Heavy Metal: The Suomi KP/31

Ah, the sub-machine gun. Much like the drive-in movie theater, the pay phone, and the typewriter, sub-machine guns are a useful, if not revolutionary item whose time has passed. As I mentioned when I wrote about the PPS-43, they're more of a curio these days than anything else, but as a military history and firearms enthusiast, they continue to interest me. The 1930s and 40s were the heyday of the sub-gun. Every major power on the globe used them, and many smaller countries as well. And with good reason! Sub-guns bridged that gap between a battle rifle and a pistol, a gap that only someone who has worked in a military support or leadership role knows so well. For your consideration, I present one such gun that excelled in its niche: the Suomi-konepistooli 31 (Finland automatic pistol 31).*

A beautiful specimen with some honest wear. Note the figuring in the arctic birch stock.

Perhaps you remember Aimo Lahti, the famous self-taught Finnish firearms designer. No? Then go read about the pistol which bears his name.  One of Lahti's most prolific and successful designs was the KP/31 submachine gun. An early-ish sub-machine gun design that was developed during peace time, the KP/31 was somewhat of a labor of love. At the time, Finland's submachine gun was the foreign produced Bergmann. Lahti didn't think much of it. He wanted to develop a cheaper, more reliable weapon on his native soil. Lahti developed a prototype in 1922, but could not get state financing to proceed further. Collaborating with other Finnish Army officers, he raised capital and established his own private company, where work began in earnest. Their initial result was the KP/26, a rather odd looking gun with a highly curved magazine, and chambered in 7.65mm Luger. The Finnish Army wasn't much interested in submachine guns at the time, and the KP/26 was far from perfect, so the military procured only a few examples. As such, the KP/26 never really saw combat, and was relegated to Civil Guard and home defense roles.

The weird KP/26. You can see the influences this weapon had on the later KP/31.

This KP/26 had some reliability problems and was finicky about interchanging magazines between weapons, neither of which are characteristics that are desired in a firearm meant for military service. So, Lahti and team went back to the drawing board. They retained things that worked well (like the quick removable barrel) and eliminated those that didn't, including the curved magazine and odd stock. Internal enhancements to the bolt cured the reliability issues, and with a caliber change to 9mm Parabellum, the KP/31 was born. This time the military paid attention. Lahti sold the production rights for his new gun to the famed Tikkakoski company, and Finland had its first, viable, mass-produced submachine gun in 1931.

KP/31s being built at Tikkakoski. Note the barrel jackets still in the white. Photo courtesy of http://sa-kuva.fi/

The KP/31 was a blowback operated, open bolt, select-fire weapon with a non-reciprocating charging handle, and it was a built like a tank (perhaps from a tank?). Stamped sheet metal parts? Surely you jest. This thing was forged, and parts were milled out of solid steel. Even unstressed parts like the barrel jacket were machined. Topped off with a hardwood stock of arctic birch, the KP/31 was no lightweight. It tipped the scales at nearly 10 1/2 pounds, empty. This was nearly a pound more than a  M1 Garand! Slap a loaded 72 round drum magazine into the KP/31 (and you should!), and weight increased another 3 pounds. Lahti had given birth to a heavy baby boy. The upside to all of this steel meant that the gun was extremely durable and built to last.

This young lady doesn't seem to mind the weight of her KP/31 variant (with coffin mag), which is possibly a Swiss export model. The gun, not the lady.

The Finns put the KP/31 to good use against the Soviets in the Winter War and Continuation War. The gun fired ~900 rounds per minute, and as mentioned, had a unique quick change barrel which made it capable of long periods of sustained fire. Initially equipped with 20 round magazines, the Finns quickly realized this was inadequate and adopted a 72 round drum magazine, and then an interesting four column 50 round "coffin" magazine. Standard load-out during the Winter and Continuation Wars was either five drums or seven coffin mags, giving a soldier quite a bit of firepower. Typically, one soldier per rifle squad was equipped with the KP/31, making it the squad automatic weapon of its day.

Patent drawings of the original 40 round (later 72 rd) drum magazine (left), and quadruple column "coffin" mag (right).

