G43 not cycling properly

[MGMike]

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

 

[GunKraut]

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.

^^^ This ^^^

as firing pins go, the g43's is pretty heavy, and does float, which --considering that these rifles were not built to the highest standards of gunmaking--is worrisome.

Actually, they were built to pretty high standards given what was available back then. The G43's integrated scope rail and the quick change 10 round box magazine were not shabby either. Due to the shortage of proper alloys needed for making steel tougher, Walther decided to forge the receivers which allowed for using lower grade steel while still maintaining enough operational margins. Some parts, like the bolt carrier, initially cracked after moderate usage and were re-engineered. Same for gas cylinders. Unfortunately, some late war design modifications with the goal of saving time and material were steps in the wrong direction as they introduced new weaknesses. The lack of receiver "meat" underneath the rear sight is the only major weak spot of the design. Reducing the height of the firing pin carrier from the original G41 design to the smaller G43 height adversely affected reliability. In all honesty, cracked rear receivers or cracked op-rods were not uncommon with the M1 Garand either and the fact that the Garand was designed many years ahead of the G43 allowed U.S. manufacturers to iron out the M1's design flaws and make it an apparently more mature rifle during WW2.

 

[Intruder196]

G43's can slam fire. I replaced the two recoil springs with brand new ones. Took it to the range and it was running fine on surplus 8mm until I put 3 rounds of commercial ammo in the mag and it slam fired all three. It ran away on me and I was glad it wasn't a full mag. The range made me put it away after that. Now that the springs are broken in it runs like it should with all ammo.

 

[M1-Garand]

G43's can slam fire. I replaced the two recoil springs with brand new ones. Took it to the range and it was running fine on surplus 8mm until I put 3 rounds of commercial ammo in the mag and it slam fired all three. It ran away on me and I was glad it wasn't a full mag. The range made me put it away after that. Now that the springs are broken in it runs like it should with all ammo.

The commercial ammo must have had very soft primers.

 

[MGMike]

...

Actually, they were built to pretty high standards given what was available back then. ....

I'm not sure you disagree. What was "available back then" to the Germans was: 1) dirty carbon steels, 2) slave labor from concentration camps, 3) a very short development curve, and 4) urgent pressure to increase production.

I'm not trying to be argumentative, but I wasn't referring to design features such as the scope rail or the detachable magazine; I explicitly referred to the manufacturing standards. In Germany's desperate straits, quality was pared to the minimum acceptable. What is remarkable is that the guns worked as well as they did.

M

 

[GSU]

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

Unless you were to shave the locking lugs or firing pin carrier fully flat, there is no way for a G43 fire out of battery.

I was more talking about the way the firing pin works, than the actual mechanism. The M60, FG42, and Lewis have to rotate the bolt into battery for the firing pin to hit the primer. The Maxim has to have the bolt face rise into battery for it to fire (as well as an auto-sear lever to be depressed).


The FN49, or any tilting bolt for that matter have a disconnector, but by design could still fire out of battery since the unlocked/locked position is very short and the hammer can still strike at both positions.

 

[MGMike]

...

I was more talking about the way the firing pin works, than the actual mechanism. The M60, FG42, and Lewis have to rotate the bolt into battery for the firing pin to hit the primer. The Maxim has to have the bolt face rise into battery for it to fire (as well as an auto-sear lever to be depressed).


The FN49, or any tilting bolt for that matter have a disconnector, but by design could still fire out of battery since the unlocked/locked position is very short and the hammer can still strike at both positions.

The distinguishing feature of the M60, FG42 and Lewis (and the critical one for the purposes of this discussion) is that the firing pin is fixed to the bolt carrier and cannot move independently. None of those guns has a hammer; the firing pin is driven into the primer only by the final movement of the carrier. The firing pin is not long enough to reach the primer until the bolt/bolt carrier assembly is telescoping into its shortest length, which happens as the bolt rotates to lock. They have plenty of momentum to complete that movement before full ignition.

In that regard MGs operating from an open bolt are probably safer than closed-bolt rotary-locked semi-auto rifles that have firing pins floating inside the bolt itself. I have examined both an M1 Carbine and a Valmet M71 (Kalashnikov variant), wrecked from firing almost out of battery-- the locking lugs being only in "toenail" engagement. The corners of the bolt locking lugs and receiver abutments were sheared off diagonally. Both were caused by using reloaded ammunition with mislocated case shoulders resulting in insufficient headspace. There was unfortunately enough slop in the mechanism to allow the trigger to release the sear and the hammer to fall and hit the firing pin without incurring a misfire.

As to "any tilting bolt" rifle, I have not recently examined an FN49 and will withhold an opinion on that. But I am persuaded that --based on my measurements and subject to the caveats I mentioned earlier-- the statement is incorrect at least as to the French M49/56. Its locked/unlocked transition is indeed short, but the firing pin is sufficiently shielded that it cannot be struck until the bolt has been pushed down into the locked position by the bolt carrier by a generous margin, not even close.

M

 

[GunKraut]

The G43 is not control fed in the same way the K98 is. When the K98 picks up a cartridge, the cartridge head is already resting firmly against the bolt face, held in place by the extractor. At any time before the bolt is completely closed, the bolt can be pulled back and the cartridge with it.

In the case of a G43, the cartridge is pushed out of the magazine by the rim of the bolt head, then gets pushed forward into the chamber by the face of the extractor claw. Before the bolt is completely closed, the bolt can be retracted, leaving the cartridge behind in the chamber. The extractor will not engage until the bolt is completely closed and in battery.
As long as the extractor is pushing the cartridge, there is enough of a gap to prevent the firing pin from touching the primer. Once the extractor spring force has overcome, the extractor will slip past the cartridge extraction rim. For this to happen, the cartridge has to be firmly lodged into the chamber to provide the resistance necessary to allow the extractor to slip over the rim. At this point, an out of battery detonation is impossible as the cartridge is factually in battery, even with the bolt not entirely closed yet.

