Receiver rail guide.
 

On shooter Lugers, this part of the frame sometimes breaks,is there anyway if you are going to shoot an old Luger to keep these two small parts intact? The two 1/16th inch parts that the receiver rides back on at recoil.

I think if I had it oiled really good this would not have happened?

You managed to *break* a receiver rail??? We need pics...

Do you refer to the two pieces of metal that stand upright at the rear of the frame? These were so 'important' that the Swiss deleted them in their 06/29 model, and Mauser also never bothered to add them to their Swiss inspired 1970s design.

They are like an appendix in a human body. You can live quite well without :)

just so we're all on the same page...the 'rails' are the ~1/16" x ~4" long protrusions on the sides of the receiver that run inside the grip frame...Under recoil, the receiver only travels about 3/8" using these rails...

If these are what you are referring to, I would like to see a pic...

If they are the two 'fins' sticking up on the abutment at the rear of the grip frame, that Vlim referred to...I would still like to see a pic...

How did you ever manage to break either of these two possibilities???

The fins, that is correct guys, THANK you. I had several Lugers years ago that the things were long broken off, and they appeared to me as exactly how Vim you described it, they look like they serve no purpose whatsoever. A waste of a machining step. I studied it and studied it and was trying to figure out why they were even put in the frame.

I put 600 rounds through it, (I mean it is a 90 year old gun)and that happened. I have a back up ejector, I bought a extra firing pin, the extractor, I guess I will wait..And as far as how did I manage it? WHo knows, I guess she is tired, I seen a lot of Lugers and owned 2 that had one of these fins broke off.

Hi:

I've seen a number of these fins rather mutulated by what I call breach block slap. This is when the ammo being fired is so hot that it causes the breach block to slap the frame, right at that point.

As this is a chief cause for mechanical failure of a Luger, you might try lighter handloads if your reload. If not, watch the commercial ammo you are using is not NATO spec or +P.

Sieger

Here's a pic to illustrate the point...Note the imprint of the rear of the breech block on the frame abutment...

1969goatman - Can you post a closeup pic of the inside part of the abutment (like the pic above) so we could see how badly the abutment has been battered??? It's been said here that the "Mauser Hump" was incorporated into the grip frame to eliminate the problems caused by excessive 'abutment' battering (namely, the toggle axle pin becoming fully exposed in recoil and popping out)...

In fact, if it seems to you that it is 'battered', maybe post a pic of the assembled pistol w/toggle in full recoil (you'll have to hold it back with your hand) showing whether the toggle axle flange is fully exposed...

Here's a pic of my S/42 (same gun as pics above) showing the relation of my toggle axle pin to the frame ears, in full recoil (I'm pushing it back with my finger), and having the breech block imprint on the 'abutment' as shown in my pic...Not too bad, even considering this frame does not have the "Hump"...

It would seem to me that under full recoil with a 'hot' load, the 'abutment' is being hammered from both sides...The breech block hitting it in front, and the rear toggle 'lip' hitting it from the rear...

It would be interesting to mic [measure the width with a micrometer] the 'abutment' of a severely hammered Luger (one with a chipped toggle axle pin and/or missing 'fins') to see how much it had shrunk from the hammering...

(Rich B goes into safe and starts jacking toggles back to check) :D

Hi Rich, There is no difference in the over all length of a Mauser frame (120mm) with or without the "hump". The hump is not formed by adding additional material to the back of the frame, but by removing metal from the lower half of the back of the frame. Imperial era frames were 1mm shorter, and they had the axle pin jamming issue. Regards, Norm.

Thanks for clearing that up for me, Norme! From what I had read, I had gotten the impression the Mauser Hump was added sometime in the 40's...

Just for giggles, I mic'ed my three grip frame 'abutment' widths, at the point of most wear...

S/42 = .255"
6782 = .250"
86434 = .253"

Interestingly, the 86434 shows no imprint of breech block or toggle 'lip' marks (it's a commercial 7.65 cal)...and the 9mm S/42 (pic somewhere above) with the sharpest breech block impression measures the greatest width...

I can't find a dimension on the blueprint, so I don't know if these are just tolerance variations or 'hammering' changes...

