spring assembly in M53 bolt

[flemgunner]

Howdy Im wondering about a spring assembly that is in one of my M53 bolts. It fits inside the rear portion of the bolt and has metal "tips" on each end. Can anyone tell me what this is and what function it has? Also does it have to be installed for the bolt to operate?
Thanx

[DARIVS ARCHITECTVS]

BOLT CATCH SAFETY DEVICE 101

What you are describing is a safety device known as a "bolt catch". It consists of a spring loaded weight which can compress slightly when it slams into the roller locking wedge.

What it does: When the bolt travels forward, there is a possibility that the bolt can bounce off the chamber face if the rollers do not lock up. When the cartridge fires, a partial or incomplete roller lockup can result in a premature release of the bolt while the gas pressure is high in the barrel, causing great damage to the fun and you. What the bolt catch does is travel forward with the bolt and slams forward under its own inertia against the roller locking wedge. The additional weight forces and holds the rollers in the locked position for those few milliseconds which the bolt slams against chamber face and tried to bounce rearward. In effect, it "catches" the bolt by holding the rollers outboard so the bolt cannot move rearward during the ignition time.

How it works: Now, if the bolt catch were simple a steel weight, it would bounce off the roller locking wedge like a ball bearing dropped on an anvil, much like the bolt can bounce off the chamber face of the barrel. If it did that, it would not be doing its job. So, the bolt catch itself is a spring loaded shock absorber. It holds pressure against that locking wedge for a small time period. Imagine you jumping on a pogo stock. You and the pogo stick are in contact with the ground thoughout the entire time you are deccelerated, stopped, and accelerated skyward. This is unlike a bouncing ball bearing that only touched the ground for a tiny fraction of time before leaving contact with the ground. As the bolt catch contacts the locking wedge, it compresses, then its spring causes it to expand, all the while putting pressure on that locking wedge. This insures that during the ignition time period, those locking rollers STAY locked and that bolt STAYS held against the breach of the barrel.

What happens if I remove the bolt catch?: about 99.999999% of the time, the bolt stays locked properly during firing. However, the Germans recognized that one a full auto MG-42, a bolt bounce, and open breach during firing, COULD occur, and Mauser invented the bolt catch in 1944 to remove the possibility of MG-42's blowing up in their soldier's faces from a cartridge "out of battery" explosion. Even though your gun is a semi auto, and does not fire so soon after chambering a round, since it takes time for the hammer to fall onto the firing pin, you should STILL use the bolt catch device in your bolts to make darn sure that those rollers are FULLY locked before ignition occurs.

ALL OWNERS OF THE MG-42 OR M-53 SHOULD FULLY UNDERSTAND HOW ALL THE PARTS OF THEIR GUN FUNCTION AND THEIR PURPOSE, INCLUDING THE BOLT CATCH. Anything less when dealing with high power weapons leaves you vulnerable to having a CATASTROPHIC ACCIDENT!

[cz2]

DA,
What am I missing here? The" bolt catch" fills the space needed for s.a. firing pin,correct? I sure do not see how the "bolt catch"could be used in a s/a mg-42 conversion.The firing pin return spring,in the s/a conversion, seems to act in some what the same fashion except with considerably less dampening force on the wedge.
later,cz2

[flemgunner]

Thanx for the write up on that. My main confusion was in the fact my WW2 german bolt doesnt have one but my 53 bolt does. Im guessing the 42 bolt may be early and just didnt have the extra safety device? Also its for a full auto post sample. I wanted to check this before test firing "dotting the I's" so to speak. Thanx much man

[DARIVS ARCHITECTVS]

You're right, cz. There is no bolt catch in a SA M53. So, what is he talking about? He described what sounded like a bolt catch to me...

[flemgunner]

Its the anti bounce bolt stabilizer (just found it in the sticky section). I think what you were describing was right you just gave it a different name.

[drooling idiot]

BOLT CATCH SAFETY DEVICE 101

Even though your gun is a semi auto, and does not fire so soon after chambering a round, since it takes time for the hammer to fall onto the firing pin, you should STILL use the bolt catch device in your bolts to make darn sure that those rollers are FULLY locked before ignition occurs.

The design of the SA firing pin should prevent the tip of the FP from being able to reach the primer unless the bolts rollers are locked to the barrel extension.

[JBaum]

The full auto MG fires from an open bolt at 25 shots per second, which makes it susceptible to bad things with a bolt bounce.

The semi MG42 fires from a closed bolt which is not vulnerable to the same problem, so the semi gun doesn't need a bolt catch. Besides, with the firing pin, etc. inside the bolt housing, there's no room for it.

