Hakkaa päälle! (Suomi M31 review) Updated- Range Report

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Netpackrat
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Hakkaa päälle! (Suomi M31 review) Updated- Range Report

Post by Netpackrat » Mon Feb 25, 2013 9:25 pm

As I mentioned in another thread, I recently ordered a Suomi M31 rifle from Centerfire Systems. These are a semi-auto version of the FInnish Suomi KP-31 subgun, which was used to great effect against the Russians in the Winter War. They are manufactured by TNW Firearms, using as much of the original piece as possible. Ordering from Centerfire can often be kind of hit or miss, but they seem to be improving lately. They shipped fairly fast considering everything that has been going on, and I got word from my FFL on Friday night that it had arrived. Drove out to pick it up on Saturday morning. I'd hoped to hit the range with it on the way home, but he'd warned me that it appeared to have some issues and would need work first. :( So I took it straight home instead.

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Problems were as follows. First, the bolt was hanging up on something and sticking to the rear. Since the M31 doesn't have a regular handle on the bolt, or any kind of forward assist, that's a problem. Second, the safety was stuck. As in, could not be budged at all. That's right, both TNW and CFS shipped an inoperative gun with an inoperative safety. Third, it is missing the locking screw for the trigger guard screw. Lastly, the barrel and shroud are slightly loose in the receiver. The whole thing was pretty dry, stiff, and maybe a little gritty, so the first order of business was a disassembly for cleaning, inspection, and lube.

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Disassembly is straightforward. The charging handle is pulled back, which allows removal of the endcap, recoil assembly, and bolt assembly. The quick change barrel and shroud are removed by turning a lever downward, and then rotating slightly to disengage the shroud from its locking lugs. Then the barrel can be pulled straight out. The stock is held in by one machine screw, as is the trigger housing. The trigger group is retained in the housing by driven pins, so I elected not to disassemble it further at this time.

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Upon disassembly, I tried the bolt in the receiver again, and it slid easily forward and back once the trigger housing was removed. It appears to have been dragging on the hammer, which is a fairly common malady with AK rifles assembled in the US using original parts kits on US receivers with US trigger groups. No big deal, and can usually be remedied by polishing, lube, and/or allowing the parts to wear in. I was happy to find that the grit I'd been afraid was in the action did not appear to be present. It was just really dry, so I lubed the bolt up well before I put it back together.

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As mentioned, the safety would not budge at all. I ended up spraying some Kroil into the internals, and malletizing it. Once I got it to move back and forth a few times, it was usable. It definitely doesn't move easily, but at least it moves now. I worked a bunch of lube into the trigger housing and hopefully the entire assembly will loosen up with use. The trigger pull weight is well beyond the 8lb limit of my scale.

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Here is the missing locking screw for the trigger housing screw. I will call TNW for a replacement screw, but for now the housing screw is being retained by loctite.

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Above photo shows the locking mechanism for the quick change barrel. The shim is .005" thick, and needs to be about .015" thick to eliminate the slop that is present. I will most likely end up making my own from shim stock. I also found a place which sells another shim that goes between the barrel and the shroud, to tighten up the fit there as well. Not a huge deal, just another annoyance that shouldn't be present in a new gun.

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Barrel and shroud, note the non-functional muzzle brake, and the extension that was welded on to an original Suomi barrel to bring it to minimum legal length. They did a good, clean job of welding on the extension. The front sight is really wide...I am probably going to narrow it somewhat, and enlarge the notch in the rear a little, because as of now they are pretty hard to see.

Upon reassembly with lube, the bolt slid more or less freely and it hand cycles 9mm ammo from a magazine okay, though it is kind of smooshing the cases a little, thusly:

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It probably just needs a little work smoothing the feed path.

Range report to follow at some point yet to be determined. It's still pretty cold out there. I won't have much ammo anyway until my 9mm components from the Byrnes, and my dies from Grafs arrive. My timing on buying something in a caliber that is almost entirely new to me was not the greatest in the world. The two boxes of Blazer Brass I found locally was $25 per box. They had quite a few boxes of it at that price, go figure.

At this point, even with the problems, I would most likely buy it again. I am not downplaying them (they shipped a gun with an inoperative safety, a non functional bolt, a missing screw, and loose barrel, which crushes ammunition on the way in, for crying out loud!), but so far the resolutions of those issues have been fairly simple. I briefly considered sending it back, but the next one might have been just as bad or worse. I realize everybody is busy and trying to maximize their output, but there's minimum standards that need to be maintained, and which would have been simple in the case of this firearm, and they just didn't bother.

