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BRP has Suomi parts as well. Maybe you can make out better there. BTW, what is the differance between the M31 FA recoil spring and the SA spring? I have a TNW M31 and thought about buying a kit for spare parts, mainly wanting a spare extractor and recoil spring.
 

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The original SA spring they included with the kit was slightly larger (OD) and not as stiff as the stock FA spring. Unfortunately I wound up cutting the spring (due to my own ignorance and TNW's shitty, not to scale instructions) TNW wound up sending me another FA spring as a replacement. I just cut it down to where I can get the gun to manually strip, feed and extract with no issues. I havnt test fired it yet. I hope it works because after this much hassle, I know theres no way I can count on TNW for any kind of tech support.
Please let me us know if the FA spring works. I have a feeling that the TNW SA spring is on the weak side anyways. One other thought is perhaps you can use the cut SA spring and use part of the FA spring as a shim to bolster it.

I had a few issues with my TNW M31 at first BTW. I got it running 100% now using WWB 9mm running drums last time I took it out. I also have an easy fix for the terrible trigger pull on the TNW M31 if you are interested.

I found mine likes to run on the dry side due to the tight tolerances. If I oil the bolt it slows it down (oddly enough) inside the tube receiver. I took the rate reducing valve and spring out and that seems to get it to strip rounds better as well....I figured its not needed on an SA rifle and may actually cause problems.

If you have trouble getting drums to run let me know and I can post some pics on the mod I did to mine, along with the trigger mod.
 

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What kind of trigger mods did you do? ALL TNW triggers suck. My MG34 is horrible too.
Right now it hand cycles real nice, but Im afraid I cut too much off the recoil spring and its not going to strip rounds off a full magazine or drum.
I'd leave the recoil spring on the heavy side so it can strip the rounds, the drums have a lot more spring pressure than the stick mags. You can always cut one coil off at a time later after you test fire it if need be.

Speaking of drums, mine seemed to like less spring pressure, some guys have better luck adding spring pressure to their drums - not me, I went the other way. I tested 6 drums and noted which were heavy and which seemed weaker...this can be adjusted BTW.

A lot of these guns the rounds will strip fine with stick mags, but choke on drums (at least mine did). On mine, when I tested drums (stick mags were fine), the rounds nosed up jamming above the chamber. I noted that the frontal feed lips on the drums sit a bit higher than the stick mags. So I filed some of the front feed lip down (see pic with screw driver pointing it out). You may not need to do this...but keep this in mind if you have issues. I can now run that drum the full 70 rounds without any problems.



There is an easy fix for the TNW M31 trigger. Take a really thin peice of wire, you don't want too thick of one because then your trigger may not reset, that or it could cause it to double. Take the pin out (shown in the pic)...it just pushes right out and doesn't hold anything in place. You will need to press down on the bar under it with a screw driver to get it to slide out.

Now wrap the pin tightly with the wire, making it look like sort of a spring. You only need a few wraps. Slide it back off for now. Use a screw driver to press the bar down again and drop the paper clip part into place so that you can slide the pin back in.



If done correctly your trigger pull should be much lighter now. That said, make sure it still resets properly and the safety still works. Again if you go with too big diameter wire it can cause problems with doubling as well. As with any trigger mods caution should be used here for obvious safety and legal reasons.
 
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