Ergonomically (other than the weight), the KP/31 excelled. It came naturally to the shoulder, the wood stock provided a solid cheek weld, and it had a longer barrel and sight radius than its contemporaries. The weight of the gun actually did have a positive impact: it minimized felt recoil, but reports from the field showed that muzzle rise could be a problem. To counteract this, the barrel jacket was given an integrated compensator. This added about 2 inches to the already long-for-its-kind 12.5" barrel. Reportedly, Lahti was vehemently opposed to this modification as he felt the compensator decreased muzzle velocity and hurt the gun's reliability. All told, the Finns produced roughly 80,000 KP/31s and associated variants (some of which, like the tanker and bunker models, were really cool), with a very small percentage being exported. The gun stayed in front line service until the 1960s, when it was replaced by an AK style assault rifle known as the RK.62. Still, KP/31s were kept as reserve weapons until the late 1990s. Because the damn things just worked.

The Finns loved their Suomis (center), but they weren't above using captured guns like the excellent PPS-43 (left). Safety note: placing one's hand over the muzzle of an open bolt sub-machine gun is an especially bad idea.

Thanks to a myriad of restrictive laws, it's extremely difficult and expensive for an average American citizen to own a fully functioning KP/31. Thanks to American ingenuity, however, the average American can own a pretty cool facsimile of one. In recent years, a firm called TNW Firearms procured a large quantity of demilitarized KP/31 "parts kits". These were basically KP/31s that had been disassembled, with the receivers torch cut per BATFE specifications, but the rest of the gun was largely left intact. Taking these parts and a newly manufactured upper receiver, TNW re-built the KP/31, turning it from an open bolt, select fire submachine gun into a closed bolt, semi-automatic carbine. Outwardly, the only real distinguishing difference between TNW's semi-auto Suomi, and the real deal, is the barrel extension welded onto the original Suomi barrel in order to bring it to NFA mandated 16" length. I acquired mine about two years ago, which was toward the end of the production cycle. That's right: TNW no longer makes these guns. I asked them a while back if they'd make more, and their response was that they would not, since parts kits with serviceable barrels and stocks are no longer available in quantity. The price? About $500, and that included a sling, one 72 round drum magazine, and a 36 round stick magazine (the 36 round magazines are post WWII issue, and they work quite well).

With the 36 round stick magazine. Note the barrel extension is only slightly longer than the barrel jacket. Worth SBR'ing?

Overall, TNW's rendition of the KP/31 is a nice piece of kit. The stocks are like new and all metal is freshly Parkerized in dark gray (the originals were blued). You can see where they did some welding work, but though it's visible it's not what I'd call sloppy. Function? Mine's perfect. Some early TNW guns were striker fired and reportedly had issues; mine is hammer fired. The trigger pull is about as heavy as the gun (no exaggeration here, I'd estimate it's a good 10 pound pull), but ignition is positive. My gun has the integrated compensator on the barrel jacket (so-called SJR version). Best of all, TNW retained the quick-detach barrel system. Meaning, this gun is a prime candidate for a short barreled rifle conversion: once you pay the requisite $200 tax and receive approval on your ATF Form 1, you can attach an original Suomi barrel in seconds. I've not done that to mine as yet, but may get around to it someday. From the shoulder at 25 yards, the gun is as accurate as you could want, and will make short work of any tin cans on the berm. Firing a 72 round drum from this position does get a little tiring, but you probably won't care because of how much fun it is. If you can still find one, and you're someone who appreciates history and military firearms, I highly recommend picking up this iteration of one Mr. Lahti's greatest designs. You won't regret it. 

The last known picture of Aimo Lahti, taken 3 weeks before his death on April 19, 1970. He lives on through the firearms he created.

*For a treasure trove of info on Finnish weapons, including the KP/31, visit http://www.jaegerplatoon.net/, the main resource I used for this blog entry.

