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Universal AR-308 / AR-10 80% Lower Receiver Jig



See the all new Heavy-Duty Universal AR-308/AR-10 80% Lower Receiver Jig

Traditional jigs use the fire-control area as the main dimensional reference. Width variations change the center to center spacing of the holes that locate the template. Other jigs on the market are incompatible with many different brands of lowers and do not account for manufacturing tolerances in width, such as with forgings. The result is inconsistent fitment, and the potential for movement during fabrication, resulting in out-of-spec features. Even so called "Universal" jigs do not work to fix these problems. Don't be fooled by the competition!

The Modulus Arms Jig takes a different approach, using standardized dimensions to locate and center the template. In order for an lower to accommodate a standard AR-308 / AR-10 upper, the lower must have a standard sized lug to center the upper. All lowers must also have a centered buffer tube mount to operate with standard AR-308 uppers.

At Modulus Arms, we have recognized these design consistencies, and applied them to our AR-308 / AR-10 80% Lower Jig. In doing so, we have the most accurate and universal jig on the market today. The Modulus Arms 80% Lower Jig uses the front take down feature on the lower to center the front, and the buffer tube mount to center the rear of the template, resulting in a jig that is compatible with any lower that can fit a standard AR-308 / AR-10  upper.

Key Features:

Universal Compatibility: Use of standardized AR-308 / AR-10 upper dimensions to locate and center the jig template results in universal compatibility and more accurate machining.
Safer and Faster: The Modulus Arms AR-308 / AR-10 Jig accommodates the use of a router, for safer and faster machining, limiting the use of traditional handheld drills to remove material.
More Accurate: The drill bit depth gauges included with every Modulus Arms AR-308 / AR-10 Jig take the guess work out of drilling into your lower receiver, minimizing the opportunity for mistakes.
Professionally Engineered Design: The Modulus Arms AR-308 / AR-10 Lower Receiver Jig is designed and CNC machined by a team of mechanical engineers with decades of experience.
Superior Construction: Precision machined 6061-T6 aluminum, with Mil-A-8625, Type II, Class 2 Red anodized finish.
View Comprehensive Features Overview here: Modulus Arms Universal Jig Features Overview
Kit Includes:

(1) AR-308/ AR-10 Template
(2) AR-308/ AR-10 Side Plates
(1) AR-308/ AR-10 Drill Guide
(1) AR-308/ AR-10 Rear Support
(1) AR-308/ AR-10 Front Support
(1) AR-308/ AR-10 Drill Bit Depth Gauge
(1) AR-308/ AR-10 Buffer Support
(1) AR-308/ AR-10 Hardware Kit

Recommended additions (Not Included):

Jig Fabrication Tool Kit

Speed Drill for Hand Held Drills

AR-308 Front Takedown Kit

*Note: Jig Fabrication Tool Kit and Solid Carbide End Mill are compatible with both AR-308 / AR-10 and AR-15 Jigs.

Product Videos

Modulus Arms AR-308 Jig Assembly Instructions 08:31

Assembly instructions for the Modulus Arms Universal AR-308 80% Lower Receiver Jig.

  • Modulus Arms A...
    Assembly instructions for the Modulus Arms Universal AR-308 80...

Product Reviews

Write Review

  1. Engineering Pinnicle

    Posted by Rasbazz on 16th Nov 2016

    To do a job correctly with no muss or fuss the Modulus Arms AR 10 80% jig is the way to go. Rock solid integrity that holds the lower receiver perfectly stable and easy to to work with too. These are things I've found synonymous that the name Modulus Arms is all about. If your looking for quality from the ground up that makes a job not a chore and come out perfect then look no further, you have come to the right place.

  2. Outstanding jig

    Posted by Unknown on 18th Oct 2016

    Used the plastic type jigs and they're cute and colorful. This set-up is solid. Take your time, get rid of the kerf.

  3. bad ass jig

    Posted by Unknown on 19th Jul 2016

    This is a VERY easy jig to use. I highly recommend this product to anyone that's on the edge of buying or not.

  4. 308 JIG Good product,

    Posted by Paul Kimura on 30th Jun 2016

    This is not a heavy duty AR-10 jig but we have to take your time working with this jig, DO NOT RUSH. Over all it is great, I have used other jig in the past but this one solves so many problems with other jigs.

  5. Good workmanship

    Posted by Unknown on 28th Jun 2016

    This jig is very well made. The design is well thought out. This is the jig to get for your AR-308 lower. The only improvement needed would be for them to introduce a heavy duty version of this jig.

  6. 308 jig

    Posted by Glen on 1st Apr 2016

    The idea and mounting of the jig are very good. The jig works pretty good as is, but takes a little time to swap between milling guides. The only suggestion for improvement would be to modify or create a heavy duty version of the 308 jig with a removable center section like on the ar15 heavy duty jig.

  7. Universal jig

    Posted by Unknown on 8th Mar 2016

    The modulus arms 308 lower is quite a bit beefier unit than say a 80%arms lower. This is awesome but the 80% Arms jig I had would not fit it so i bought the Modulus Jig. This jig is unique in the way that it holds the lower and can therefore hold a wider variety of lower receivers. The instructions are very detailed and if you follow them, everything fits correctly and the metal comes off where it is supposed to and no where else

  8. Great jig.

    Posted by Unknown on 28th Feb 2016

    This jig is very nice. Everything fits together perfectly, and nice and tight to my lower. The directions are detailed with lots of pictures so it leaves no questions. Great job.

  9. Good product

    Posted by Unknown on 1st Feb 2016

    This jig is easy to use and can help you create a very nice lower. As far as I can tell it is able to accommodate any .308 AR 80% lower in the DPMS pattern.


    Posted by Larry on 20th Jun 2015

    Assembled easy, truly universal fit. Instructions were great and simple to follow. Drill and router operations were a breeze compared to drill press and end mill bit method speaking from experience.

  11. Jig

    Posted by Unknown on 18th May 2015

    I bought this because the other jig I bought was a POS. The other jig made the router jump around and came out like shit. I am glad I bought this one because it came out perfect. Bought 3 lowers and all of them came out awesome. Great project with my sons.


    Posted by Bart on 4th May 2015