Hi Rich, I believe the axle pin jamming problem only became an issue post WW1, when hot 9mm ammo, intended for SMG's, was used in Lugers. This was corrected by extending the rear of the frame 1mm, on all Mauser and Krieghoff produced Lugers. I have no idea whether Simsons were also lengthened. What do you say, Ed? Regards, Norm.

So you want a close-up like the one above? I was using factory loads, Fiocchi. At one point (The day that I noticed this fin was no longer on my gun) the toggle locked back on firing it. It was as if the hold open was activated, but there were rounds in the mag, toggle locked back, this was the only time out of 500 rounds this gun ever did this (TO ME). As a matter of fact this is the only time this gun ever failed to feed for me. I am starting to believe at this point, is when this fin snapped off the frame.

I had a VOPO that had one of these fins busted off and one other Luger. Being they are so thin, to me it seems maybe just a little logical that in time (We are talking a 90 year old gun, that looks well used) that these little 1/16th pieces of steel would eventually fatigue and break. SO to me, I think it goes with the territory of wanting a 90 year old gun as a shooter?? I will post the image as soon as I can guys and I never expected such elaborate answers. Thanks to all of you.

BTW, Postino, without sounding like a total idiot, I am unclear of what I am looking for on this image you posted, .I still am going to fire this gun, it works great. Had I had a lot of grease on this area, or oiled good, this might not have happened.

It's not all dependent on the ammunition. A weak recoil spring could cause excessive pounding on what I call the 'abutment'. Here's the areas I am referring to - yours compared to my commercial...

It looks like yours has taken a bit more hammering than the commercial...And yes, being hammered from both sides could cause that 'fin' to work-harden/fatigue and break...

There really isn't any other stress on these 'fins'...Under normal operation...

If it were my Luger, I would be concerned about the breech block cracking...

But everything is relative! If you're happy with the way it functions, then that's all that matters! ;)

Should I change the recoil spring? Also, after this episode, it is sorta going into retirement. Explain why you think the breechblock would crack?Would a new spring correct this opinion you have? If this spring has never been changed, i would assume it is worn, BUT I AM CHANGING IT! what would you recommend? A 36 pound, 40 pound?? ARE WOLF springs good? A stronger spring puts less wear on these parts, the toggle train, is this correct? In all my years of Luger collecting I have never heard of anything breaking but the parts like firing pin, extractor, ejector and frame fins. But get this, I just read about a frame cracking. Now come on..how often does this happen?

Thanks again.

I think I understand what your saying, with the gun dismantled, the receiver slides all the way back to that block, (Cam) so it say. What your referring to (The ambutant thing or whatever) is the amount of restriction the recoil spring puts on the receiver for when the spring is engaged, for the receiver will only move back so far, so in other words, I can now see, with a worn recoil spring, how this distance would be greater (Just as if there were no spring) and you would have metal to metal contact on these parts, is this correct? DAMN, I wish I knew this. I was going to change the spring too.

I cannot tell by my hand, if the spring is worn. The toggle is not easy to move back, but I have had some Lugers that were very strong, like my New Mauser's I had. You learn something new everyday, and just goes to show you, as much as you think you know, there is always a ton of more. Thanks again.

And how are you pronouncing that AM BUT ment???

It's abutment -

Abutment - Definition and More from the Free Merriam-Webster ...
the part of a structure (as an arch or a bridge) that directly receives thrust or pressure

Now, as to the recoil spring...Yes, if it is weak, the breech block will slam into my abutment...and it it does, it will leave an imprint on my abutment...kinda like the one on your abutment...The breech block has thin walls, they weren't designed to be slammed around...The breech block (in a perfect world) should stop just short of that abutment, or just barely kiss it...while still ejecting & feeding...

You are trying to tailor your Luger to your cartridges...I don't use Fiocchi; I handload...and tailor my loads to my pistols...So in your case, yes, I would get a Wolff Springpack and try the weakest spring first...and see if I still get good ejection & feed...If not, move up to the next spring...and try again...etc...

Or you could do it the easy way, and mail your Luger to one of the real experts here to tune for you...(Mail the ammo you will be using too)...

Some here will say you can get an incremental 'tune' by clipping coils off a certain spring...For instance, if the toggle obviously doesn't go all the way back...and it stovepipes or doesn't feed...