Adventures in Reloading: The 7.62x38mmR Nagant

There's still at least a dozen guns in the safe that I've not written about yet, but it's the dead of winter. We got 10" of snow last weekend in the Shenandoah Valley. Though I've done a bit of shooting in December and even one cold day in January, for me winter is really about getting ready to shoot when it warms up. So, I've been puttering around, checking inventories and determining what I need to load. Recently, I acquired another Nagant M1895, this one birthed in 1915, making it a cool 100 years old. Wanting to shoot the old girl, I checked my stocks, and discovered I was nearly zero balance on ammo. Time to fix that.

And then there were two. Top: 1915 M1895 Nagant, bottom: 1944 M1895 Nagant (Izhevsk)

When I bought my first Nagant, a 1944 Izhevsk, I didn’t like that factory ammo was hard to get, fairly expensive, and surplus ammo (at the time, anyway) was non-existent.  Internet commandos told me that the Nagant revolver could shoot the .32 S&W cartridges, and even the more modern .32 H&R Magnum, “without problems”. To that, I say Nyet, Comrade, that's not where you should be trying to save rubles. It’s never good practice to shoot a cartridge in a gun for which it wasn’t designed, so I discounted that “option” immediately. Besides, .32 S&W rounds aren't generally stocked at your local Wal-Mart, so that wouldn't help anyway. Reloading seemed the obvious choice. I do it for every other cartridge I shoot, and I wasn't about to let the peculiarities of the 7.62x38mmR change that. I decided that my criteria for reloading the Nagant would be as follows: the cartridges I made would have to be safe (good), inexpensive (cheap), and provide a gas seal (fast). Basically, I wanted a factory-type cartridge for less money, just like with any other reload, with no compromises. That's doable, right?

I like Venn diagrams, but this one is making excuses so I set out to prove it wrong.

Long story short, after some exhaustive internet research, in which a great many men opined, but only a select few spoke with Truth, here’s what I wound up with:

• Brass: Once Fired Prvi Partizan 7.62x38r
• Bullets: Grafs .308 98gr copper plated DEWC
• Dies: Lee .30 Carbine Sizing Die, Lee .30 Carbine Powder Thru Expanding Die, Lee .32-20 Bullet Seating and Crimp Die (modified), #19 Lee shell plate
• Powder and primers: IMR Trail Boss, CCI 500 Small Pistol Primers

Tools of the trade: Lee .32-20 seating/crimp die (disassembled), Grafs .308 98gr DEWC, and IMR Trail Boss

*DISCLAIMER: I am not a ballistics expert. Actually, I have a Bachelor's Degree in Political Science. If that doesn't scare you off, then I salute your bravery, but know this: following anything I've written after this point is completely at your own risk. If you are unwilling or unable to accept personal responsibility for your decisions and any potential negative consequences resulting thereof, then click here.*

The Dies: You could spend more money (a lot more) on bonafide 7.62x38r dies, but my “inexpensive” criteria ruled that out. Internet commandos told me I could use .30 carbine dies, and they were actually right! I already had a set of 30 carbine dies, and they resized the brass to within a couple thousandths of the factory rounds. Purchasing a .32-20 seating/crimp die was cheap. But Lee Precision had the *audacity* to design their .32-20 seating die to seat a .32-20 bullet, so alas, it wouldn't place the bullet deep enough in my 7.62x38r case in order to give me the coveted gas seal. So, I again deferred to the internet, which told me to cut a section of bolt, and put it inside the die to give some extra length to the seater plug. Lo and behold, it worked perfectly, the internet commandos are 2 for 2! The #19 shell plate came from my 9mm Luger die set, and the small rim of the 7.62x38r case fits it nicely.

Cut a 1/4" piece of bolt and drop it in the seating screw. Then reassemble. A *spent* .22 cartridge case could also work.

The Bullets: Projectiles were an easy choice, after researching. The Nagant’s bore diameter is a subject of debate amongst those who like to debate such things, but I'm not interested in debate, just facts. Here's the truth: the surplus Soviet ammo that I acquired mikes out at .308, so that’s what I went with. No sense arguing with Ivan, he knows best. Sure, I don’t doubt that you could use a lead bullet of .310-.311 diameter without problems, but the weight and caliber of the Grafs bullets are nearly perfect for the Nagant revolver (apparently Grafs has them made specifically for that purpose), and they were pretty cheap at $10 per 100.