With the cartridge in the chamber but the bolt not yet closed, the recoil springs push the firing pin carrier forward. As long as the extractor has not slipped past the cartridge rim, the bolt is still too far back to allow the locking lugs to engage with the receiver groove. The lugs are still folded inwards, preventing the firing pin carrier from going all way forward or allowing the firing pin to protrude through the bolt face, respectively. Only when the extractor slips over the rim, can the firing pin carrier spread the locking lugs into the grooves while traveling the final 1/4" forward into firing position. At this point, the inertia will cause the floating firing pin to put a small dimple in the primer.

If the rifle is poorly maintained, two possible causes can result in runaway fire: 1) Sticky firing pin, caused by contamination, carbon build up or bent/binding pin. 2) Rimming of the firing pin hole, caused by wrong/aftermarket firing pin or excessive dry firing without snap caps. In the latter case, the tapered tip of the firing pin will slam into the back of the bolt head (which is very thin around the firing pin hole) and displace material outwards, resulting in a rim around the firing pin hole which can be felt when running a finger over it. On rifles with loose head space, the rim can be tall enough to prevent the firing pin from protruding sufficiently and from reliably striking the primer. On rifles with tight head space, the rim can act as a firing pin and set off soft primers the moment the extractor slips over the cartridge. Rims can be pounded back with a large punch or a squared face metal rod. A third cause for runaway fire can be a malfunctioning disconnector, allowing the hammer to strike after each cycle as long as the trigger is pulled back.

In my opinion, it is technically not possible for a G43 to detonate out of battery except for catastrophic failure of the locking lugs or broken firing pin carrier.

 

[MGMike]

....

In my opinion, it is technically not possible for a G43 to detonate out of battery except for catastrophic failure of the locking lugs or broken firing pin carrier.

After spending this afternoon carefully studying my own G43, I believe you are correct.

The firing pin is allowed only about .050"-.060" free forward movement within the firing pin carrier; the firing pin carrier must travel forward approximately an additional 1/4" after the locking lugs have extended into their receiver recesses, before it gets close enough for the firing pin to protrude through the breech face. A catastrophic failure of both locking lugs seems improbable; their simple loss is more likely. A broken firing pin carrier would probably just jam the gun up.

As you point out, however, there is some risk of slam-firing. I found that if the long slender firing pin is bent even slightly (by only a few thousandths), it can stick in the forward position. Mine did. Up to a point, primer extrusion upon firing tends to shove it back flush with the breech face, but if the binding becomes severe, the gun may fire as the bolt slams shut. However, as we've discussed, it will fire locked -- not unlocked.

M

 

[bigwagon]

As to "any tilting bolt" rifle, I have not recently examined an FN49 and will withhold an opinion on that. But I am persuaded that --based on my measurements and subject to the caveats I mentioned earlier-- the statement is incorrect at least as to the French M49/56. Its locked/unlocked transition is indeed short, but the firing pin is sufficiently shielded that it cannot be struck until the bolt has been pushed down into the locked position by the bolt carrier by a generous margin, not even close.

M

I own both an FN49 and a MAS 49/56 and although I haven't had any slam fire issues, both rifles are known to occasionally have them for two different reasons. On FN49s with the original 1-piece firing pin like my Luxembourg model, it's possible for the pin to break, sticking the front section in the firing pin hole and causing the primer to ignite before complete lock up. Later models were converted to a 2-piece pin for this reason. On the Mas, the cause is inertia from the very heavy floating firing pin in combination with softer commercial ammo primer cups. There have been some aftermarket conversions to lighter titanium pins and also the addition of a spring to retard movement of the pin. I haven't had a slam fire with mine, but even hand-cycling live rounds from the magazine leaves a very significant mark on the primer. Not recommended to do that.

 

[M1-Garand]

Slam fires

I own both an FN49 and a MAS 49/56 and although I haven't had any slam fire issues, both rifles are known to occasionally have them for two different reasons. On FN49s with the original 1-piece firing pin like my Luxembourg model, it's possible for the pin to break, sticking the front section in the firing pin hole and causing the primer to ignite before complete lock up. Later models were converted to a 2-piece pin for this reason. On the Mas, the cause is inertia from the very heavy floating firing pin in combination with softer commercial ammo primer cups. There have been some aftermarket conversions to lighter titanium pins and also the addition of a spring to retard movement of the pin. I haven't had a slam fire with mine, but even hand-cycling live rounds from the magazine leaves a very significant mark on the primer. Not recommended to do that.

The FN49 that had a lot of slamfires and may still have were the Egyptian contract ones,since Egypt did
not find it necessary to have a firing pin safety incorporated in their bolts,all the other contracts did have them.I knew a gunsmith who had one blow up on him and swore he would never touch another one.
I have an Argentine FN49 in 308 and it does not even leave the slightest mark on the primer after cycling a live round.
When I buy a new to me semi,I disassemble it completely and check it for any malfunctions it may have,then I make a dummy round for it with a live primer and no powder of course and cycle it multiple
times and see if the firing pin leaves a mark on the primer.
Of course I never shoot any commercial ammo but only handloads with hard primers like CCI 34 or CCI200

 

[pathfinder]

The tail of the disconnector should rest against the sear bar all of the time except when the hammer pushes it back as the hammer resets. The spring should be strong enough to hold the hammer until the trigger is released. The pins are end drilled so that they can be flared to prevent them from moving (typical german parts assembly during the war).