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No. 108421
ID: bbee29
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>extractor chipped
>increased backpressure
Yep that makes sense looking at where it broke. I'd always start with a more open booster because running the gun hard will put a lot of wear on the ejector pin and other components. It's pretty easy to put in a tighter booster for more gas if it doesn't cycle fast enough and fails to eject rounds but the gun will beat its parts out cycling too hard but still cycle until it spits out guts. As stated earlier in the thread, mine was very overgassed at first and ate an ejector pin in ~20 rounds so I think I stopped and lucked out before anything else broke.
I've also made progress on the TNW MG34 on my end.
So I've been learning that the cyclic rate is affected by more than just booster port. Mainly, the firing pin spring. Mine seems to need a stiff spring as anything less doesn't seem to hit primers hard enough. In turn that'll slow the action down and it should make ejector pins last longer. I also think my main recoil spring (the big one) is a little weak. The barrel return spring might also need to get beefed up but it does feel quite stiff so I'm not going to mess with it now. Needless to say, making a handful of boosters at various diameters is saving my butt in this process. I found that pencil-testing my firing pin spring tension worked well. Assemble the bolt, cock it outside the gun, balance a pencil on the bolt face, and push the sear in to release the firing pin. At least three feet straight up for a regular pencil worked for me, less than that and I had failures to fire from weak pin strikes in good PPU 8mm (not really hard primer surplus). During my testing, the sear ended up wearing so I ordered some high impact resistant S7 tool steel. I'll be making new semi-auto sears and sear rings (not sure what that part is called, it's what the TNW sear catches to cock the firing pin) from S7, it should hold up quite a lot better than the buttery soft TNW ones.
I've also found some original ejector pins with the wedge-shape cuts that did help ejection quite a lot. I've replicated the original and my replica ejectors function perfectly. I made them from drill rod and gave them a quick heat treat only in the rear, and not too hard. Just a little bit to prevent the pin from deforming when hitting the ejector plate. Picture related, the original is on the left. Despite the shittiness of my garbage chinese """metal""" lathe, it makes quick work of this kinda part and I just hand filed the rest of the features.
Other than that, stoppages were mostly belt related. The TNW 34 advances the belt as the bolt is moving forward, so there's energy lost from the main recoil spring simply from advancing the belt to ready a fresh round. As the bolt is then moving a bit slower, it can be slowed down too much during feeding if the link holds the round too tightly. I'm not sure why they did it that way, I would have thought that a system that advances the belt as the bolt is opening, taking advantage of the recoil power, and only advancing the pawls (very little force required) would leave the bolt with as much energy as possible to strip a round from the belt and push it in the chamber. As a result, mine seems sensitive to how tight the belt is on the actual rounds, this could be exacerbated by the old main recoil spring. When I find belts or specific belt links that feed well, I push a round through it with my fingers (no gun, just holding everything in my hands), and then check tension by comparing other belt links. They're often much too tight, and require very carefully prying them open just a tiny bit. I carefully pry them open with needle-nosed pliers, matching the case taper as carefully as I can, and testing with a round to get the right tension. I might make a tool for this that can pry the belt link to the right tension automatically as I've bought like 25 belts and most of them have links that are too tight. Like many guns, once the minor issues with gassing/springs are resolved, the rest of the troubles end up being shitty magazines or in our cases, belts that just aren't quite right. I suggest you have a go at feeling your belt link tension as I think it's one of the final things to square away before the gun gets really quite reliable.
it's nice having belts and starter tabs now but the issue is buying enough ammo to fill 25 belts f f f f f u u u u c k
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