The Powder: This part was somewhat of a leap of faith for me. Designed for cowboy action shooting, IMR Trail Boss is a fluffy, donut shaped, fast burning powder which fills cavernous revolver cartridge cases nicely. Believe it or not, IMR actually encourages you to experiment with it, which is both refreshing and kinda scary at the same time. The gist of the link above is that as long as you don’t compress it, you can pretty much fill any cartridge case to the end of the bullet, and have safe pressures. That would be a max load; taking 70% of that volume gives one a starting load. I settled on a load of 3.5 to 3.8 grains. I knew I wasn’t going to get top velocities, but I also knew I wasn’t going to blow up the gun or myself, so hooray. And the Nazis and Red Army deserters I'm shooting at are made of paper, so velocity isn't much of a concern. Primers were a no-brainer; I used what I had on hand, but to avoid confusion, any small pistol primer will do.

They're like little, gray, explosive donuts. Breakfast of champions.

The Process: I load everything on a Lee Classic Cast Turret Press. In my opinion, if you’re only going to own one press, this is the one to buy. It’s a great compromise between a progressive and single stage, and still allows you to load larger rifle cartridges (up to .30-06 with auto-indexing!) without any trouble. I set the sizing and expander dies up normally, and run the cases through as my Lee Autodisk Pro dispenses the Trail Boss. Seating the bullet and getting the appropriate crimp takes a bit a of time to set up correctly, but once it’s done you won’t need to touch the dies again. Here's how I do it:  First I screwed the seating die in to provide zero crimp, then I adjusted the bullet seating screw to seat the flat nosed wad cutter about 0.06” below the case mouth. This is a bit deeper than the commercial factory loads (but shallower than the ~0.08" below flush surplus bullet), but it’s necessary to get the correct crimp. Without a crimp, the cartridge will be too fat to enter the Nagant’s “forcing cone” (it doesn't have one, hence the quotes), and you won’t be able to cock the revolver.

This is a good indicator that your crimp is small enough to allow the round to chamber when you cock the hammer.

Once seating depth was where I wanted it, I backed out the adjustment screw completely, and screwed the die in about one full turn. I ran the cartridge through it and inspected my crimp. You really don’t need to crimp the case mouth too much…again, just enough to allow it to provide the gas seal. You want to use the least amount of crimp possible in order to prolong case life. I test fitted my completed cartridge after removing the cylinder from my Nagant . If it fits, place the cartridge back into the press, run up the ram and adjust the seating depth screw down until it touches the bullet. You’re done, and can now seat bullets and crimp the cartridge mouth in one smooth stroke for all subsequent cartridges.

From left to right: Ivan's cartridge (surplus), Fiocchi commercial, and mine (reloaded Prvi Partizan). The top of mine is shiny because I buffed with 000 steel wool so you could see the crimp better.

So, how do my reloads shoot? Better than I do, which is actually better than it sounds. The heavy single action trigger on the Nagant doesn't lend itself to accuracy, as I mentioned, but my rounds shoot at least as good as the surplus stuff, and a mite bit better than the commercial offerings. I have chronographed loads from 3.5 to 4 grains, and am seeing 930-990 fps. Though I don't know *exactly* what the pressures are, the cases drop out of the cylinder without trouble, ready for reloading again. And for less rubles. How much less?

1. Used brass: Free! (after the first shooting, anyway)
2. Bullets: 10 cents per round ($10 per hundred)
3. Powder: 1.5 cents per round ($16 per 9 oz can)
4. Primers: 3.5 cents per round ($35 per 1,000)

Total: 15 cents per round, which works out to $7.50 per box of 50. Compare that to $22 per box of 50 for commercial ammo, or $13 for surplus, and we have a winner.

Score one for the proletariat!

I honestly was quite surprised that my rounds are about as fast as the Russian surplus. I'd love to see real data on pressures and velocity from a major bullet manufacturer, or even better, a powder company, but until then it's Trail Boss for me. Regardless, there's something inherently Russian about reloading the 7.62x38mmR in this way: my reloads are definitely reliable and economical. I think the Party would be pleased, no?

And that's all that *really* matters, right?