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Old August 24, 2020, 06:13 PM   #1
hlangebro
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Lahti/Husqvarna m/40 broken receiver...

Greetings,
Yesterday at the range my Lahti/Husqvarna m40 broke and has a crack in the receiver...
One piece actually broke off and the crack had developed in the rear portion of the receiver...
I need to find a new receiver...Anyone got any leads?

thanks

Hakan Langebro
San Diego
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Old August 24, 2020, 06:38 PM   #2
SHR970
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Picture #1 shows the S/N for the reciever (aka the gun itself). You either find another gun or you find a gunsmith that can weld that piece back on and heat treat it so it "might" be functional again. Being that you are in S.D. Cali. you are going to be hard pressed to find a transferable Lahti anywhere in the state.

If I had a chance to buy a Lahti I would have one in my safe. I'm 2 hours north of you so I understand your dilemma.
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Old August 24, 2020, 06:53 PM   #3
RickB
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Is the failure of that part the reason the Swedes destroyed all of theirs?
If so, it's probably going to be very difficult to find a replacement.

Apex gun parts catalogs it, but they're out of stock.
Numrich also catalogs it, also out of stock.

If you don't mind; do you know when yours was made? Wartime guns were apparently made of inferior steel, but I wonder if that applies to post-war contracts, too?
Mine is a Danish police contract, from 1947, I think.
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Old August 25, 2020, 02:51 AM   #4
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Classic stress riser.

I appreciate your posting this. I got my Swedish Lahti out of the safe and the corners there are sharp. I used a 600 grit needlepoint diamond file to very carefully radius the corners at the point of failure on your pistol.

These pistols have kind of a reputation for cracking receivers. I imagine they all have stress risers in the spot where yours cracked which is a recipe for failure. Also, they have a bolt accelerator that is designed to drive the bolt back faster to insure reliable function in adverse conditions (especially extreme cold). It's been suggested that firing them in normal conditions with ammo on the hot end of the spectrum is not an especially good idea.

You may be able to find someone who is a very good welder to fix it--finding a new part will likely be difficult. You can watch the internet to see if someone decides to sell one. At one point, there were a lot of parts on the market for these and I suppose they didn't just disappear. Sooner or later something is likely to turn up.
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Old August 25, 2020, 06:46 AM   #5
highpower3006
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OP: I hate to say this, but your Lahti is toast and no amount of welding is going to make it safe to shoot. Maybe it can be patched together as a display piece, but I certainly would never feel safe shooting it.

And that is precisely the reason why I don't shoot my collectible firearms. Mismatched or really common guns, no problem. But guns like my high condition 1916 matching number C96 or my equally nice matching number 1916 dated LP08 are eye candy for me. Much like art, I enjoy looking at them, but I feel no desire to take them to the range.
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Old August 25, 2020, 10:24 PM   #6
RickB
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Quote:
It's been suggested that firing them in normal conditions with ammo on the hot end of the spectrum is not an especially good idea.
Mine won't cycle normal-pressure 9mm with the accelerator removed, so, it's either shoot them with the accelerator in place, or +P to cycle without it (maybe).
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Old August 25, 2020, 10:57 PM   #7
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I'd go with the normal pressure and maybe stick with the lighter bullet loadings then.

Results without the accelerator are mixed. I've seen some folks say they work fine without them while some, like you, report that their pistol won't cycle with the accelerator removed. I don't know what makes the difference--it's puzzling especially since some of the later iterations of the design didn't even have the accelerators.

Pressure is probably what stresses the locking mechanism, so I wouldn't go with +P even without the accelerator. The OP's pistol cracked where the locking block bears against the slide and more pressure would put more stress in that area.

Higher muzzle momentum will result in higher slide velocity and that will stress the slide in the vicinity of the accelerator which is the other area prone to cracking. Going with mild practice loadings with lighter bullets should keep the slide velocity down and cut down on slide stress.

Also, check frequently for cracks. If you catch them very early, it might be possible to fix them with some very good welding.
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Old August 27, 2020, 11:04 PM   #8
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Quote:
Pressure is probably what stresses the locking mechanism
It looks like the high stress would be on the forward surfaces and not the rear ones, perhaps when the slide comes back into battery the lugs slap the rear pieces hard?
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Old August 28, 2020, 12:10 AM   #9
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The bolt is held closed (forward) against the firing pressure by the locking block. That places a rearward force on the locking block which, in turn, bears against the slide where the crack formed.

Recoil drives the entire slide/bolt/barrel assembly backwards as a single unit until the unlocking mechanism raises the locking block and allows the bolt to move back independently of the slide & barrel.

So pressure will place stress on the slide where the crack formed. I suppose recoil does too. The forward area around the accelerator shouldn't be directly stressed by pressure--slide velocity/recoil is going to be the stressor there.
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Old August 28, 2020, 01:53 AM   #10
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Ah yes, it doesn't have a slide like most pistols, the breechblock is held forward by blocks at the rear.
I'm amazed at the many ways I can be wrong!
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Old August 28, 2020, 02:22 AM   #11
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It is an interesting and unusual design. Being able to handle one and play around with it helps a lot in understanding how it works. Having an independent bolt isn't something you see very often in recoil-operated centerfire autopistols.
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