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The Bushmaster Unicorn, Also Known as ACR Caliber Conversions

Do They Really Exist?


Huntsville, AL – The Bushmaster ACR was brought to market in 2010 with the promise of unparalleled adaptability.  The concept was simple; an extremely reliable, versatile, and modular platform, capable of tool-less configuration and caliber changes in minutes by swapping the bolt head, barrel and magazine.  Unfortunately, much like a mythical creature, the caliber conversions have never been seen.  Until now.


Finally, after many years of development, we are excited to announce the first of many new caliber conversions for the ACR. With fully ambidextrous controls, improved ergonomics, an ultra reliable gas piston operating system, and tool-less configuration and caliber adaptability, the ACR is now the most field adaptable Modern Sporting Rifle Platform available.


.450 Bushmaster Conversion

Ultimate stopping power for deer, bear or feral hogs


6.8 Rem SPC II

For increased energy and down-range performance


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31 Responses to “The Bushmaster Unicorn, Also Known as ACR Caliber Conversions”

  1. Jack says:

    8 years to get .450 and 6.8….. 6.8 was exciting in 2010. Not so much now. 762×39, 300blk, 6.5, I’d even be interested in some 5.45 just for kicks.

    • Matthew says:

      If you want 7.62×39, .300 BLK, 6.5 Grendel or others for your ACR, then get them! Third parties have been making them for years!

      • Jack says:

        I’m long past investing in an ACR. I’ve got an XCR in all the calibers I’ve mentioned and enjoy it immensely. My googlefu must be weak because a quick search of “acr caliber conversions” doesn’t get me much. Out of academic interest I’d love to know who’s offering and what the availability/cost/performance of those Third Party offerings are.

        • Stephen says:

          Dana Beck over at Templar Precision offers caliber conversions. Can find him on the ACR Forum and group on FB. You can tweak most things on the platform actually and aftermarket support from major players is coming along nowadays

    • Dave says:

      My thoughts exactly. This is worse than the auto industry. .300blk is a no brainer. 6.8SPC is a commercial failure. WTF, Bushmaster.

    • Ken says:

      Ummmm, you missed the whole U.S. Army moving to 6.8 SPC, huh?

      • Jack says:

        6.8mm for their new SAW. Not 6.8spc. the below is quoted from a post on this blog from the 4th.

        This is not the 6.8 SPC cartridge evaluated by SOCOM in the mid-00s and available commercially. The only thing this has in common, is caliber.

  2. Stash says:

    Similar thoughts – I bought one in 2010 fully expecting to upgrade with new barrels and calibers over time. I have an enhanced and the only factory mod I bought for it was the plastic handguard from the basic version.

    Definitely interested in .300blk, 7.62×39, and 5.45 kits if those are in the works. Plus the handguards that have been showcased at SHOT over the years by Remington but not released for commercial purchase.

  3. BatBoy375 says:

    I’d be more interested to see the lowers they promised to accept AK pattern mags.

    • Matthew says:

      They NEVER promised that!

      • Stash says:

        Bushmaster didn’t but it was a part of the original Masada design. Being that the upper is what is serialized, and the lower being polymer anyway, it “shouldn’t” be an un-achievable engineering/design/production feat.

        Not holding my breath though. 8ish years to get a factory caliber conversion kit doesn’t point to cool stuff like that happening.

  4. JMAA says:

    They still have a bit of a following up here in Canada due to their non-restricted firearm status, so maybe in a year or three these calibre kits will arrive here, heh.

  5. Is the 6.8 SPC the same as the 6.8 the Army is talking about for their Next Gen SAW?

  6. Mike says:

    Sounds like they’re just clearing inventory of old barrels in calibers nobody shoots. They aren’t offering anything anyone wants.

  7. Alpha2 says:

    Why 6.8spc? Thought that was pretty much a failure and dead.

  8. CAP says:

    So for a couple hundred dollars more than a complete upper receiver assmbly for an AR15, you can get a new barrel for an ACR?

  9. jellydonut says:

    2007 called, it wants its rifle and its calibers back.

    .450 Bushmaster is actually pretty cool, though.

    But really, the piston cult is an artifact of history. DI is lighter and more accurate. Stick to DI.

  10. Alex says:

    Looks like they have a 10.5″ pistol and factory SBR on the site as well.

    One thing I appreciate about the ACR is the 7075 upper. Probably could’ve extruded it from 6061 or 6063 like other competing designs but it’s a welcome spec.

    Also that graphic… accurate.

  11. Sgt A says:

    Jack totally nailed it – it’s 2018, and I can finally convert that setup to calibers I no longer have any interest in.

    Man, I’d have dumped so much money if the original Masada existed as a thing, and been thrilled about it… so much money left on the table due to the ineptitude at Bushy/Rem in actually getting that to market.

    • Jack says:

      It’s got a ton of bad internet mojo but my XCR since 2009 has offered all the calibers I mentioned and then some. It takes a leap of faith but mine have been well worth it.

  12. charlie says:

    No 300BLK?

  13. Mike says:

    Bushmaster continues with their stellar failure to grasp what the market wants. Are they trying to fail on purpose, are they actually that stupid or inept? The whole ACR world waits breathlessly for .300, 5.45, 7.62×39…….NPOE here’s the 6.8 and 450 NOBODY wants. IDIOTS!

  14. royceda59 says:

    One word explains everything – Remington

  15. Brad says:

    When will this be available

  16. kyle kata says:

    Bushmaster showing that they still have it*.

  17. Jon, OPT says:

    They offer these calibers? In that case why not add a .50 caliber musket ball, black powder, muzzleloader? I mean, if you’re going to dial it back, freaking dial it back.

  18. Joe says:

    This would have been cool in 2010.

    But I can build an acceptable 5.56, .450 and 6.8 AR together for the base cost of an ACR, and nice ones if you factor in the caliber conversion cost.