Windham Weaponry MCS Multi-Caliber Uppers

Kit MCS2

Windham Weaponry announced new uppers that allow the shooter to quickly change calibers from 5.56 NATO to either 300 BLK or 7.62×39. The uppers are called MCS, or Multi-Caliber System. Currently, two are being produced: MCS1 and MCS2.

The MCS1 has a complete 5.56 NATO upper assembly, and comes with a swappable barrel for the 300 BLK. The MCS2 has a complete 5.56 NATO upper and 7.62×39 quick change barrel, plus a bolt carrier group and magazine for the Russian cartridge.

Readers may notice that the forend retaining system looks similar to the system used by MGI on the Hydra line of rifles. I exchanged e-mails with a Windham Weaponry representative about the new uppers. He confirmed that the Multi-Caliber System uses technology licensed from MGI, and that the two companies have had a long-standing association.

The MCS1 has a suggested retail of $899, while the MCS2 has a suggested retail of $999.

Richard Johnson

An advocate of gun proliferation zones, Richard is a long time shooter, former cop and internet entrepreneur. Among the many places he calls home is


  • hking

    Woah that looks ugly as all hell. I cant say I have ever needed to change a barrel out in such a way. If I am going to have multiple calibers for one lower, I will just get an entire upper.

    • Its for people that want an AR15 that would also fire AK rounds but don’t want to buy an AK rifle.

  • Grindstone50k

    For those prices I could build all three calibers in separate uppers plus the lower to match.

    • Cal S.

      Shhh… You’re just supposed to pay what they ask for without question.

    • JSmath

      Aw, poop. I thought the prices listed were for whole rifles, I was super excited until I saw they were just the uppers.

  • kregano

    Man, I could just buy an entire AR-15 and a spare upper or barrel for .300 Blackout at the price for this one upper.

  • The Hydra uppers are pretty neat, it’s their lowers I am skeptical about.

  • The relationship between MGI and Windham tracks back to the old Gwinn Bushmaster Arm Pistol.

  • Sledgecrowbar

    This is a good step towards making the AR, which isn’t going anywhere, into a firearm that features all the things its would-be replacements have to offer. I’m still hoping for a free float rail that basically does this, but an upper/rail unit is also good because it isn’t necessarily limited by the standard barrel extension sleeve on the upper. Ideally, there would be a barrel nut that does this, and free-float rails of current design would be able to mount to it.

  • Nathan Means

    Operator tested, prepper approved

  • supergun

    Can you operate 7.62×39 on an AR 15 lower?