At some later time, it should be fairly easy to adapt this to take a red dot sight if I decide to do that. My FFL suggested a 20 power Unertl to go with the tripod and crank trigger that it needs. That's only a slight exaggeration, because it weighs a TON. I can see why they must have been so effective in the war, with all of the weight to aid control on full auto. A couple squads of snow camo clad Finns materializing out of the woods at close range with these could do a lot of damage to troops armed with Mosin Nagant bolt actions.

I doubt if there is much that can be done to put it on a diet... With the rifle disassembled, it's clear that most of the weight is in the receiver and bolt. The Finns built these to kill Russians with, and they built them to last so they could kill Russians with them for a long time. It's possible that I could save a little weight by paying $200 to the ATF, and obtaining an original length barrel and shroud, but that will only help a small amount. I may do it anyway. It would even be simple to shorten an original shroud further, leaving a portion of the barrel protruding, so that it could be threaded for attachment of a can, without making the overall length too long. But that's down the road a ways.
Last edited by Netpackrat on Sat Jun 11, 2016 7:23 am, edited 3 times in total.
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Kommander
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Re: Hakkaa päälle! (Suomi M31 review)

Post by Kommander » Mon Feb 25, 2013 10:51 pm

I would have just sent the thing back but some of us like a project.

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Denis
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Re: Hakkaa päälle! (Suomi M31 review)

Post by Denis » Tue Feb 26, 2013 7:43 am

Lucky you! Sounds like the teething troubles are under control, so well wear. That should be right at home with you in the frozen north.

rightisright
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Re: Hakkaa päälle! (Suomi M31 review)

Post by rightisright » Tue Feb 26, 2013 2:38 pm

Good review. My metal working/smithing skills are considerably less than yours so I would have been pissed off and sent it back.

Blessings for patience. 8-)

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Re: Hakkaa päälle! (Suomi M31 review)

Post by blackeagle603 » Tue Feb 26, 2013 6:08 pm

I love this bar.
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Netpackrat
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Re: Hakkaa päälle! (Suomi M31 review)

Post by Netpackrat » Tue Feb 26, 2013 7:12 pm

Well, all I have really done to it so far is disassemble and lube. It needs one locking screw, and I could just as easily stack original shims to snug up the barrel; I'm just going to make a new one because it is a cleaner solution. The thing with the ammo only really matters because I want to save brass for reloading.

[Edit: I just stacked the shims and it worked fine.]
Last edited by Netpackrat on Mon Apr 01, 2013 1:58 am, edited 1 time in total.
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Dinochrome
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Re: Hakkaa päälle! (Suomi M31 review)

Post by Dinochrome » Tue Feb 26, 2013 7:59 pm

Netpackrat wrote:Well, all I have really done to it so far is disassemble and lube. It needs one locking screw, and I could just as easily stack original shims to snug up the barrel; I'm just going to make a new one because it is a cleaner solution. The thing with the ammo only really matters because I want to save brass for reloading.
Yeah, it's too bad that many of these repurposed sub-guns damage the cases. The Finns didn't really care about all those Berdan-primed cases that they distributed into the Elder Snows all those years ago in the Winter War. I've heard the same thing said about the semi-auto Mark V Sten owned by a friend of mine; it dents every single one on ejection.
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Windy Wilson
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Re: Hakkaa päälle! (Suomi M31 review)

Post by Windy Wilson » Wed Feb 27, 2013 12:29 am

Gee, if that were available in semi-auto only, with 10 round mags, it doesn' t seem to have but one evil feature, so it could conceivably be legal in California (sigh).
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Netpackrat
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Re: Hakkaa päälle! (Suomi M31 review)

Post by Netpackrat » Wed Feb 27, 2013 7:54 pm

Here's what they sell as a project:

http://www.tnwfirearms.com/proddetail.php?prod=M31kit

It only saves you $100 plus FFL fees over buying one already built.
Windy Wilson wrote:Gee, if that were available in semi-auto only, with 10 round mags, it doesn' t seem to have but one evil feature, so it could conceivably be legal in California (sigh).
It is semi-auto only. And at the above link, they say they can supply magazines modified to only hold 10 rounds.
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Denis
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Re: Hakkaa päälle! (Suomi M31 review)

Post by Denis » Wed Feb 27, 2013 9:18 pm

Goodness, NPR - you do have a lot of Vise-Grips!

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