a curious thing inside the MG 42 bolt

[Alexey931]

There is some guide rod and a spring on it, inside the MG 42 bolt. A rather biggish one, practically filling all the inside. My sources, otherwise comprehensive as well as reliable, just fail to mention it. Can it be some later development?

Best regards, Alexey

[striker754]

anti bounce assembly

[Karbinator]

It was on the original mg42's, as well as the later versions -- modern ones.
It forces the bearings on the bolt head outward, and into the barrel extension to
fully seat the bolt face to the breech (and ignite the pin on the ammo) all in one
spring loaded instant.
When this mg was invented, it was having some issues with out of battery explsns
until this device was incorporated.

[TOM R]

you do not use it on the semi bolt

[JBaum]

It isn't for forcing the rollers into the barrel extension, it's for keeping pressure on them so that they don't bounce out of locked position. The bolt would bounce when it hit the rear of the barrel, much like a hammer bouncing as it hits an anvil, and this would allow the bolt to be slightly away from the end of the barrel when the shot fired. This is called an "out of battery" explosion. You have to realize that at 25 shots per second, that it means 1/50th of a second is all it takes for the bolt to go completely rearward, and 1/50th of a second to travel forward. Figuring that over 90% of the 1/50th of a second is used for the bolt to move back or forth, it leaves only an extremely short time that the bolt is actually locked to the barrel. If the bolt bounces back, it is faster than the primer can ignite the cartridge, therefore the cartridge explodes without the bolt still being locked to the barrel, which means that the walls of the cartridge are not supported by the chamber walls and that allows the powder gas pressure to blow the cartridge to pieces. The spring pressure causes a momentary delay in the unlocking by pressing on the firing pin holder, which holds the rollers outward, and gives the cartridge enough time to ignite before unlocking can occur.

At least this is how I understand it.

The anti-bounce device was developed late in WW2 after trouble with bolt bounce. There are a few different styles of the device, but they all work the same.

[DARIVS ARCHITECTVS]

That's an excellent description of the function of the "bolt catch", John. You may have noticed also that the bolt catch is not just a metal weight, but is spring loaded much like a shock absorber. Being slammed back and forth between the rear end of the bolt and the locking wedge would certainly cause fatigue and damage to either the bolt catch or the parts it contacts after a while, so to prevent the damage, the bolt catch is designed like a weighted spring shock absorber. It can compressed ever so slightly under the force of being slammed against either end. The spring is pretty darn stiff though. WHen holding the bolt catch, you can compress it with your hand against a hard object to get an idea of how hard the spring truly is to conmpress. It give you an idea of how much farce can be applied in a bolt oscillating back and forth 20 times a second or so. It's weight presses against the roller locking wedge with just enough force and a long enough time to prevent the bolt from bouncing off the face of the barrel chamber, and allowing the rollers to fully engage and stay engaged during ignition of the primer. It's a carefully balanced and timed design.

[TANKER]

I'm glad to read these detailed explainations of the "anti-bounce" type bolt. I've seen three kits lately and two of them had bolts with no spring pre-load on the rear of the bolt. The third bolt, which appeared newer than the other two, has a very stiff spring pressure on the shiney cylindrical plunger on the rear of the bolt carrier,( for lack of knowledge of the correct nomenclature)
This last spring loaded bolt was in a post may dealer sample which worked very well indeed. Would it be fair to say that if you have one of the spring loaded "anti-bounce" bolts, that you should hang onto it as opposed to making a semi-auto bolt out of it ? Would the non spring loaded bolt carriers function just as well in a full auto. I do understand the the "anti-bounce" was a late? improvement to forstall out of battery ignitions. In other words: If you have your choice, use the anti-bounce bolt in a full auto and the non-spring loaded bolt carrier in a semi-auto bolt conversion. TANKER

[JBaum]

The anti-bounce device is completely removable from the bolt, and is a separate and independent piece entirely. The bolt either has the spirng loaded part inside, or it doesn't. The bolt itself is the same either way.

Correct nomenclature comes from getting a manual.....

The knob that rides in the feed cover lever is spring loaded on newer bolts so that the top cover can be closed with the bolt in the forward position. The anti-bounce device goes inside the bolt, and on the rear end of the bolt, it presses against the vertical pin of the knob that operates the feed lever. It doesn't push on the plunger at the rear of the bolt, which operates the ejector when it (the plunger) hits the front of the buffer when the bolt recoils. The front end of the anti-bounce device pushes against the firing pin holder (often called the wedge).

Running a full auto without an anti-bounce device is something that should be loudly proclaimed before putting in a belt. Thay way, the knowledgeable spectators can get away before t gun blows up. It will blow, it's just a matter of when. They're not used in semi-auto guns because they aren't needed as they fire from a closed bolt, so the bolt doesn't get the chance to bounce open in the split second that it takes for a slow primer to explode the shell. Besides that, the firing pin is in the way. Although I'm sure a design could be worked out to use the anti-bounce device with a semi, since there's no reason to, it isn't done.

[TANKER]

Running a full auto without an anti-bounce device is something that should be loudly proclaimed before putting in a belt. Thay way, the knowledgeable spectators can get away before t gun blows up. It will blow, it's just a matter of when. They're not used in semi-auto guns because they aren't needed as they fire from a closed bolt, so the bolt doesn't get the chance to bounce open in the split second that it takes for a slow primer to explode the shell. Besides that, the firing pin is in the way. Although I'm sure a design could be worked out to use the anti-bounce device with a semi, since there's no reason to, it isn't done.

Thanks for clearing that up ! However I'm wondering something......with so many of the bolts NOT have the anti-bounce mechanism, were out of battery explosions a common occurance during combat ? It seems that a firearm with such a great reputation would be reliable and "user-friendly" ....not killing or wounding it's crew?
BTW......where on earth can a fellow get one of those almost non-existant manuals?

[DARIVS ARCHITECTVS]

There was not a widespread problem of OOB explosions experienced by German soldiers, but Mauser did recognise that the potential was there and created the bolt catch device to reduce the possibility to an acceptable level. An original Mauser-made bolt catch is quite rare today, but plenty of postwar ones are available. Because most MG-42's operating today are so old, with mismatched and often badly worn parts, the potential for an OOB explosion is much higher than ever before. Headspacing is often unchecked by many MG-42 owners, and variations in used parts combined with wear can create a danger. I have seen one OOB in a MG-42, and believe me, it wasn't pretty. The bolt catch in that gun was actually cracked and broken, and the barrel locking piece was absolutely worn out, the barrel having been used for thousands of rounds of 8mm Turkish ammo, which is too powerful for an MG-42 and will eventually do damage. It's a miracle that the gun lasted as long as it did. It was a rewelded gun, had loose rails, and owned by a guy who did a very poor job of cleaning the gun. Bubba guns all blow up eventually.

[JBaum]

......where on earth can a fellow get one of those almost non-existant manuals?


click on the link to my website. If you want an original manual, they're a few hundred bucks. I sell my translations of the originals in English for a much better price.

[DARIVS ARCHITECTVS]

(John's Shameless Plug #4729. But who's counting . . .)

[JBaum]

Hey! He asked, so this one doesn't count. Encouraging someone to ask, then giving them the answer should be a freebie, right? hahahahhahahahahahah