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Universal AR-15 80% Lower Receiver Jig



Please see the All New Heavy-Duty Universal AR-15 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-15 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-15 uppers.

At Modulus Arms, we have recognized these design consistencies, and applied them to our AR-15 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-15 upper.

Key Features:

Universal Compatibility: Use of standardized AR-15 upper dimensions to locate and center the jig template results in universal compatibility and more accurate machining.
Safer and Faster: The Modulus Arms AR-15 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-15 Jig take the guess work out of drilling into your lower receiver, minimizing the opportunity for mistakes.
Professionally Engineered Design: The Modulus Arms AR-15 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 AR-15 Jig Features Overview

Kit Includes:(1) Template

(2) Side Plates
(1) Drill Guide
(1) Rear Support
(1) Front Support
(1) Drill Bit Depth Gauge
(1) Buffer Support
(1) Hardware Kit

Recommended additions (Not Included):

Jig Fabrication Tool Kit

Solid Carbide End Mill Bit

Speed Drill for Hand Held Drills

AR-15 Front Takedown Kit


Product Videos

Modulus Arms AR-15 Jig Overview

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Product Reviews

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  1. Jig worked great

    Posted by Unknown on 2nd Nov 2016

    I just finished my first 80% lower and everything worked great. I have installed the lower parts kit and going to start on a second 80% lower. I just took my time and kept thinking of what I was doing and it came out perfect. It looks as though it was milled on a CNC milling machine.

  2. Easy breezy quality product

    Posted by Peter Sices on 30th Aug 2016

    First time AR15 builder. Watched the video and read the manual. Got the fabrication kit with the bits and mill as well. Very well written and easy to follow instructions provided. Very easy to put the jig together and drill/mill. Just follow the instructions and proceed carefully. My receiver came out perfect!

  3. Hmm What a Jig

    Posted by Larry on 8th Jun 2016

    When I received the jig and 80% lower I had to go online and view your video to put it together. When I got it put together it appears that This is made very well. than that I would recommend this jig.

  4. great product

    Posted by Unknown on 14th May 2016

    The jig is designed great. A greatly more universal jig than others. Cuts the billet lowers I order great. I recommend getting a good set of transfer punches and with a drill press you don't have to worry about eventually boring out the holes in the side plates. Punch the center of the holes and remove it the side plate and drill.

  5. the perfect jig

    Posted by alex mejia on 13th Apr 2016

    The quality ,fit, and outcome was great. Really liked the checklist in the packing. And their customer service was great at least for me. Totally recommend this jig.

  6. Excellent

    Posted by Unknown on 9th Apr 2016

    I bought this to do some polymer lowers. I spent more time putting the jig together and rearranging the parts than I did milling and drilling lol. I used a cheap 2hp router from Harbor Freight and a endmill from Amazon. Came out perfect!

  7. It works as promised

    Posted by Unknown on 28th Jan 2016

    It's pretty easy to use. Things I would change would be written instructions should be included, the template elongated at the rear (to use a router with a larger base) and I wish i had bought the heavy duty jig. Don't get me wrong, I can still use this jig for more receivers, but with each receiver made equals more wear and tear on the aluminum jig. I feel the heavy duty steel jig will outlast the aluminum, but if you're only doing a couple receivers then the regular jig works just fine.

  8. Best Jig I'be ever used

    Posted by Boggz on 25th Dec 2015

    I've messed up a couple lowers before using other jigs, buying crappy x y vices, and just being rushed. This thing is AWESOME!!! I finished a lower the night I got it and it looks just like my complete lowers. It is a bit of a hassle with all the screws but I just use a drill driver to do most of the work and hand tighten with an allen wrench. I look forwad to finishing many many more lowers. I only give it 4 stars because of the number of screws used in setup and the aluminum side plates. If I were to buy again I'd get the heavy duty one and never look back.

  9. Good jig for one time use!

    Posted by Daniel on 14th Dec 2015

    Awesome jig and outstanding quality, but if I were to purchase again I would spend the extra for the heavy duty steel plate version. I am satisfied for my first AR build but will be purchasing the stronger jig for my future builds. Thanks.

  10. Took less time than I thought

    Posted by gregory on 29th Nov 2015

    The jig worked pretty well and i was done in a little over an hour. This wasnt my first time making a lower and have used a different drill press style jig. Pleased with the results

  11. Great product

    Posted by Unknown on 27th Nov 2015

    I like this jig because it adapts to many different lowers form different companies.

  12. GREAT!!

    Posted by Pat B on 10th Nov 2015

    After trying 3 drill type jigs and buying a new drill press, I bought a router and the Modulus Arms jig and it is the ONLY WAY to go! Don't waste your money on the drill press. A $100 router and this well engineered jig works great. Clean, precise cuts!

