Previous Post
Next Post


The following review is contributed by James.

I’m new to this whole writing for TTAG thing.  I work with Nick and Tyler at our “day jobs”, and Nick knows I am a DIY enthusiast, especially when it comes to cars and firearms.  When Optimus Defense asked TTAG to review their 80% lower, he passed the request on to me since I have both some experience with finishing them and the tools to do so (as well as a very understanding wife that doesn’t get too mad at me when I track aluminum shavings through the house).  I’ve been a firearms enthusiast for decades now, and served 14 years in the US Army and have also been a TCLEOSE certified peace officer.  Needless to say, I know my way around the AR15/M16 platform pretty well.


My initial impression of the 80% lower itself is good.  I do have a few concerns, however.  The flared magazine well is an awesome feature, but it has ridges in the front and rear that may interfere with smooth loading.  I’ll try a couple of quick reloads once I get it completed and assembled to confirm my suspicions.  My other concern is the laser engraved “SAFE” and “FIRE” markings for the selector.  I’m glad to see them, but it’s my understanding is that it may violate the ATF’s 80% definition.  Pictured are the Optimus Defense 80% lower, an Ares Armor Billet Lower, and the Tactical Machining mil-spec 80% lower.  I personally appreciate the grooves in the front of the magazine well, as that was my usual carrying point for my M4 when it was unslung, and any added traction there is useful, especially while wearing gloves.

[ED: Optimus Defense has a letter from the ATF saying the SAFE and FIRE markings are kosher. So it’s all legal and good.]


The jig, however, is top notch.  Some notable differences between Optimus’s jig and the Tactical Machining jig are: Allen-headed screws in place of the steel pins used to locate the jig with the takedown pin holes, depth gauges milled into the side of the jig to help set depth for the included drill bits and fluted end mills for each of the two-three depths required to complete a lower, and that it is clearanced to fit a beefier lower.  Don’t get me wrong, I am a fan of Tactical Machining both for their outstanding products and their voice and support for the homebuilt community, but Optimus seems to have taken TM’s proven product and made some significant improvements.


You can note the tool marks on my well-used TM jig where I had to (roughly) file it to fit another Ares Armor Billet lower I built a while ago.  The Optimus Defense jig fits the Ares billet lower just as nicely as it does their own.  The guides for the trigger pin holes and the selector hole are steel-lined like the TM jig. Using screws for the takedown pin holes allows a bit more confidence when replacing or moving the top plates, as you don’t have to worry about anything shifting in case a novice builder forgets to keep it clamped in their vise when switching them out. And the depth gauges are a handy feature as well, definitely saving time and reducing the opportunity for mistakes for the novice and experienced builder alike.


Following the provided instructions on a drill press presented a bit of a challenge, as the side load from drilling the 2nd set of 3/8” holes for the fire control pocket caused a lot of chatter and deflection.  I ended up drilling every other hole in a zig-zag pattern and then just milling it out.  This operation probably would have worked significantly better if I had only gone down a couple of millimeters at a time in each hole rather than attempt to drill the entire depth at once.  In hindsight, I believe the directions recommended this method.  So, by no means was it the fault of Optimus or their directions, more a limitation both of my cheap 8-inch Harbor Freight drill press and my lack of skill or forethought.

This isn’t a how-to, there are many of those littered across the Internet, and I will therefore skip all the in-between operations.  I have not yet assembled a rifle around this.  My original intent was to do a 20+ inch barrel Grendel build on this lower, but I quite honestly like it as a “tacticool” weapon too much to use it for a bench rifle, with the flared and grooved magwell, so I’m leaning towards swapping over my lightweight 14.5” barreled, side-charging upper onto this once its anodized or otherwise finished, and using the polymer lower off of that to build something else.

The big question with this lower, is “is it worth $229 in a market where finished lowers are running well under $100?” I honestly wouldn’t buy it.  It’s a great 80%, arguably one of the best I’ve seen or worked with, but I can’t really justify the price unless the differentiators are enough for you to want it.   I’d venture a guess that it’s comparable to the Mega GTR-3S, but even that carries a $209 MSRP, and its finished.  People like me that like to finish out 80% lowers for either political concerns or the pride of building it yourself will find the product attractive, but I think the value proposition of the lower isn’t enough to justify the price.  I’d be a buyer in the $150 -$180 range.

The jig is 3 times what the Tactical Machining jig costs, at $279 versus $90, but that price includes all the bits and mills to finish out a number of lowers while the TM jig doesn’t.  The convenience of not having to source those separately coupled with the quality and forethought that went into the jig itself is definitely worth the difference in price in my opinion, largely because I will re-use this jig and the included tooling for as long as I can, until my lack of skill or overuse destroys them.  Even then, I’ll most likely purchase one of Optimus’ jigs to replace it.

Specifications: Optimus Defense 80% Lower
Material: 7075-T651 aluminum
Price: $199

Overall Rating: * * *
It gets 5 stars for design and quality, but 1 star for price, so I’ll average them.

Specifications: Optimus Defense Drill Jig

Price: $279
Overall Rating: * * * * *
I can’t honestly think of anyway Optimus could make an AR jig better, besides offering one for an AR-10/308.

Previous Post
Next Post


  1. ATF has no definition of 80%. They have only two definitions:
    1. It is a firearm.
    2. It is not a firearm. (Some blocks of metal qualify as not a firearm like the ones shown above.)

    • And it’s all arbitrary with the decision based on the opinion of a small group within the ATF. But the ATF doesn’t care about guns, tobacco, or firearms. They care about revenue. Tax revenue… from the arbitrary taxation of random specific items handed to them to regulate. The ATF needs alcohol, tobacco, and firearms propagation to thrive. As they thrive so does the ATF by means of taxation. Really, their legislated existence is similar to the existence of a tick or a leech. They are parasites.

    • Not True for the AR15 and 1911 the ATF clearly defines what makes these firearms
      1) For the AR15 Its not a firearm if the fire control pocket, and trigger/Hammer/ selector holes are not machined.
      By machining they include permanently affixed indexing marks, such as dimples or nipples or lines engraved in it.
      STICKERS are never considered indexing marks.

      2) for the 1911 Its always been the Barrel seat, Rail, at least 2 of the pin holes cant be drilled, Most companies select the Hammer and the sear pin hole.

  2. I think the authors comment about the markings is that the ATF has stated previously that you cant have marks indicating what areas to remove, and the safe fire markings may be construed as such.

    Since there’s no definition saying how far away letters are from the hole and even the letters themselves are not a specification I would argue that the lower is still ok, but I’m not a lawyer.

    • More likely referring to the ATF requirements for minimum depth for manufacturer’s location and serial numbers – but since these aren’t required on a DIY gun, the point is moot.

  3. I am still in the research stages of planning to build my own AR, and intend to complete my own 80% lower when I do (I grew up working on our family’s machine shop). My question is, can you use the Optimus Jig with other 80% lowers?

  4. If you love to wear hoodies? so get this amazing Feel The Beat Hoodie Moreover, it has a hoodie-style collar with a pullover front closure and rib knitted cuffs to hold your wrist. All these amazing features make it one perfect casual outerwear to get compliments from your fashion friends. Discover now the best deals and amazing prices.

Comments are closed.