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Thread: Picatinny and weaver rails and mounts and utter confusion!

  1. #1

    Picatinny and weaver rails and mounts and utter confusion!

    Any help/tips to solve this one would be much appreciated:

    I am trying to mount a Burris Fastfire 11 on a Mossberg 500 P/A 20G shotgun.
    The Burris Fastfire 11 came with an optional Picatinny Protector Mount. See
    I have fitted the Fastfire 11 to the Protector Mount.
    This Protector Mount 'fits all Weaver-style and Picatinny-style bases', anyway that is what it says in the brochure...
    The shotgun action is drilled and tapped and fitted with a Weaver Rail.

    So it should be easy to fit the Picatinny Mount to the Weaver rail, however this it where things go wrong as it doesn't fit.
    The Picatinny Mount has a round screw type fitting with a nut from left to right but the Weaver mount has square cut outs. Now, a round thing never fits nicely into a squire and anyway the diameter of the round bar (with screw on the end) is larger than the diameter of the square cut-outs on the Weaver base.

    Could anyone please enlighten me....? Thank you very much!
    and BTW my retailer who sold me the various bits has gone out of business since the purchase.

  2. #2
    Picatinny Rails, Weaver Rails, What’s The Difference?
    By Andrew Swan

    The “Picatinny Rail” is a term that has evolved in the firearm industry from a military standard, specifically MIL-STD-1913 (AR) which was adopted on February 3, 1995. The title of the publication is “Dimensioning Of Accessory Mounting Rail For Small Arms Weapons” and this document specified exactly what the dimensions and tolerances were for any mounting systems that were to be submitted for acceptance by the military. The term “Picatinny” comes from the place of origin for this system, the Picatinny Arsenal located in New Jersey. MIL-STD-1913 specifies the dimensions required for consideration, including length, width, height, and angles and the tolerances allowed for each measurement. The key distinction of the MIL-STD-1913 lies in the specification for the profile and the recoil groove.
    Click image for larger version. 

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    Source: MIL-STD-1913 (AR) 3 February 1995

    Click image for larger version. 

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    Source: MIL-STD-1913 (AR) 3 February 1995

    What are the differences between the “Picatinny” and the “Weaver” systems? The profile of the two systems is virtually identical. Depending on the quality of the machining done by the manufacturer, the two systems should be indistinguishable from the profile. The key difference lies in the placement of the recoil grooves and with width of the grooves. MIL-STD-1913 (Picatinny) grooves are .206” wide and have a center-to-center width of .394”. The placement of these grooves has to be consistent in order for it to be a true “Picatinny” MIL-STD system. Weaver systems have a .180” width of recoil groove and are not necessarily consistent in a center-to-center measurement from one groove to the next. In many instances, a Weaver system has a specific application that it is machined for, so interchangeability is not necessarily an issue. A MIL-STD-1913 system must adhere to the specifications listed above in order for it to be considered MIL-STD, since the military desires uniformity in the recoil grooves to allow for different systems to be mounted on the weapon with no concern for compatibility.

    Now, what does this mean to you? Boiled down, it means that accessories designed for a Weaver system will, in most cases, fit on a “Picatinny” system. The reverse, however, is probably not the case. Due to the larger recoil groove, “Picatinny” accessories will not fit a Weaver system. There are, of course, exceptions to every rule, but for a good rule-of-thumb, “Picatinny” won’t fit Weaver, but Weaver will fit “Picatinny”.

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