  13. Awesome Jig

    Posted by Mike on 13th Jun 2015

    This jig worked perfectly for both a polymer and a Modulus lower. Takes a little time to set up and convert between stages but worth it given how accurate it is. The instructions were easy to follow and the end result were lowers that fit perfectly with lower parts kits and uppers with no additional tweaking needed. Only recommendation is take it slowly and make sure the depth adjustment on your router is tight as I had it slip on my router a couple times.

  14. STOP RESEARCHING! Buy this one!

    Posted by Rich on 8th May 2015

    I overly research EVERYTHING and this was no different. I considered nearly a dozen different jigs and in the end, only one other even came close. The final selling point of the Modulus jig was the router shelf, excellent instructions, side plates that can be flipped around if they become oversized, and replaceable individual parts. The only thing this is missing compared to other jigs is drill bushings, but the fact that you can flip the side plates negates that.

    My tools were a Bosch Colt palm router as specified, a 6" HF cross slide vise on my drill press (I cleaned and polished it up...it's pretty darn tight now) , a 6" Irwin drill press vise, and the proper bits. You could do it as shown in the instruction with a hand drill, but I wouldn't trust myself. The Irwin vise was clamped to my workbench to do the routing on.

    I ended up chewing through several end mills. First was a 4 flute AlTiN high helix, which snapped off a good chunk of the tooth after only a few passes. I later found that this was definitely not the right bit to be using in Al. Next was a 3 flute solid carbide, which was a huge improvement. This is where I learned that you need to be VERY careful when nearing the point at which you break out of one drilled hole and into another. When applying that side pressure to the bit and it breaks through, even that small "jolt" as the bit travels free for a moment can be enough to break the carbide. This leads to a vibrating bit and a much more difficult time removing material.

    The final bit was a 2 flute ZRN coated carbide end mill. My understanding is that ZRN is the coating of choice for milling aluminum and I would concur. It definitely felt slicker and was not picking up an materail deposition. Each of these bits were found online for under $30. I did not use the 4 flute solid carbide end mill available through Modulus, but I felt that 2 flute bits were a more effective and easy-to-handle choice.

    The Modulus lowers I was milling out were 7075 Al and based on other reviews, the 6061 lowers might not be as hard on end mills.

    Assembly and function testing went smooth. I did find that my safety selecter holes were a bit tight and required buffing out with a rubber wheel to allow an easy to operate selecter and for the detent to lock positively in place. I had this on all 3 Modulus lowers I have done and this is with 3 separate drill bits (Dewalt, Snapon, and Vermont American) and 3 different brands of lower parts kits (DPMS, Del-ton with 2 stage trigger, and PSA.) Part of the detent not clicking in was material from milling in the hole, which I cleaned out with an 1/8" drill bit and just spinning it in my fingers.

    Total time to completion on the first one was about 3 hours. I am extremely satisfied with my jig and lower and would recommend to anyone. The fit and finish of the jig, as well as the finish produced exceeded my expectations. Their lowers are exactly what they should be and I am very glad to have spent my money here, especially with the veterans discount.

  15. Success on first try!!!!

    Posted by Unknown on 4th May 2015

    This was my first attempt to complete an 80% lower....after reading reviews from many different jig suppliers I chose Modulus Arms. Bottom line is my first lower came out perfect because the jig design is great and the written instructions are very clear and detailed with lots of photos. I followed everything precisely and I couldn't be happier with the results!

  16. Very pleased!!!!

    Posted by Julion on 24th Apr 2015

    I recently purchased the modulus arms jig and I'm am very impressed with the product and the service of this company . My package came on time with no delay and I am very pleased with my purchase. Overall this baby worked like a charm thanks guys!!!!!

  17. Great Jig

    Posted by Unknown on 1st Apr 2015

    The jig works great and is fast and easy to use after you figure out how to use it. The instructions are not very helpful.

  18. Much better experience than traditional jigs

    Posted by Sofia on 1st Apr 2015

    I learned how to work my lower using the jig that came from the company that made my lowers and after the first one I was left wanting... I spent some time investigating other jig options and Modulus quickly came to my attention. The Drill plates immediately made the initial at-depth drilling experience a lot less stressful and the Router Top milling was breathtakingly easier.

    Initially I had purchased the jig by itself, hoping to use my existing endmills, but the elevated height over the buffer tub required the additional purchase of the Modulus Endmills, which I would recommend to anyone considering this purchase. Finding endmills the length required will not be easy. Save yourself the shipping and get them when you get the jig.

