MasterPiece Arms' new 5.7x28mm SBR

MasterPiece Arms (MPA) is now producing a FN 5.7x28mm short-barreled rifle with a folding wire stock. This gun expands on their line of Defenders chambered in 5.7x28mm, which offer shooters some options that are markedly different than FN’s Five-seveN and PS90. Called the MPA57SST-SBR, this follows their carbines and pistol also chambered for the exotic cartridge.

The MPA Defenders are based on the Military Armament Corporation’s M-10, aka the MAC-10. They have been updated with a side charging handle, a top rail for optics and have a quad-railed forearm for accessories. The MPA57SST-SBR comes with a Cobra grip by Strike Industries, a angled foregrip with a hand stop that also acts as a standoff device for shooting from cover.

MPA57SST-SBR with 5.56 silencerLike the other Defenders chambered in 5.7x28mm, the pistol grip has been modified to accept standard Five-seveN magazines, which are available in 10-, 20- and 30-round capacities, and comes with one 20-rounder from the factory.

We like the addition of the slender folding wire stock over the carbine’s AR-style fixed tube stock. It can be fired with the stock folded. We also like that they’re manufacturing NFA-regulated guns from the factory, no gunsmithing needed.

The MPA57SST-SBR is a Title II firearm, meaning you have to have a tax stamp and jump through other hoops to get it. It is designed to accept suppressors as well, and the 8-inch barrel is threaded 1/2×28. MasterPiece Arms has developed a silencer for 5.56 that is compatible with this SBR, but it is not currently available.

It makes a lot of sense to use an SBR with 5.7x28mm. The cartridge was designed for the P90 submachine gun, and it loses a lot of muzzle velocity from the cut-down barrel of the Five-seveN, undermining the cartridge’s effectiveness.

And when ammo can cost you a dollar or more per round, it should also be said that the MPA57SST-SBR retails for $800, which is considerably less than a Five-seveN or PS90.

But we do have to wonder why their first SBR is chambered for FN 5.7x28mm. They also make carbines in 9mm and .45 ACP, both of which also benefit significantly in the ballistics department from longer barrels, not to mention score higher marks in availability, price and ultimately energy.

Still, this looks like a fun range toy and we hope it means that MasterPiece Arms is working on future SBRs chambered in more accessible calibers. But if they’re dedicated to the exotic stuff, can we get a .460 Rowland again?

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