K31, a love story

Apparently K31's are pretty impressive themselves on the rare occaision they let go (or to be more precise, are let go by handloaders)


...and also FWIW, the guy was bloodied but not seriously injured (parts went up, not back, and the bolt remained in battery under a double-load of 4400! )

I saw earlier in the thread it said that K31's can't fire out of battery. That's not quite true, as I recall from the SwissRifles website. The camming pin on the operating handle rides in the bolt sleeve groove that closes the bolt when full forward. But it also acts as a stop for the firing pin if it isn't all the way forward (and the sleeve is not fully rotated). When a shoulder on the firing pin smacks the camming pin, it pushes it forward, and rotates the bolt-sleeve into full battery, and leaves only a small primer dent as too much energy is wasted on the bolt movement.


If that little protrusion on the operating rod becomes broken (as it is sometimes known to do, being the most strained part of the very strong bolt assembly) due to metal fatigue or over-zealous bolt use (i.e. the Mosin boot-heel treatment), it can no longer perform its critical function. Normally when it breaks the issue is immediately apparent; the handle won't push the bolt, and the little force required to work the handle goes to zero

However:
IF that little camming piece breaks free of the gun just as a round is chambered, it is possible (though highly unlikely) that the bolt handle will go (almost) all the way forward, but the bolt sleeve won't turn--and the firing pin interruptor is no longer there. Kaboom will certaintly result at that point because I don't think there is a trigger-block based on bolt rotation, only one based on bolt-forward position. IF the clueless shooter doesn't realize their bolt hasn't gone all the way forward and the sleeve hasn't rotated.

Anyway, the gist of what I'm saying is the K31's out of battery safety is redundant, but defeatable. A better system would have been to use an interruptor lug on the bolt itself to stop the firing pin, instead of putting it on a separate part that may or may not be determining the bolt's rotation. The K31 is far-and-away the safest of straight-pulls, though. The Ross's bolt can be reassembled in such a way that everything works properly--except the bolt won't rotate before the trigger is pulled. That rifle is the sole source of the distrust for straight-pull rifles (even old M95's are pretty robust).

For sure the K31 doesn't handle overpressure as well as modern designs, so glasses are a must.

TCB

Very good and informative information barnbwt!

I just learned some new stuff there.

I've had mine since I was 16 or 17, and never loved any less.

Yeah, I was paranoid when I first bought the K31s, and I wanted to be darned sure I knew how they kept the bolt outta my face

The sleeve-camming makes the K31 a tiny bit less fail-proof than the Steyr M95, which I believe simply rams the front of the locking lugs against the back of the barrel (this causes the bolt head to snap down against the bolt-body, rotating on helical cams inside the bolt body as it does so). I think that unless the interior bolt-cam surfaces are completely sheared (shorn?) off, the gun cannot fire out of battery. even in that case, the debris would probably inhibit function. I think there's also a keyway in the bolt head that only allows the firing pin through when it's in the proper orientation. And finally the trigger can only engage the bolt-mounted sear when it is in the full forward position.

TCB

I took about two weeks for the order to be processed the last order I placed at Samco.

Anyone have experience with stripper's?

I read that the magazine's were not meant for holding cartridges outside the gun, so no need to buy a extra magazine.

I read the cardboard strippers will eventually break. Are they worth it?

I also read that Mosin-Nagant stripper clips fit just fine, but haven't tried. Anyone tried it?

I know that the swiss decided not to use conventional stripper's, and that swissbianco was talking back in October about reproducing them. Is there any information on that?

Buck Kramer -
You seem to an expert on K31's. I was wanting to get some spare parts, in case, decades down the line, something breaks. If there's anything the last few months shows(303, 8mm ammo for example), milsurp thing's won't last forever.
What parts should I get?
And also, I noticed on Graf's that there are different headspace markings on bolt cylinder's. I read I need match them to have the same number as the bolt's. Can you describe that a bit, why that is, and where to check? I am a real newbie on this.

Got my K31 from AIM in 2004 - about $100.

