Are machine pistols all that useful? No. Do I love them? Yes. Yes, I do. The closest thing to a machine pistol I’ve ever shot was a MAC-10, and many may argue that that doesn’t count and it’s an SMG. Regardless, guns like the Beretta 93R and Glock 18 have always captivated me, especially the 93R. One I only recently stumbled into was the Robinson SR-11.
The Robinson SR-11 never entered full production and only made it through various prototype stages. While it’s a machine pistol, it’s unlike any other machine pistol ever created, which is why it may have never gotten popular. The design seems ingenious, and what we know about testing seems to say it performed well.
We can’t grab one and try it, but we can at the very least examine the design and discuss what makes it seem so damn cool.
A World War 2 Machine Pistol
If you’re a fan of weird firearms, you’ve likely heard the name Russel Robinson. Russel Robinson is mostly known for his work with constant recoil machine guns, which are so dang cool. The SR-11 isn’t a constant recoil machine pistol, but it’s almost a constant recoil design.
Robinson was an Australian, and the Australian Army Inventions Directorate directed him to produce a 9mm version of another machine pistol called the Gatenby gun, which was a .45 ACP pistol. Robinson began knocking out various prototypes, and eventually, in 1944, he had the SR-11. The SR-11 was subject to numerous small changes and improvements throughout its lifespan.
The first prototyped SR-11 was produced in 1945. In 1946, he took the gun to the United Kingdom’s Ordnance Board. This is where we see a little data from the gun’s testing. Small Arms Review is our only source of real information about this firearm.
The testing showed that the Robinson SR-11 was more accurate than the STEN Mk V in automatic fire but less accurate in semi-auto. I know what you’re thinking. How does a machine pistol perform better in full auto than a dedicated submachine gun? That’s a matter of design.
The SR-11 – What’s Different
Machine pistols are well known for being difficult to control. They often require some form of stock to work correctly, and the SR-11 had a stock. Kind of. There was an option for a detachable tubular stock that attached to the rear tang of the pistol. We didn’t have much of a stock, but it was better than nothing.
The SR-11 used a straight blowback system, but also used an open slide design. The open slide design is essentially an open bolt design on an automatic pistol. The only other notable open slide design I’m aware of is the PM-63 RAK. I imagine the slide being fired from the open position didn’t help with semi-auto accuracy. The slide slamming forward when the trigger is pulled might cause some accuracy issues.
Another weird design feature is the helical floating barrel. Robinson took some influence from his constant recoil designs. When you pressed the trigger and the slide slammed forward, the helical barrel portions engaged with helical cuts in the slide. This helps reduce recoil, as does a slight bit of additional movement after the gun fires. The barrel and slide reportedly move forward just slightly.
After the gun fires, the slide shoots rearward and stops, which is why it’s not a true constant recoil design. This semi-constant recoil design explains why the gun had better automatic accuracy than the Sten, which I imagine was due to less felt recoil.
That’s Not All
Mr. Robinson wasn’t stopping at an odd operating system. The SR-11 would also automatically eject spent magazines, and when reloaded with a fresh magazine, the slide would automatically cock to the locked position. Those magazines held 14 rounds, an impressive amount for the era.
The gun’s firing rate hovered around 600 rounds per minute. That’s fairly controllable and likely another benefit of the semi-constant recoil design. Sadly, the SR-11 might have gone through several incarnations and experimented with everything from different metals to heavier slides, but it never escaped the prototype stage.
Where would a machine pistol ever fit in a modern military or police force? That’s tough to say. We haven’t really seen any machine pistols ever succeed in a serious role. Still, the SR-11 had some interesting ideas, and it’s one of those many guns we’ll never get our hands on.