    The youtube demonstration videos (just search modulus jig on youtube to find them) were invaluable. I watched them all twice through before starting my lower and didn't need to go back to them once I started. They are very verbose on what you really need to know without dwelling on things you don't.

    Great work Gentlemen.

  19. Drill guide

    Posted by Unknown on 1st Apr 2015

    Love the jig wish you would bring back the older style 10 drill guide

  20. Top Notch

    Posted by Damon on 19th Mar 2015

    Excellent jig, very easy to use. Would highly recommend.

  21. Too Easy

    Posted by Brian Myers on 16th Mar 2015

    Finished my first 80% lower with this today it was easier than I expected. I would buy this jig again.

  22. Reviewed them all, timely processing, Excellent

    Posted by D Bear on 12th Mar 2015

    I did indeed do a great deal of due diligence, researched products and reviews of products - I am not disappointed. This product appears to be the Ultimate in Jigs for aluminum lowers, I hope they expand their product line and come up with an equal or better 1911 jig.

  23. The best out there

    Posted by Unknown on 12th Mar 2015

    This is hands down the best jig you can buy ! Very easy to use and lots of support .

  24. The best designed Jig I own

    Posted by Ken on 1st Mar 2015

    Great Jig. Extremely well thought out. I own 3 other jigs and wanted to try this one and Routering. I have a mini-mill and I think this jig is great with a mini-mill - I tried the router but found the mill easier (just me) to control. The mill is slower but to me its much smoother to control. Do yourself a favor and buy the carbide mill bit here at Modulus Arms - You want a 4 inch long cutter with only a 1" length of Cut. Hard to find and the ones here are reasonable. Any longer length of cut and you will cut up your jig. Also get some spare 8/32 1/2" long cap screws as if you drop one you want to have spares. Weak points is the attractive red finish wears easily compred to other jigs I own, but if your careful shouldn't matter. I think I might get some spare replacement parts for it as I plan on using this a lot. I debated to get this jig because of price, but it is worth the money.

  25. Universal is awesome!

    Posted by Unknown on 23rd Feb 2015

    .It worked on all of the lowers I have acquired over the years. Was shocked it fit them all.

  26. Great looking Jig!!

    Posted by Unknown on 19th Feb 2015

    Can't wait for the next product. Hoping they make a 1911.

  27. Nice jig!

    Posted by Ricardo Christian on 19th Feb 2015

    I bought this jig so that I could finish my first AR build. I have built AK's in the past so I wanted to try something new. I bought a blank receiver and I needed a jig to finish it but I didn't want to buy expensive tools to accomplish it. I also didn't want it too cumbersome in order to complete. I read about this jig and decided that for the price, it would pay for itself. I didn't expect much from it since it was pretty cheap. When I received I was extremely shocked of how excellent the quality was and how trouble free and fool proof this jig was. The instructions were so easy to follow and the finish was flawless. I highly recommend this the everyone.

  28. ONLY jig worth getting

    Posted by Reuben on 9th Feb 2015

    I finished my first build with this and it is awesome! I took my time and watched the video a few times until I knew the steps by heart! They have a tool kit that is a must also! You drill seven holes and mill/route them out and that is the fcg! Wow talk about easy! I ordered a couple more lowers today just to have more fun, dont question, just order NOW!

  29. Great Jig...

    Posted by Michael Stahl on 9th Feb 2015

    I bought this jig on recommendation from a friend who told me its the only one he'd go with. He wasn't wrong. The jig is universal and very easy to setup and use. They take all the guess work out of it. Make sure you get their Endmill Bit... its hard to find one this long!

  30. cool prodcut

    Posted by Terry on 7th Feb 2015

    I saw this on slickguns and thought I would give it a try. It was pretty straightforward and fun project.

  31. best jig I've seen.

    Posted by Unknown on 3rd Feb 2015

    This is the easiest jig I've used. Milling with the router was way easier than a drill. The pocket milled out was as clean as any of my production lowers. This would have 5 stars if it came it steel. Then it would last pretty much for ever. Hopefully Modulus sells replacement jig pieces. I plan on using this a lot.

  32. Very good jig

    Posted by Unknown on 24th Jan 2015

    Jig was very easy to use and gave good results in milling two receivers so far, but you can only expect so much from tooling made of aluminum. I do wish, however that they would make this jig in steel for longevity. This would make it a tool worthy to compare to any quality tool. That being said, the design of this jig is superior to any I have personally seen so far. I have had no problems and I recommend this jig to anyone wanting to mill out 80% receivers.