[Bil]

While DA has confused Halloween with April Fools Day-you should have seen his costume last April,he didn't get much candy-I would point out that Flemgunner is the proud ovner of a new bouncing baby FA post sample.Where are the cigars??? ---bil

[flemgunner]

[Blanksguy]

flemgunner,

Along with the "bolt-stabilizer" (and that the "Firing-Pin-Holder" has been updated with the second cam-surface at the top)......a couple of other things you should check prior to going to the range with a Full-Auto MG42:

1: Condition of "Recouperator-Assembly" to insure that the barrel is returned to the forward position prior to the bolt pushing the next cartridge forward from the feed-tray.

2: Condition of Cam-surfaces in the Trunnion to insure the bolt unlocks correctly.

3: Condition of "locking-slots" in barrel-extension on the barrel (and bore).....and that you have the correct caliber barels for the ammo you are taking to the range.

4: Correct Booster-Cup/"Nozzle" for your caliber "and" that you start with the shorter Barrel-Bearing so that the gun will initially fire slower.

Condition of other parts and lubrication of the gun will be important also....as will condition of belts and ammo.
Taking your spare barrels and bolts with you will be a good idea so that you can check these at the range.

And last.....your paperwork/registration/license.

Regards, RichardS in MI.
Blanksguy2001@chartermi.net

[flemgunner]

Cool thanx for the info man, much appreciated

[JBaum]

flemgunner,

2: Condition of Cam-surfaces in the Trunnion to insure the bolt unlocks correctly.

Blanksguy2001@chartermi.net

Trunnion? On an MG42? Where's that - mine doesn't have one!!!

[DARIVS ARCHITECTVS]

flemgunner,

Along with the "bolt-stabilizer" (and that the "Firing-Pin-Holder" has been updated with the second cam-surface at the top)......a couple of other things you should check prior to going to the range with a Full-Auto MG42:

1: Condition of "Recouperator-Assembly" to insure that the barrel is returned to the forward position prior to the bolt pushing the next cartridge forward from the feed-tray.

2: Condition of Cam-surfaces in the Trunnion to insure the bolt unlocks correctly.

3: Condition of "locking-slots" in barrel-extension on the barrel (and bore).....and that you have the correct caliber barels for the ammo you are taking to the range.

4: Correct Booster-Cup/"Nozzle" for your caliber "and" that you start with the shorter Barrel-Bearing so that the gun will initially fire slower.

Condition of other parts and lubrication of the gun will be important also....as will condition of belts and ammo.
Taking your spare barrels and bolts with you will be a good idea so that you can check these at the range.

And last.....your paperwork/registration/license.

Regards, RichardS in MI.
Blanksguy2001@chartermi.net

Add to that:

1a) Recuperator springs should be replaced as a set if they are weak. Weak recuperator springs will allow the barrel to move rearward too far during firing, and the bolt locking piece will slam into the ears of the camming piece cams, eventually breaking them off.

2a) Look at the forward ears of the camming piece. If they are chipped or broken, either the ammo you have been using has been too powerful in powder charge or the recuperator springs are weak, or a combination of both.

5) Bolt rollers. They can chip and crack after lots of use.

[bmg17a1]

