While a slam fire is entirely possible and has probably happened at some point with the G43, I don't think it is able to fire out of battery simply by the design of the firing pin carrier and locking lugs.
For the firing pin to reach the primer, the firing pin carrier has to be pushed forward, pushing out the locking lugs.
If the lugs cannot extend, then the firing pin can't reach the primer.
Same with how a lot of open-bolt machine guns work (best that come to mind are the Degtyarev series, or the Maxim (closed bolt with a rising bolt face), but also the M60, FG42, or Lewis)
I understand that is how the G43 is supposed to work. My question was whether there is enough slop in the fit of the parts to negate that intention. This can only be determined by close examination and actual measurement, and in any event is subject to certain assumptions, in particular that the sample gun is dimensionally representative of all examples of that model, that the parts remain intact without breakage, and that the ammunition is not defective.
The Degtyrev's locking system is closely analogous to the G43's, but the M60, FG42 and Lewis are not. All of the latter are rotating bolt designs that collapse in length when they lock; the firing pins are mounted on the carrier and are not long enough to extend through the breech face until the bolt has rotated to a (mostly) locked position. I'm not sure about the Maxim, which is completely different and would require more study than the G43.
I once spent an afternoon with a micrometer and feeler gauges examining a French M49/56 rifle, a tilting-bolt design that relies entirely on geometry to prevent firing from hammer follow-down. This was prompted by a slam-fire incident the day before; fortunately the muzzle was pointed downrange. I concluded that, subject to the assumptions mentioned above, there was a wide safety margin that positively prevented protrusion of the firing pin until after the bolt was locked. So while a slam-fire from firing pin inertia was possible, an out-of-battery firing was not.
M
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