TNW Suomi M31 (KP/-31) Review

I have owned this rifle for a couple months, but just got around to publishing some thoughts on the TNW Suomi M31 (officially KP/-31).



This review will be broken into ten sections:

-About the Firearm
-Controls and Features
-Range Report
-Ammunition Tested

About the Firearm

Those of you who have followed Modern Rifleman for a while will remember the Winter War essay I authored back in April titled History: Winter War 1939-40. While writing that piece, I found myself captivated by the courage shown by the Finnish fighters in the face of a superior Soviet foe. In addition, I learned that the 9x19mm Suomi KP/-31 played a much more influential role in the conflict than I had initially believed. With its stifling rate of fire, low recoil, and high capacity Finnish soldiers, both on foot and skis, used the KP/-31 to great effect in frustrating the Soviet forces. After finishing the paper, I could not help but purchase this semi-automatic KP/-31 (M31) built by TNW out of Oregon. The rifle with three magazines and a sling set me back $450 before shipping from Centerfire Systems in Versailles, Kentucky.


Controls and Features

Upon picking the rifle up for the first time, I was amazed by the KP/-31’s heft, especially for a 9mm firearm. It seems everyone who owns or has shot one of these rifles says this, but until you hold the firearm in your hands it is truly difficult to understand not only how heavy it is, but also how dense the gun feels. Twelve pounds of rifle has literally been packed into a carbine-sized package.

Loading a magazine into the KP/-31 is a rather straightforward affair. The open magazine well has a channel cut into the rear that mates with a ridge on the back of the magazine. The magazine release is a paddle type that is located just behind the magazine and is protected from accidental engagement by a small steel guard. The KP/-31 is charged by pulling the cocking handle at the rear and right of the receiver near the grip. It should be noted that as a result of TNW’s decision to parkerize the rifle’s bolt, charging the firearm can be very difficult early on. I Personally recommend polishing the bolt or otherwise removing the finish to help relieve some of this friction between the bolt assembly and the inside of the receiver tube.

In order to avoid making a short barreled rifle (SBR), TNW added an extension to the original 12 inch Finnish barrel, but reports are that several of these rifles are shipping with newly manufactured 16 inch barrels. From my experience, neither configuration offers any real advantages in terms of real-world performance. The new barrels may offer slightly higher muzzle velocities, but both seem equally accurate. In addition, the barrel shroud can be removed by turning a lever on the right of the magazine well, rotating the shroud approximately 15 degrees and pulling it off.



The internals are parkerized in the same manner as the outside. As I previously mentioned, the bolt and charging handle both stick somewhat when charging the rifle and during disassembly. In order to the remove the bolt, simply pull the charging handle back and unscrew the cap (original part) on the back of the receiver. The bolt appears to be a modified version of the original KP/-31 bolt assembly. The rifle included the original trigger guard/enclosure, but a newly designed hammer-fired system has been installed as part of the conversion to semi-automatic. It is my understanding that this is a newer upgrade as the original TNW guns utilized a striker-fired system. The hammer-fired action seems to provide reliable primer strikes, but does not necessarily imply a lighter trigger pull. In fact, the rifle’s trigger is among the stiffest single-stage offering I have ever felt. The original barrel that is included with the rifle is reportedly user removable, but seems quite stuck on the rifle I received. In order to take full advantage of the swappable barrel, I will need to have mine pressed out by a gunsmith. The gun operates via straight blowback and a rubber recoil buffer can be found at the rear of the receiver that is intended to help with the rifle’s longevity.




There is no denying that World War Two era Finnish weapons have a sort of unmistakable, utilitarian beauty to them. Like the M/39s that are popular on the US surplus market, the KP/-31 features a wood stock with attractive coloration and grain. Unlike the original blued submachine guns, TNW has parkerized these rifles. This is a bit of a disappointment as the gray parkerization falls short of the bluing appearance-wise, but also because the thick, rough finish causes the bolt to drag while charging the rifle and makes it difficult to make necessary adjustments to the front sight. I understand that bluing would have resulted in a more expensive rifle, but the low quality parkerized finish takes away from an otherwise enjoyable firearm.

