MASTERPIECE ARMS MPA57 SST 5.7X28MM

Revamped and revitalized, MasterPiece Arms takes a crack at the…

Revamped and revitalized, MasterPiece Arms takes a crack at the MAC platform with its MPA57 SST—shown here with an Aimpoint Micro T-1 2MOA Red Dot sight.

I remember my first contact with an RPB MAC-10. It was produced shortly before they were forced to redesign it to fire from a closed-bolt.

Despite what many think, open-bolts have several negatives. The first, according to several sources, is that the firearm can be converted to full-auto more easily, which is something Uncle Sam doesn’t like too much. Another problem is accuracy is compromised when a massive bolt slams forward each time you pull the trigger, driving the muzzle off target—not that anyone ever thought the MACs were going to win an accuracy competition. With less than stellar accuracy, after I got past the ‘cool’ appearance, I decided the MAC open bolt models were “ho-hum” handguns. A decade later I had several opportunities to work with a suppressed, full-auto, open-bolt MAC,
and discovered what the mystique of the MAC-10 was all about! It still was lacking in the ac-curacy department, but could it shoot. After a few more closed-bolt MACs passed through my hands, I decided semi-auto closed-bolt models were capable of decent accu-racy and seemed more fun to work with than open bolt models.

I suppose others felt the same attraction, because after RPB closed their doors several folks tried unsuccessfully to make a go of offering their “MAC-10s.” Then in 1992 MasterPiece Arms sprang into being. Well, not really “sprang,” con-sidering Gary Poole, MPA’s founder, was a machinist whose shop had manufactured parts for RPB and their successor SWD. This definitely gave him a leg up when it came to re-establishing MAC pistols.

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The 5.7x28mm round is high in velocity but low in recoil, mitigating some concerns with the platform.

MPA’s goal was to improve the pistols (and car-bines) using modern manufacturing technology such
as CNC lasers, lathes and machining centers as well as extensive quality control for the parts production, while maintaining the blowback system. Design improvements of the bolt and extractor were incorporated, along with the option of a side or top cocking handle model.

In 2008, Poole sold the company but remains active in it. Their Protector series contains their new .380 subcompact pocket guns and new pistol, the MAC-like MPA57 SST (SST stands for Side cocker, Scope mount, Threaded barrel), chambered solely for 5.7x28mm.

The 5.7x28mm round was designed in the early 1990s for use by military and LEOs in a Personal Defense Weapon (PDW). Its main traits are low recoil, high velocity, and penetrating body armor with the right bullet. Eventually, with the advent of commercial ammuni-tion loaded with bullets appropriate for recreational use, and no fear of armor penetration, the round found its way into the general public, chambered in a few firearms, including at least one pistol.

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A 3-inch long muzzle break is integral to the barrel, easing the impact of the weapon’s recoil.

Load Comments
  • JH

    Low recoil round, but they have to stick a long tacky looking muzzle break on there…