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Milling picatinny rail advice?

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  • Milling picatinny rail advice?

    Hello, all!
    I'm considering milling some picatinny rails for an AR I've decided to build and was wondering if any of you fine folks may have some advice to offer... the old "Maaaaan, if I had only known that when I started..." scenario.
    Anyone ever done any of these?
    Here are some specs for those who are curious but unfamiliar...

  • #2
    I made something similar. I had a Panda action that has a 60* "male" dovetail rib on the top, and I wanted a tapered base for long range shooting. Burris makes a good set of scope rings that has inserts that come in various thicknesses and can handle raising the scope properly, but they only come in a "Weaver" style attachement. So, I made a dovetail to Weaver rail, and it came out great!

    I used aluminum, cut the dovetail first, I hogged out the center of the dovetail with an endmill, then you have to run the dovetail cutter in one pass. I kept coolant going and kept the swarf blown clear, no problems.

    Then the top I used 45* mills, and used a couple Weaver bases I had to pull dimensions from. It came out good. It was easier to do than the dovetail I think, but it takes more passes. I did not make all the slot cuts like a picitiny has, I only made the slots I needed, but the concept is the same.


    • #3
      If you're can get by with steel, you can buy some short lengths of Weaver stock from Brownells - the only difference between weaver and Picatinny rails is the cross slot sizes and spacing.

      EGO partum , proinde EGO sum


      • #4
        Thank you for posting--that goes into the old notebook for future reference.

        Now pardon my ignorance, but why are they called "Picatinny" rails?



        PS Looks painful to make without CNC. I would think maybe a form milling cutter is in order to do the rail sides. If you made one up (or heck, maybe someone sells one), you could do each side in one pass. Or, maybe just use a form to cut the 45's, and then a regular end mill to cut the rectangular portions, so a couple of passes on the sides. Then you cut the horizontal grooves one at a time.
        Try G-Wizard Machinist's Calculator for free:


        • #5
          They're called "Picatinny rails" because Picatinny Arsenal came up with the mounting specification.Technically, they're proper designation is MIL-STD-1913, and they're NATO designation is STANAG 2324

          And oh, EGW sells it in "blank" form for custom Applications.

          Last edited by HTRN; 03-06-2007, 12:26 PM.
          EGO partum , proinde EGO sum


          • #6
            The thought that comes to mind is the multipurpose mill/drill/countersink tools advertised at enco and probly others the ends are 45 degrees.
            Looks like a good shaper project depending on length.

            Bob: These were apparently developed at Picatinny Arsenal. (I googled) Some good things do come from New Jersey.
            Ad maiorem dei gloriam - Ad vitam paramus


            • #7
              Painful, yes... I agree. particularly the top grooves. The spec says .208 and of course common endmill sizes aren't right on... Enco and McMaster carry endmills in 64ths which leaves me with .1875 (3/16) followed by .2031 (13/64). RWS brings up a good point of only milling the grooves where they're needed. that would save a bunch of time and if I'm not having it annodized I could always add more grooves as the need arises.

              I had the same thoughts about countersinks from Enco. They have reasonably priced (import) 45 degree countersinks and dovetail cutters that would work nicely. I'll be using 6061, so I even have a couple carbide 45 degree 1/2" shank router bits that would probably work as well.

              However, EGW's prices are pretty appealing... Without CNC it looks like this would take quite a while. It doesn't seem too difficult, just tedious. Ah, I dunno... I don't mind busy work, but maybe my time would be better spent on other parts of the project.


              • #8
                I found out about the groove spacing a couple of weeks ago. I wanted to make a 1" tall extended rail with grooves to fit like teeth onto the flattop upper grooves. After finding out about what a pain it would be to make the grooves I decided to buy one.

                I'm building a varmit upper at this time. Got a little more meat to take off the 1n12 tube. I machined out for and installed roller bearings in my steady rest, should have done that long ago.



                • #9
                  Originally posted by Magee
                  I'll be using 6061....
                  Magee. I do a lot of custom work on AR's. I have also machined A LOT of 1913 rails. I would strongly suggest using 7075 instead of the 6061, especially since you won't be hard anodizing it. The 6061 is really soft and it will show every ding and light scratch. 7075 isn't as gummy to machine and it is much tougher in strength and surface hardness.
                  I suggest high speed, medium feed on the cuts with a 3 flute non-centercutting TiC or TiN or TiCN or TAlN coated endmill for the finish cuts.
                  Considering the price of all of the rails available for AR's, it almost isn't worth your time to make the rails unless you just want to make something.
                  Custom work in the Republik of Kalifornia is tuff considering citizens can't buy them anymore in this state.
                  Most of my customers are law enforcement and government. Although many of the citizen customers bought several lower receivers before the 1989 ban, and I build many crazy upper recievers in many different calibers, particularly off of the AR-10 platform.
                  I have (2) AR-15's and (2) AR-10 lower receivers + many upper receivers.
                  Anywhere from 16" barrelled AR-10's in .308 for 'Hog Hunting' to .300 Remington Short Action Ultra Magnums for long range. I am currently in the experimental phase of making a .338 out of a necked up .300 RSAUM case, and a .450 Marlin Big Bore for bear and other large critters. I rifle my own barrels and do my own reaming so I can make whatever I want.
                  If you haven't already done so, go to
                  They have a wealth of info on that board. Your wallet will feel a sucking sensation when you see other members' rigs. My screen name is WARDOG7366. If you have a hankering, can you post a pic of the AR you are runnin'?
                  Duke Reno / Yankee Metallic Metalcraft


                  • #10
                    Thanks for the advice, Duke.
                    I hear you on the 7075. I just have a ton of 6061 kicking around. Maybe I'll see if the local non-ferrous guy has any 7075. He sells 6061 drops for $1.50 a pound, but I've never seen any 7075 in the cheap-bastard pile. It's worth another trip to find some if I'm gonna spend all that time machining a rail or four. You're right, though... after I buy the 7075, it's hard to justify making them myself as far as cost is concerned, but ARs are kind of like hot-rods... nobody wants a stock rig and none of the guys I see at the range have anything you can't just order from Midway or Bravo Company.

                    The rifle is a ways from being done, but I'm trying to make it kind of like a Sport Utility Rifle... Something that does a little better over longer distances, but doesn't sacrifice maneuverability... not sure how well it's gonna work out, but I'm setting it up with a 16" free-floated bull barrel. I do some lurking over at and those guys have had real good results making 20" bull-barrelled .308's into sub-MOA rifles. That was shorter than I expected when I first read about it, but the logic seemed solid. Time will tell if it works for my AR, but I figured I'd give it a shot.


                    • #11
                      Originally posted by HTRN
                      They're called "Picatinny rails" because Picatinny Arsenal came up with the mounting specification.Technically, they're proper designation is MIL-STD-1913, and they're NATO designation is STANAG 2324
                      Actually they were conceived and designed by Knight's Armament in FL. Reed Knight approached Picatinny with the prototype design to see if there was interest for this new and radical mounting method. Picatinny took the rail system and used the prototypes to write the specifications. Once they were adopted by the US Army, Picatinny "conveniently" forgot where the prototypes came from and called them "theirs."


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