The original barrel shroud that ships on the KP/-31 is both attractive and functional. During my tests, I found that the shroud dissipates heat very well and seldom gets noticeably warm. The forward sling swivel is mounted to the left side of the shroud. Unlike Wiselite’s PPSh-41 builds, TNW opted to maintain the original length barrel shroud.



The sights on the KP/-31 are standard tangent sites similar to those found on the Mosin-Nagant and other military rifles of the era. The front sight is quite wide, making precision shots more difficult, but target/sight acquisition very fast. Out of the box, the rifle shot well to the right of the point of aim. Unfortunately, drifting the sight is incredibly difficult as a result of the thick parkerized finish. I have been told that an AK sight tool will work on these rifles and will be sure to update this review as soon as I try one. *Edit: I did purchase an AK sight tool and attempted to adjust the KP/-31’s front sight. Unsurprisingly, the tool was not fit for the job and the front post remains too locked in to move. It looks like this rifle will need to be boresighted by a gunsmith. I am disappointed that TNW did not take the time to at least boresight these rifles before shipping.


The KP/-31 shipped from Centerfire with one 36-round stick magazine and two 71-round drum magazines. All three are original pieces and feature attractive blued finishes. The drums open up very easily for loading. Simply press a button on in the rear-center of the drum and rotate the latch on the front. The stick magazine fed very well during my limited testing, as did one of the drum magazines. Unfortunately, the other drum came so covered in cosmoline that I did not get it cleaned in time for testing. I will continue to update this section moving forward, but will add that the rifle is very heavy (pushing 15 pounds) with a loaded drum inserted. It should also be noted that 50-round “coffin” magazines are available for the KP/-31.



Range Report

The KP/-31’s first trip to the range was largely a success. The rifle fed very reliably and produced consistent 3 inch groups offhand at 25 yards. I estimate the rifle is capable of shooting a ragged hole at that range from a rest. Though the heft of the firearm can be tiring during long shooting sessions it also helps to make recoil almost non-existent. I found both Federal and Prvi Partisan (each 115 grain) to be reliable and accurate out of the KP/-31.

My only gripes from my first session with the rifle both appear to be relatively easy to mitigate. First, the trigger is very heavy. I am not overly picky when it comes to triggers, but the trigger on the KP/-31 I received has at least a 15 pound pull. For reference, it is heavy enough that I could hold the unloaded rifle by the trigger without it breaking. My other complaint relates to the front sight and the parkerizing that has made adjustment nearly impossible without a press. I understand that point of impact can vary by ammunition, but to have a rifle that is consistently shooting to the right and is as difficult to correct as the KP/-31 is a little disappointing.


+ Reliable semi-automatic function

+ Very low recoil

+ Historically significant

+ Affordable ammunition

+ Impressively accurate

– Heavy

– Bad finish

– Difficult to adjust, poor sights

– Poor trigger



Based on the fun I had at the range with the KP/-31, I would be hard pressed to convince someone not to buy it. I love the historical significance that the firearm possesses and TNW has done an excellent job using as many original parts as reasonably possible. That said, I feel experienced shooters/tinkerers and military surplus collectors are best served by this rifle. Out of the box, buyers should expect to do some tweaking, but the simple mechanism lends itself to these sorts of necessary adjustments (cleaning up the finish on internals, polishing trigger parts, etc.). Despite some early frustrations, the KP/-31 (TNW M31) remains an affordable entry in the pistol caliber carbine market that should be very enticing to shooters looking for an affordable carbine that also happens to have some serious historical appeal.
Ammunition Tested

Federal Value Pack 9mm 115 grain (100% reliable)
Privi Partisan PPU 9mm 115 grain (100% reliable)


4 thoughts on “TNW Suomi M31 (KP/-31) Review

  1. Can you tell me where I can purchase the 50 round coffin mags.I can find the drums and 36 rounders but haven’t seen any 50’s.

    • Every now and then one will pop up on eBay or Gunbroker. They’re not cheap though. I think the one that is up on eBay right now is $130!

  2. At least yours was apparently in a usable condition as-received. They sent me a gun with an inoperative safety, a non functional bolt, a missing screw, loose barrel, and insufficient headspace, which caused it to crush every cartridge it chambered. I got it mostly sorted, and eventually I will cure the failure to feeds that it still sometimes suffers from.

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