Breech block not closing

[Olle]

Got a problem that I hope is easily fixed: My "mixmaster" Luger won't go into battery when I load it or shoot it. It ejects, cycles and feeds fine (using UMC 115 grain) and the barrel extension goes all the way back, but the breech block stops about 1/8" open. Once i push the toggle down, it will shoot just fine but will do the same thing again. It seems like it just doesn't have enough "oomph" to go all the way.

This last fraction of an inch seems to be a weak spot in the design, the final closing appears to be more a matter of inertia than spring force so I'm thinking that it's dragging somewhere. A bullet will drop into the chamber without any problems and it will close fine without being loaded, so I'm thinking that the problem could be either in the mag or the ammo. It's just losing momentum somehow. Any ideas?

[alanint]

Look closely at your pistol's frame to see if the rails up front are pinched in. This is the typical place that people put Luger frames into vices, for some reason and they may have overtightened in this area.

Does the entire upper receiver/cannon slide easely off the lower?

[mrerick]

Also check to see that the extractor's spring and the well it fits into is clean. It could be encountering resistance as the extractor climbs over the cartridge edge.

It could also be a fitting issue relating to the shape and finish edge of the extractor.
Marc

[Olle]

Originally Posted by alanint

Look closely at your pistol's frame to see if the rails up front are pinched in. This is the typical place that people put Luger frames into vices, for some reason and they may have overtightened in this area.

Does the entire upper receiver/cannon slide easely off the lower?

Yep, everything slides really easy when you disassemble and reassemble so I don't thing anything is there is out of whack. The action works perfectly fine when working it without ammo.

Originally Posted by mrerick

Also check to see that the extractor's spring and the well it fits into is clean. It could be encountering resistance as the extractor climbs over the cartridge edge.

It could also be a fitting issue relating to the shape and finish edge of the extractor.
Marc

That sounds like something I need to check. While I was shooting, I got the impression that it didn't have quite enough inertia to **** the firing pin. Once the action stops, the cartridge is already held by the extractor and it's just a matter of giving the toggle a push to **** and close the action. It the extractor is dirty ot bent out of shape, it could lose momentum right there and stop after the cartridge is seated on the breech face.

Again, the action works properly when working it unloaded, so whatever this is must be something happening around the bullet (i.e. not the mag, not the rails etc).

By the way, it would be nice if the moderators would take the word "****" off of the list of words to auto delete. It's kind of useful on a gun forum.

[alanint]

If the problem disappears when there is no ammo in the chamber, it is undoubtedly your extractor. Remove it by pressing down slightly on it and pushing the pin out. The well it sits in is rather deep and can acumulate a good amount of debris. Make sure this recess is completely clean and that the extractor and spring show no damage or excessive wear.
If this area is clean and in good order, the next thing I would look at is your mainspring.

[Olle]

I have been wrong before, but I strongly believe it's the extractor. The toggle snaps shut and with good force when you work it dry (with or without the magazine inserted), so I can't imagine that anything is binding. You'll only see the problem when you add a cartridge to the equation.

The mainspring is in good order, and it has already moved the slide extension to its forward position when the toggle stops. In other words, it happens right as the firing pin is getting cocked. The toggle spring applies very little force at that point, so that's why I assume that most of the closing action (i.e for the last 1/4"-1/8" or so) is accomplished by inertia. Anything that drags or binds at that point can easily cause it to stop, as there's little spring force left to help it forward.

I also noticed that the primers had unusually deep dents, so another theory is that the firing pin spring is too strong. I'll check the extractor first though, it's easy enough to do.

[alanint]

A good point. If someone has thrown a replacement firing pin spring in there that is not appropriate, (too strong) for the gun, the force required to set the FP upon closure could certainly be causing this.
It may be right on a mechanical tipping point, where it will set the FP when not trying to pick up and chamber a bullet but not when tasked with this extra work.

[Olle]

Originally Posted by Rick W.

Could it possibly be a ammo dimensional thing? I was talking with some folks about their 9mm's that were shooting factory ammo, two guys had factory 9mm ammo that would chamber in some auto's and other auto's not. Both instances were with a bulk box of factory ammo. Not all the cartridges were so affected, just some from each box.

The ammo should be able to insert fully and release with just a tip of the barreled receiver loose and no toggle etc; ie fall in, fall out without manual assistance.

I am a reloader only, but I gotten into the habit of running all my reloaded ammo thru the loose barreled receiver.

Sounds like you are homing in on it..............

The chamber is fine, a bullet will drop right in just like you describe it. It actually seems to be on the loose side, so I'm going to check the casings later to make sure they're not bulging. There could be something about the casings the pistol doesn't like though, the rim on the UMC has pretty square edges and you can see pronounced scratches where the extractor has been sliding over it. It's very difficult to tell what's going on here. If I understand the function correctly, the extractor will slide over the rim after the bullet is seated in the chamber. The breech blocks stops before that, but that could be because it actually bounces back from the firing pin pressure. You would need a high speed camera to catch that.

In any case, I checked the extractor and there was some gunk under the claw, but I'd still say that the whole assembly was very clean. I polished the extractor a bit just for good measure while I had it out, cleaned and lubed everything etc. I also found that the breech block is pretty tight in the rails, so I polished it a bit. That actually seemed to slick it up quite a bit, but there's still just about zero play side to side.

