Announcement of the 400AR was first posted on March 9, 2016. For the latest discussion, check out the article at The Firearm Blog: http://www.thefirearmblog.com/blog/2017/06/08/400ar-another-wildcat-cartridge-ar-15/


12 thoughts on “400AR

      1. If you’re married to the Russian case, you might look into the 9×39.
        The 7.62×39 was dismissed early on in the development of the 400AR, because it is too tapered at the web and too short for maximum powder capacity. The 400AR produces the most muzzle power possible from a double-stack AR-15 cartridge.


  1. It would be interesting to see how the 10 Auto 115grs Extreme Defender bullet from Lehigh would perform loaded in the 400AR.
    It’s solid, rated for velocities up to 4k fps, so that should not be an issue.


  2. Is it possible to purchase an upper and BCG or possibly send a barrel and have it reamed?
    I am very eager to get my hands on this caliber and put it through the paces hunting.


  3. Lehigh defense has also made a 10mm bullet (.400) xtreme penetrator for muzzleloader as well that weighs in a 200 grains ! I was planning on ordering a box next time and seeing what ,if anything it would do in my 10mm. It’s be badass if this new at also accepted 10mm & 10mm magnum rounds ! Does this new round headspace on the shoulder or is it a rimmed cartridge ? Looking forward to my next build. Was gonna do a 458 socom but may just throw my hat in the ring for the .400 ! Will the ejection port need to be opened up ,how bout ballistics, barrel length & gas system ? Man I got questions for days…


    1. The above article reads, “maximum allowable chamber pressure of the proposed AR wildcat would be around 50,000 PSI” which became the 400AR standard. Specific loads are undisclosed.


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