I'm surprised none of the really knowledgeable people haven't jumped in here...I'm just a dummie... :D

I just gave a quick look into my Luger parts bin, and found three new Wolff recoil springs in the shrinkwrap...All three seem to be the same length and number of coils...Only difference is the wire diameter (which is good)...

36# - .056" dia
38# - .057" "
40# - .058" "

I thought they offered a "Pak" with all three, but mine are individual...

I haven't had to use them, as I handload...I select a bullet type & weight, and brand of powder...and then load the minimum amount of powder for that bullet...and increase it by one-half grain until the pistol ejects & feeds reliably...

Saves money on new springs... :)

Hi:

The frame on the right looks like the springs and ammo have been properly matched, as their has been no breach block slap. The Luger was not designed to absorb a regular pounding at this point, and as previously stated, this pounding is a major cause of mechanical failure with this design.

The Luger with the missing fin looks like it has taken quite a lot of pounding here and has failed. I agree with you that weak springs and/or too hot of ammo is the cause of this condition.

Original DWM military ammo for the 9mm, circa WWI, was 123 gr bullet at 1,076 fps, a rather middle of the road load by today's standards. The much vaulted Commercial Winchester white box is 115 grs at 1,190 fps (according to the Winchester web site) or 11% over original specs. The current U.S. Army Nato load is 121grs at 1,260 fps or 17% over original specs. I believe that regular use of the "hot stuff", even with springs in spec, will eventually lead to problems.

Now days when I'm shopping for a Luger, I'll try to examine this area for ususual wear. If it has taken a battering, I'll usually pass on the pistol and find one that hasn't.

I handload for all of my shooting with my Lugers, and handload to the original specs. These loads are also extremely accurate.

The Wolff #38 is the standard weight spring, but with "hot stuff", I'd try the 40 pounder.

Sieger

Try putting a piece of freezer or electical tape on the back of the frame where the rear toggle hits. If ammo and springs are in spec, it should leave a dent in the tape. If the tape is mutilated, either the spring is too weak or the ammo is too hot.

Hi:

Excellent advice!! This is low tech, but has been a standard test for years.

One additional thing. When there is breach block slap, you can really feel it in the web of your hand upon firing the pistol.

Sieger

SO, guys what is your final answer here. I use nothing but factory Fiocchi, (The Winchester is too high in price and ballistics are the same) Handloading ammo for me is just totally out of the question. Buy a 40 pound spring? ALL available .30 Luger I read is rated at 305 ft Ibs, and 1220 FPS. so.......... A spring is 7 dollars, big deal.

Hi guys,
if we want to compare the applied load that takes effect on a Luger during a shot, we must not compare the muzzle velocities of the bullets, but we must compare the momentum meaning muzzle velocity*bullet weight.
According to Newton's law the bullet's muzzle momentum causes the same but reverse momentum on the breech block and finally on the frame. That means that a light bullet with a high muzzle speed has an enomous energy but only a moderate momentum.
I regularly shoot Magtech 95gr ammunition with a muzzle speed of 1345fps in my shooters. Seems to be very hot, but the momentum is fairly soft.
Armin.

I have to add something here. The receiver is not slamming into the frame. It is the rear portion of the breechblock that is cushioned under spring pressure from the striker retainer pin. The striker retainer is what is hitting this area of the frame and is the abutment.

Frame fins crack in time, especially a weapon almost a century old, although one might say under normal operation these fins sustain no wear? But we can speculate that it is fact that this area of the frame takes a tremendous pounding from the returning toggle, multiply that by 8 rounds over and over , over a period of years and than decades and the steel just gets brittle.

What happens is, the movement of the toggle, down on the frame through the years moves all the molecules in the steel to a head, just like in the striker, (Why dry firing lugers is not a good idea) and it just gets old and brittle and breaks off as the molecules all shove into the corner of a fatigued piece of steel. . As far as the breechblock cracking? It is not the breechblock that is hitting this area put the striker retainer, and this is under spring tension and absorbs impact. As we know. The weapon is just old. I have seen many Shooter grade Lugers with these fins long broken off.

There is like 1/16th of an inch of space were the receiver stops short of slamming into the frame. It is my opinion that factory spring, unless miserably weak, should not be changed. iF THE GUN WORKS , LEAVE IT ALONE