Next step is to dig deeper in my safe and see if I can find ammo with a taper on the rim. I would imagine that this would work much better in a Luger, so any tips on that would be appreciated. I might also hone the breech block a bit, it's not binding or anything but the lack of side play bothers me and it could sure be slicker.

Edit: This may be unorthodox, but has anyone tried lapping compound to fit the breech block on a Luger (i.e. coat the mating areas with lapping compound, and work them back and forth)? I do it on other auto pistols now and then, but the Luger is kind of uncharted territory to me so I thought I better ask.

[rhuff]

I own a 1921 Commercial Luger that is pretty finicky about what ammo that it will function correctly with. I found that 115gr PMC FMJ ammo works great. It is very reasonably priced also. You might give it a try....just a thought.

[mrerick]

Olle, The fit of the toggle train in the receiver is generally quite close, but smooth. The tolerances were low and they were hand fit at the factory.

As mentioned in an earlier post, it is possible that someone inadvertently "adjusted" the receiver tighter by clamping it in a vise. It's worth a look at the barrel to receiver witness mark (on the bottom) to see if it lines up perfectly and if it's ever been disturbed by someone re-mounting the barrel.

The toggle train movement should be very smooth, and not feel like there is resistance as it completes going into battery. If it closes smoothly without a cartridge in the chamber, but encounters resistance with one in the chamber (even a fired case) then look more to the extractor as it climbs over the cartridge edge.

The use of lapping compound to polish the fit is a question for the more experienced Luger gunsmiths...

Marc

[Olle]

Shot it again today, and it was still doing it's thing. I took the whole top end apart completely so I could check the breech block in the upper, without any other parts dragging on it. I also checked it with feeler gauges, and found that the rails on the breech block were a tad too wide and dragging slightly on the bottom of the grooves in the upper. I polished this to fit, and polished some more on the rails. After that, the breech block would fall right in without resistance, so any problem from now on must be located somewhere else. The ejector felt a bit gritty, so I polished the groove just for good measure.

Now it will at least shut close on an empty casing inserted in the chamber. I'll try it again tomorrow, will also get some Winchester "white box" to see if it makes a difference.

[Olle]

Ok, time for an update: I tried some white box Winchester, and it was close but no cigar. The toggle will almost close and the cartridge will be seated against the breech face, but it still leaves about 1/16" to go. I hand fed the cartridges to study their way to the chamber, and found that it was a bit of a rough and "wiggly" path. I don't really want to polish or reshape the feed ramp, but that might be what needs to be done. I'd probably be better off trying a new recoil spring first.

[alanint]

Another possibility is to take some Flitz or other mild abrasive and completely polish the chamber area by putting a cleaning patch soaked in the abrasive onto a brass brush and the rod end on a electric drill. This will not damage the metal and may give you just enough of an advantage to solve this.

[rhuff]

I, personally, would not change the feed ramp profile in any way, shape or form. I do polish the feed ramps(frame and barrel) on my shooters, and it definitely helps the feeding process. I start with a 320-400 grit paper/cloth on a wood dowel moving fore to aft to get the machine marks(frequently bad horizontal gouges from a dull tool) lessened/gone. Then I use a felt bob on my dremel at low speed with jewelers rouge(red) for the final polishing. I do not change the ramp profile at all, only clean up the rough machine work. If the feed ramp is really rough, it may be slowing the cartridge feeding process down enough that the main spring can not over come it. I would FIRST try a new mainspring, and then go from there if you need to.

[Olle]

Yeah, I believe the spring is the next step. The chamber is smooth and almost on the large side (like I said above, a cartridge will slide in an out by its own weight) and the problem seems to be occuring long before it seats in the chamber. I have done the "fingernail test" on the feed ramp without finding any burrs.

The movement seems to be rougher right as the cartridge exits the magazine, but this is what I see when I'm slowly lowering the toggle by hand so it's really not representative to what happens when you shoot. Its not any worse than I have seen in other pistols, and I hate to do irreversible things like feed ramp jobs anyway. Some more spring tension should hopefully do the trick.

[rhuff]

Sounds like a good plan. Keep us informed as to progress.

[Olle]

This is taking way too long, but that's the way it goes when you have too many projects going on.... Installed a new Wolff main spring this evening, together with the firing pin spring that came with it. I read up on it before I started, but it was actually easier to change the mainspring than I have seen described in some instructions. Maybe my long fingers helped, but it was just a matter of sticking a punch through the eye and pulling a bit. The proof will be in the proverbial pudding, will hopefully test fire tomorrow. Stay tuned.

[rhuff]

I wish you good luck with your new springs!! Let us know.

[Terry Tiell]

I know when mine had its original main spring it would sometimes hang up the same way you describe yours doing. I replaced all the springs in the gun and polished the feed ramp to a chrome like finish and am able to run as much ammo thru it as I want to with zero problems. After I spent a week fitting and polishing everything inside I took it the range and ran 300 rounds thru it without one single problem. Good luck Olle I hope you get your working as well as mine.

[Olle]

The new spring gave it enough force to close, but now I have two other problems:

It's really hard to chamber a round when the mag is fully loaded. The notch for the hold-open seems to hang on the rim on the top cartridge, and it takes a good yank to get the breech block beyond that point. Could be that the feed lips need to be adjusted a bit to get the cartridge to sit lower, so the next step will be to try it with an aftermarket mag and see if it works better.

It fed correctly with just a few rounds in the mag, but the firing pin failed to **** several times. Not sure what's up with that, the sear engages just fine when i work the action by hand.

Back to the drawing board again...