Violations of the Picatinny rail Mil-STD 1913

Håkan Spuhr, owner of Spuhr shared this on Facebook and Instagram and it’s worth considering:

“Top is NATO drawing of Stanag 4694, the back compatible replacement for Picatinny Mil-std 1913.
Lower is one “so called picatinny” and there is a lot of those violations of standard out there.
To put it simple, cross slots should be minimum 5.23mm and square in bottom and there should be 10mm C-C betwen them.
If there not is that, it’s not a Picatinny, and not a NATO rail either!
And it does matter if God’s own Armoury have produced the rail, it’s simply wrong!



Picatinny Rail – Standard versus Reality.

For more information and facts, check out Wikipedia on the Picatinny Rail.

For instance, did you know this? “The rail is named after the Picatinny Arsenal in New Jersey, USA. The Picatinny Arsenal’s role with the rail was to test/evaluate it and to create a military standard for it. This was Mil-STD-1913, dated February 3, 1995

And the NATO Accessory Rail STANAG 4694.

“According to the NATO Army Armaments Group the differences between the MIL-STD 1913 Picatinny rail and the STANAG 4694 are:

  • A metric reference drawing.
  • Additional new measurements and tolerances.
  • Adjustments of some measurements.
  • Reduction of straightness tolerances with approximately 50%.”

Below: Håkan Spuhr at IWA in Germany 2016.

Håkan Spuhr

The obvious questions is – what violations are out there? Which are the worst?

Eric B

Ex-Arctic Ranger. Competitive practical shooter and hunter with an European focus. Always ready to increase my collection of modern semi-automatic firearms, optics and sound suppressors. Owning the night would be nice too.


  • Evil13RT

    So I’m a total noob to this but… For what purpose do multiple standards exist?
    One seems sufficient to my limited understanding of attachments.

    • bert

      One would be… but when one nation in an alliance uses imperial measurements most of the time, while the others use metric, there will be difficulties.

    • randomswede

      First see the xkcd comic included.
      Second there are only two _standards_ for what we are used to seeing in modern times MIL-STD-1913 Picatinny made a military standard in 1995 and the backwards compatible STANAG 4694 made a standard in 2009. Anything outside that is either not up to the standard or a proprietary system.

  • I’m guessing they are relaxing the straightness tolerance so less extruded rail sections are rejected. Also according to wiki entry the gripping surfaces are different between the standards which can be significant. There is another rail standard that you did not mention and its the Canadian one that predated the Picatinny and uses slightly different numbers.

    • marine6680

      A reduction in the tolerance could mean they tightened the tolerances.

      Need a bit more context than the one quote in the article.

  • Mmmtacos

    What violators are out there? The ones that still insist on using Universal rails instead. I’m looking at you, Glock.

    • Joseph Smith

      And Sig.

    • Well if you look at the standard, according to wiki, the entire top ie flat surface of the rail is now considered an indexing spot for mounting so any rail that is milled down the middle like the ones in the pictures above would violate the STANAG rail standard.

      What is weird, according to wiki,

      is this statement and testing seem to contradict itself.

      “Another notable change is the recommendation that while in the Picatinny
      rail system the V-angles are used for the alignment and reference of
      the accessory, NATO recommends using the top surface instead.

      NATO tests have shown that the Picatinny rail system does not provide good repeatability. Using the top surface as a reference and alignment of the grabbers provided excellent repeatability.”

      So they tested the rails and determined that the flat does not repeat index well and then go on to state that the flat is now a key index point? Crap like this is why governments fail when it comes to design and engineering, as well as numerous other things like education.

      • Mmmtacos

        They are treating them as two different standards.

        While the Picatinny (MIL-STD 1913) and NATO (STANAG 4694) should be the same the Picatinny system recommends that the index point of the system should be the V-angles, while NATO says it should be the top flat-surface.

        NATO isn’t contradicting itself, it’s saying the Picatinny system is flawed in that indexing off the V-angles (or, the sides, rather) proves poor to result in inconsistent rails from one manufacturer to another rather than the top.

        Also following NATO’s recommendation probably means you wouldn’t end up with anyone milling out the top, like you mention. I bet they do that to save weight.

    • Bill

      And SIG, except for the ones that aren’t wrong.

  • Sgt fish

    This has always bothered me and I will not buy from a company that claims to have picatinny rails when they mill out the center lugs. You sacrifice an extreme amount of strength by doing so and completely take it out of spec. You are essentially just putting in a flex point on the part that you mount your optic!

    • Otm Shooter

      It’s a common practice to extrude the rail with that center area removed, especially for overseas extruders shipping into the U.S. You buy extrusion and pay for shipping by the pound, not by the foot.

    • Michael R. Zupcak

      Do you mean the way SIG has “scalloped” the top rail of the Gen2 MPX?

  • Bill

    The goofiness involved in Pic Rail manufacturing makes me doubt more and more it’s viability for mounting optics. If a VFG, sling mount of light is a little off, no big deal, but that top rail has to be dead-bang on.

    • John

      The bottom also matters for grenade launchers. I suspect Russia concentrated on top and bottom rails for that reason in their newest designs.

  • Mrdakka

    Yay for GD&T!

  • John

    Here’s a simple test. Take a red dot and mount it on all rails. Then aim. If it’s straight on all of them, if it comes off easily, then it’s NATO standard.

    Also, Picantilly is inches. NATO is metric.