changes:

  • Extended upper fire control box sections
  • Upper left magazine well box section.
  • Webbed magazine wells L & R side (matched for MagPul) magazines.
  • Extended bolt release roll pin posts.
  • New JMT Gen2 logo markings.

The MSRP of these lowers is $99.95. The price includes a machining jig. The instruction manual for machining these lowers is here.

Richard Johnson

An advocate of gun proliferation zones, Richard is a long time shooter, former cop and internet entrepreneur. Among the many places he calls home is


  • gunslinger

    it looks like the buffer threads are polymer as well. is this true?

    • ClintTorres

      Yes, they are polymer.

      • Phil Hsueh

        Not too sure about that then, from what I’ve seen the buffer tube ring is the big weak point on polymer lowers and the polymer lowers that I’ve seen fail fail there. I would have liked to seen some metal reinforcing that area, but since there isn’t is there any other form of reinforcement or is the polymer formula good enough that it makes extra reinforcement unnecessary?

      • valorius

        Yikes. I think i’d helicoil those threads.

        • ClintTorres

          Cool, never seen those before. I would have named them “Hella-Coil”, however!

  • hking

    I don’t think I could ever bring myself to buy a %80 lower, polymer or aluminium for MORE than a finished lower. Even more so for one with polymer buffer threads.

    • ClintTorres

      Yeah those buffer threads are a concern. I have a pistol built around one of these lowers with less than a hundred rounds through it and so far, so good. We’ll see if the threads hold up over the long term.

      This is my was my first 80% build and I wanted to cut my teeth on something a little less daunting than milling aluminum. It turned out to be a fun experience. I’ll definitely move on to an aluminum 80% build soon.

      In California, only LEOs can transfer stripped lowers as “pistols”.

    • david

      The point if an 80% lower is NOT to save coin. Although, I can’t figure out the point of polymer lowers since they have been shown to be inferior to aluminum.

      • ClintTorres

        The point of a polymer 80% lower is that you can use JB weld to fix your screw-ups…don’t ask me how I know this.

      • Cymond

        Also, the point of a polymer lower is for people who are “equipment challenged”. There’s a video out there somewhere of a guy completing an 80% lower using a Dremel.
        When I started looking into 80% lowers, everyone said that is possible to finish them with a drill press, but you should really use a mill. Now here’s a lower that a drill press is the intended method, and it is possible to use a Dremel.

        • ClintTorres

          I started out without a drill press thinking I could use a hand drill and a dremel but soon discovered that it wasn’t going to work out. I could not prevent the bit from walking despite my best efforts.

          I ended up getting a drill press at Harbor Freight for under $60 on sale with coupon and it was well worth it. I also shelled out for a $16 drill press vise and the entire rig has worked out well. Still used the dremel for final fitment however. I did not try to use the drill press to mill. Just drill holes close together then dremeled to a good-enough finish. The pockets don’t have to be square everywhere.

          Part of why I went polymer was just to see if it could be done and produce a working/reliable firearm. The final product seems solid. There’s less play than with my other (frankengun) ARs between between the upper and lower (LMT lower with Vltor MUR upper and PSA lower with BCM upper). Selector and take down pins are nice and tight.

          Only issue I had was FTEs that was fixed with an O-ring around the extractor spring but, obviously, this is not an issue with the lower.

          Only time will tell if the polymer is has enough strength and toughness.

          • guesty Guest

            Key to getting perfect holes locations with a drill press is to mark the exact center using a tiny diameter drill in a pin vise to start the hole.

      • valorius


  • valorius

    How much less does a polymer lower weigh than an aluminum lower, in ounces?

    • Steve Truffer

      Depends on the polymer used, and forged vs milled. Seems to be 3-4 ounces, unless you throw in TN Arms’ Clear lower (though they state outright it is not made with military use and kill tests in mind)

      • valorius

        Thanks. 1/4 lb in weight is a lot.