  33. A Product that makes you a Machinest

    Posted by Unknown on 23rd Jan 2015

    A product that requires more time between transitions. This however keeps you from rushing. I recommend a drill press, you will increase the life of the product. Use lots of lubrication on the smooth shank of the cutter as well. If you don't you could score the jig from the friction build up and lessen the life of the jig.

  34. Quality throughout. Best buy.

    Posted by Robert on 20th Jan 2015

    Just pick up this jig and you immediately notice the quality construction. Attach it to a lower and it just works. Rock solid attachment.

  35. Truly Universal

    Posted by Devil Dog. on 11th Jan 2015

    This is a truly universal jig. After some time reviewing a couple options I decided on this one. This is the most effective jig on the market at this time. Looking forward to completing my first lower soon.

  36. Great Product

    Posted by Big Ern on 11th Jan 2015

    As an Engineer I think this is the best 80% jig on the market. I looked around for weeks before I decided to buy one. If you spend some time researching jigs you will come to the same conclusion.

  37. great

    Posted by Unknown on 9th Jan 2015

    Fits perfectly and was a piece of cake compared to the drill press jig I have.

  38. Easy to use and Best UNIVERSAL jig on the market!!

    Posted by joseph on 9th Jan 2015

    This is one the easiest and user friendly jig on the market. Finished a few lowers with the extended finger guard and it worked perfectly. Just take your time and frequently clean in between each mill step (a little OCD) but the finish turned out great. Finished lower had straight and even cuts and the within spec.

  39. Best Jig on the Market...

    Posted by Glen Barnhardt on 2nd Jan 2015

    I spent a lot of time looking for a jig that didn't require a drill press or mill to complete the lower. Yesterday (Jan. 1, 2015) I completed my lower. It worked perfectly. It took about 4 hours just to complete the milling but it came out looking like a professional did it. If you have a drillpress it would be much easier. You have to exert quite a bit of pressure to drill the holes. The routing was a breeze.

  40. Good looking end product

    Posted by Unknown on 26th Dec 2014

    I have done 4 cerro castings using this jig. The routing is a bit time consuming but the end product has good tolerances performed flawlessly at the range.

  41. Awesome!

    Posted by Robert on 6th Dec 2014

    I got this jig since it seems to be the best at being able to accept all kinds of lowers. I love the red color and how the side plates can be used on either side. Just make sure you read the instructions and take your time.

  42. Awesome Jig!

    Posted by James on 29th Nov 2014

    I love this thing! I have another Jig that I bought from 80% arms that uses a drill press and this thing makes it a lot easier. Love using the router. Genius!

  43. modulus jig

    Posted by Unknown on 11th Nov 2014

    This jig is great, easy to use. Looks like it will hold up for several lowers, I already did one the day I received it and it took around 3 hours from start to finish.

  44. exercising your rights just got easier

    Posted by JR on 22nd Oct 2014

    I wish this jig came out sooner! I was working on a lower I had when I saw this. Suffice to say I completed the work in progress with this jig and then completed another lower as well in less time it took me to complete 50% of the first lower (used drill press milling method). Definitely an excellent buy.

  45. Good Product

    Posted by Unknown on 16th Oct 2014

    The product is genius, a jig that is universal and uses the take down pin and the buffer as a guide for where the slots are to be drilled out. All the pieces fit well together, extremely easy to use, user friendly even for the first time users.
    Customer Service is great, i received my jig with slight damage, not necessarily their complete fault but i think packaging could be better in order to prevent the pieces damaging each other in the process of shipping. Overall, happy with the product and will order another one just to have a backup

  46. Finished my lower!

    Posted by Bob Taylor on 8th Oct 2014

    I recently finished a Tactical Machining 80% lower using the Modulus Arms jig. it is the only one I found that is truly universal as it locates the lower from the buffer tube mount and the front pivot pin location.
    The finishing of the lower went well. I went slow. The process was easily controllable and I got an acceptable finish in the end. I found that I drilled the fire control pocket "just a bit deep" which left three small dimples in the floor. Not a big deal, but I would recommend drilling just a bit shy of where the depth gauge suggests and mill the rest of the way down.
    I have assembled the firearm and took it to the range yesterday. Operation was flawless.
    I would recommend this jig and I think I will do another lower in the very near future.

  47. So far so good

    Posted by Matt on 21st Sep 2014

    Very complete set of instructions, I printed them in color. I did nick the trigger hole while milling but that doesn't seem to have any negative impact. If so I'll buy another template when I try another lower.

  48. This is the best!

    Posted by GMG on 4th Sep 2014

    I love this the Jig and Fabrication Tool Kit. It was easier than I thought it would be. Customer service was A++. Thanks, Modulus Arms.