Kramer Defense Files Patent for Bolt Heads for Cartridges Larger Than 6.8mm SPC, Wildcat World Reacts

    Kramer Defense, the company that introduced the 6.8x45mm UCC cartridge based on the .378″/9.6mm diameter case head of 5.56mm, filed a patent on Aug 14, 2014 (approved Sept. 1, 2015) that has recently sent shockwaves through the 6.5 Grendel and cartridge wildcatting communities. The patent relates to bolts of larger diameter than the standard AR-15 bolt, coupled with cartridges of larger size and bore diameter. The most relevant section of the patent is below:

    The invention claimed is:

    1. A kit for modifying an M16 rifle, M4 carbine, or AR15 rifle or carbine, comprising:

    a bolt having a maximum outside diameter (K in FIG. 3C) greater than that of a standard M16/M4 bolt (existing M16A1-A4 versions and M4 and M4A1 versions);

    an ejector carried by the bolt;

    a bolt extractor pivoted to the bolt and having a maximum width (F in FIG. 4D) greater than that of a standard M16/M4 bolt extractor (existing M16A1-A4 versions and M4 and M4A1 versions),


    the bolt, the ejector, and the bolt extractor operable to:
    transport a cartridge from a magazine to a barrel, and

    eject a spent cartridge from the barrel,

    a length of the cartridge is equal to or slightly less than 2.26 inches, and

    the cartridge comprises:

    a case having a case head diameter greater than 0.378 inch; and

    a bullet having a diameter greater than or equal to 0.224 inch; and

    a barrel extension configured to receive the bolt.

    Because of these claims, many AR cartridge enthusiasts have become upset, with some even forming a Facebook group “Boycott Kramer Defense”, as the patent outlines a set of features that have long been the purview of wildcatters and others trying to push the capabilities of the AR-15 rifle. One example of this being Olympic Arms:


    TFB asked Olympic Arms about this patent, and they said: “[Grendel / WSSM rifles] has been on the market since 2004, and first cataloged in 2005. Our Grendel bolts and extensions have been sold openly since at least 2010.”

    Overreaching patents are nothing new; perhaps the most well-known example being the infamous “stick” patent of 1999, but a more recent and relevant patent of questionable scope being the Liberty Ammunition three-piece bullet patent that led to a court case with the US Army regarding their M855A1 round. Whether the Kramer Defense patent is an example of an invalid patent or not is uncertain, but certainly some of the features it covers are replete with examples of prior art.

    On the Boycott Kramer Defense page, patent attorney Ben Langlotz explains a little more about the patent’s scope:


    While this doesn’t necessarily mean Kramer’s patent is enforceable, it does exclude from the patent’s scope existing 6.5 Grendel rifles using bolts of standard outer diameter, as well as the Remington .30 RAR R-15, as it uses a different upper receiver forging.

    Nathaniel F

    Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. He can be reached via email at [email protected]