I would offer one additional piece of information to the well written description of the issue of out-of-battery ignition noted above in the beginning of this thread. Headspace of the MG42 type guns should allow a small gap between the breechface and the boltface on lockup of the bolthead in the barrel extension. This gap is on the order of .002-.004" and serves several functions. When the chambered cartridge is fully forward and the bolt is fully in battery the breechface should not impact the breechface too heavily, as the cartridge case absorbs some of the impact. An out-of-battery ignition is actually a consequnce of two mechanical actions: the result of the bolt recoiling slightly from impact with the breechface/case, and the oscillation of the rollers in the lockup channels. OTB ignition was a fairly common problem for the military throughout the use of the MG42 in combat. The Germans discovered through highspeed photography, that the rollers oscillate in and out during lockup, and could move as much as 1.5 mm inward from initial momentum towards full lockup. If primer ignition occurs during the inward movement of the rollers, the direction of unlocking of the bolthead, then the bolthead is not fully locked into the extension and the cartridge case can force the bolthead back on ignition resulting in a detonation.
In order to alleviate the potential for this combination of mechanical actions, and to avoid OTB ignition, the Germans altered the ignition timing of the primers for ammo specifically made for MG42s. Apparently this was successful since the bolt catches were not employed in 42s until after the war was over. Four different types of bolt catches were made, with the last model used with the MG3s.
Of course, special MG42 ammunition has not been available for many, many years and most shooters use standard rifle ammuniiton in the guns, whether in 7.92 or .308, so use of the bolt catch is mandatory.
Other factors can contribute to OTB ignition, one of which is broken or compromised recuperator springs, which will delay the return of the barrel to rest, with ignition occurring while the bolt is fully in the barrel extension but the extension is not fully forward insuring full lockup of the bolthead.
I have rebuilt over one hundred recuperators installing newly made springs, and found that most of the recuperator springs in the housing I've repaired were broken near one or both ends of one or more of the three captive springs, or the springs had taken a significant set and were quite a bit shorter than an unused spring and were no longer capable of exerting sufficient return energy to move the barrel swiftly back to rest while firing.
One of the design oddities of the MG42 is the recoiling barrel and the impact of the tips of the curved piece unlocking ramps against the inside of the extension around the breech. If one looks at the inside face of the extension at each corner it is possible to see small silver squares where the tips of the unlocking ramps impact the face. Under ideal mechanical circumstances the recuperator spring system would be designed to prevent the impact, absorbing the recoil of the barrel, and returning the barrel swiftly to rest, but never allowing the tips of the ramps to impact the inside face of the extension. Of course, such a sensitive balance is not possible for many reasons. Thus, the impact is part of the harshness of the recoil impulse of the 42, and if the springs are consistently to correct spec, the impact is minimized. Compromised recuperator springs allow the impact of the inside of the extension on the tips of the curved piece lockup ramps to increase as the springs deteriorate eventually to a point where the tips of the ramps crack and break off. The curved piece is a extremely hard alloy and thus quite brittle, and If this damage is not rectified, further damage to the curved piece and even to the recuperator plunger and housing can occur.
I have quite a collection of severely broken and damaged curved pieces from the breakdown of the recuperator springs.
Hope this helps.

Bob Naess
Black River Militaria CII

[CRUSADER]

...bolt catches were not employed in 42s until after the war was over.

What makes you say this?

The rest of your post is very informative.

Is there a source for new barrel recuperator springs? Reading this thread makes it clear that having a few sets in my 'Spares Box' is necessary.

[flemgunner]

I bought a couple different recuperators and took em apart. Then I used the best spring s out of em to make one good recuperator

[CRUSADER]

The MG3 recup is longer than the MG42 recup, correct?

Since a MG3 recuperator is not a 'drop in' replacement in a MG42, does anyone know if the springs themselves are interchangeable?

*edited for question content*

[bmg17a1]

...bolt catches were not employed in 42s until after the war was over.

The bolt catch wasn't devised for use in 42 bolts until post-war, most likely for arsenal rebuilds of WWII guns and the early Rheinmetall 42/58, MG1s, etc. From what I undertstand from the researched history of the 42, there is no mention of the bolt catch in any German publications during the war, although there is full documentation of the OTB ignition problem and the means by which the problem was analyzed and then controlled, which did not inlcude the catch. I'm not a researcher, so this isn't my information, but have a long time Norwegian friend, Folke Myrvang, who has published a very comprehensive book on the 34s and 42s from who I've gotten a lot of historical information.

I have newly made recuperator springs for the WWII unit, with which I have been rebuilding them for fifteen years or more. I prefer not to sell just the springs, but will rebuild the units when sent to me. The reason I do not sell the springs is that too many of the recuperators that I've rebuilt have a mix of MG3 and MG42 springs, keepers and plungers, and I do not agree with the general belief that mixing these parts is OK. I can't control the use of my springs if someone rebuilds their unit in a manner which I believe is incorrect and then has any kind of damaging consequences that could be claimed were the fault of my springs.

Bob Naess
Black River Militaria CII

[bmg17a1]

Crusader writes:
Since a MG3 recuperator is not a 'drop in' replacement in a MG42, does anyone know if the springs themselves are interchangeable?

The MG3 recuperator was designed for the .308 round, whcih has a distinctly different ignition impulse and characteristics. The double twist construction creates different specs to the mechanical action of the spring. The ID of the MG3 spring is smaller than the MG42, thus the plunger shank OD and the ID of the MG3 keepers is smaller. Although I have not compared the compression rates of the MG3 springs to the 42s, their very different construction and other specs from the 42 springs, plus the extra length of the MG3 housing certainly indiacate a completely different set of mechanical properties. I do not advise mixing the MG3 springs with the MG42 springs or the plungers and keepers, although I do get recuperators from owners of both selectfire 42ds and semi 42/53s with these parts mixed. The MG3 plungers wil fit into the 42 springs and keepers, but the tolerances are way out of kilter. I've received and repaired a number recuperators which had the 42 plunger/springs used with an MG3 keeper and the plunger had been driven into the keeper destroyng the function of that spring and keeper in that unit.
So, I don't mix the two types of parts, or use MG3 parts in MG42 recuperators.

Bob Naess
BRMCII