OK, I'll admit it, I've never shot it! Reading this, I feel like a super failure now.
I should at least look under the buttplate.

OT - Above someone mentioned the 8mm Persion ammo "blowing up" a rifle. My impression is that old ammo can only get weaker (hangfires, squibs, failure to fire, etc), not stronger. I mean, the gunpowder can't become more potent, right? So, what caused that?

Noooooooo...

Old ammo can become downright MALIGNANT.

If in doubt pull the projectile and look at the powder. If it's clumped, or changed color, it's bad news!!!!

(Keep in mind it has to be DAMN old, or exposed to really nasty conditions, to go that south.)

Ammo properly stored in a cool dry place will last ~50 years .. Ammo environmentally sealed in a can will probably last until that can rusts through, or if intact, until archeologists dig it up some day. Provided it's kept cool.

That 1920's persian ammo is almost 100 years old and it was stored in hot climates... not good for it.

There was a study I saw posted once where ammo was stored in a trunk for 1 year down south (exposed to temps ~150F daily) and the pressure when fired was about 150% of normal.

K31 safety versus Mannlicher M95 or Ross M10 concentrates on a very unlikely circumstance of the operating rod cam failing at just the wrong time. Having owned examples of all three of these action types, I'd like to bring up a more serious design flaw. In case of a pierced primer, the K31 stays securely locked, the bolt is pretty well vented and the worst that can happen is the firing pin getting pushed back.

In the case of the M95 and the M10, the bolthead carries cams that engage matching surfaces on the inside of the bolt body. These cams rotate the bolthead to lock and unlock the action. In case of a pierced primer, gas follows the firing pin past the spring and into the space inside the bolt body. If you know how an AR 15 works, you can see what comes next: the gas expands into the bolt body, forcing it to move backward and rotating the bolthead into the unlocked condition. The designers knew about this problem and tried to compensate by venting the bolt body. In the case of the Ross, the vents in the bottom of the bolt body are huge.

So, problem solved? Well, at least one anecdote says not. When the .280 Ross cartridge was the new hottest thing on the block, one US ammo maker decided to tool up and make the cartridge. They put a sporter M10 rifle in a test fixture and started working up some loads. During one string of experimental loads, on the third shot from the magazine the bolt ejected from the rifle forcefully enough to break the bolt-stop and leave the gun. Note that the bolt had not been removed from the gun during this string, so there was no possibility of the bolthead being flipped into the unlocked position. The gun was functioning normally, until the bolt unlocked itself and left the gun. The project of developing for the cartridge was abandoned right then.

Despite the massive receiver ring and multiple lugs on the Ross M10 action, I'd still feel a lot safer behind a K31 in the case of an ammo 'malfunction'

IMHO

Good point about the pierced primers (yet another failure mechanism to be designed around). Because the gas can't impinge on the operating handle of the K31, it is indeed safer in that circumstance. Makes me feel even better about rechambering my Steyr M95 to 50 Alaskan, which operates at near half the pressure of the original chambering--much less chance of primer failure.

If the K31 had been designed to have two camming pins driving the bolt-turn I'd like the design a lot more, because it would have redundancy for that (somewhat) failure prone critical part, and would also be ambidextrous . I'd be much less worried about forcefully working the bolt on a stuck case, as well.

TCB

Swiss with nikon 6-18

More eye candy, with this scope the rifle will stack bullets at 200 yds. Of course it would anyway, but my glasses don't mix well with irons...

Nikon 6-18 Buckmaster and 150 GMXs at 2815 fps. Does a great job on Antelope at any range.

has anybody bought a repro stock and handguard set from Boyds? I'm interested in making a "nice" set to use and leave the originals in the safe. I doubt the K31 will increase in value over time much beyond current prices but you never know...

I did not get the repro from Boyd's but I did get the monte carlo for a K31 I had with a broken stock. The Monte Carlo needed a good bit of chisel and rasp work to get the fit just perfect, but overall I really like the quality of the stock, and the speed with which I recieved it after ordering.