The bolt didn't crack, and the barrel/chamber didn't crack, and the bolt lugs are still there, so it appears that gas escaping from a blown case blew the receiver apart. The part that blew out is not a stressed part in the firing process, so it doesn't appear to be from a weak critical part....ie chamber, bolt lugs, receiver lugs. I had no idea that a ruptured case would do that much damage, but I'm not too familiar with what is built into the design to channel gas from a blown case?
K-31 Ka-boom
- Thread starter slug
- Start date
The bolt didn't crack, and the barrel/chamber didn't crack, and the bolt lugs are still there, so it appears that gas escaping from a blown case blew the receiver apart. The part that blew out is not a stressed part in the firing process, so it doesn't appear to be from a weak critical part....ie chamber, bolt lugs, receiver lugs. I had no idea that a ruptured case would do that much damage, but I'm not too familiar with what is built into the design to channel gas from a blown case?
Years ago, a friend and I duplicated a "PO Ackley test". We recahmbered a beater, ground mum, $3 ea, arisaka m38 to 30-06. Very rusty bore.
Undrestand, the bore diameter was still the original 6.5 diameter. The only other modification was to open the bolt face a bit. The rifle was then securely tied down to a truck tire.
We then loaded up a 30-06 cartridge with a 180gr kksp and as much 2400 as we could squeeze into the case. Should be a decent recipe for disaster, WRONG.
There was a huge muzzle blast, flame and smoke comeing out of the vent and around the bolt and the stock was cracked at the wrist.
The bolt was impossible to open by hand and need to be whacked open with a length of 2x4. The cartridge case had flowed into every nook and cranny on the bolt and failed under the extractor. Other than that, nothing.
Cleaned up the bolt and did it again, this time with a 220g roundnose bullet. Really big flash/bang this time. Mag well and floorplate had disappeared, stock was shattered barrel was bulged and the bolts was frozen firmly in place, with visible brass flowing out of the vent hole and under the bolt.
We broke off the handle trying to open the action. So we screwed the bbl from the receiver to take it apart. Took a bit of work to get the "fireformed" brass out of the lugs and receiver but when it did come out, we had a surprise.
There was nothing wrong with the bolt or receiver, other than what we did to get it apart. All of the damage was caused by catastrophic cartridge case failure. The bore was clear as well.
This rifle action should have exploded. It didn't. In fact, this action and bolt were cleaned up, rebarreled, chambered in 257 Roberts and is still in use today, takeing its fair share of coyotes and deer.
This same test was carried out by Ackley a long time ago to determine the strengths of various milsurp actions and pretty much had identical results.
I've also had an M38 Swede blow the same way as that K31 did. The load was safe as far as specs went, but the cases, being extremely hard to come by in the late 70s, were made up from sized down 308Win, which left a very short but acceptable neck. Then we found out about the Boer mauser Kabooms with 7.65 mauser cases reformed and reloaded to 7x57. The short necks were considered the blame.
I think the K31 rifles are made from pretty decent steel and as stated by your gunsmith there must have been a metal fault. Your charge, may not have been doubled, but may have been much less, creating a detonation, rather than a controlled burn.
bearhunter
Undrestand, the bore diameter was still the original 6.5 diameter. The only other modification was to open the bolt face a bit. The rifle was then securely tied down to a truck tire.
We then loaded up a 30-06 cartridge with a 180gr kksp and as much 2400 as we could squeeze into the case. Should be a decent recipe for disaster, WRONG.
There was a huge muzzle blast, flame and smoke comeing out of the vent and around the bolt and the stock was cracked at the wrist.
The bolt was impossible to open by hand and need to be whacked open with a length of 2x4. The cartridge case had flowed into every nook and cranny on the bolt and failed under the extractor. Other than that, nothing.
Cleaned up the bolt and did it again, this time with a 220g roundnose bullet. Really big flash/bang this time. Mag well and floorplate had disappeared, stock was shattered barrel was bulged and the bolts was frozen firmly in place, with visible brass flowing out of the vent hole and under the bolt.
We broke off the handle trying to open the action. So we screwed the bbl from the receiver to take it apart. Took a bit of work to get the "fireformed" brass out of the lugs and receiver but when it did come out, we had a surprise.
There was nothing wrong with the bolt or receiver, other than what we did to get it apart. All of the damage was caused by catastrophic cartridge case failure. The bore was clear as well.
This rifle action should have exploded. It didn't. In fact, this action and bolt were cleaned up, rebarreled, chambered in 257 Roberts and is still in use today, takeing its fair share of coyotes and deer.
This same test was carried out by Ackley a long time ago to determine the strengths of various milsurp actions and pretty much had identical results.
I've also had an M38 Swede blow the same way as that K31 did. The load was safe as far as specs went, but the cases, being extremely hard to come by in the late 70s, were made up from sized down 308Win, which left a very short but acceptable neck. Then we found out about the Boer mauser Kabooms with 7.65 mauser cases reformed and reloaded to 7x57. The short necks were considered the blame.
I think the K31 rifles are made from pretty decent steel and as stated by your gunsmith there must have been a metal fault. Your charge, may not have been doubled, but may have been much less, creating a detonation, rather than a controlled burn.
bearhunter
And once again, I will point out these guns are NOT battle tested 
That receiver looks like the pics in Hatcher's notebook of blown-up M1903's that had improper heat treatment making the steel too brittle. That failure is too crystaline to indicate failure due to plastic deformation as we would see in a modern gun, or even most guns made after 1918. It looks to me like the steel is martensitic. It should not be. The grain should look like a mix of austentitic and pearlitic steel that underwent plastic failure in a typical blowup.
Glad to hear you are OK.
That receiver looks like the pics in Hatcher's notebook of blown-up M1903's that had improper heat treatment making the steel too brittle. That failure is too crystaline to indicate failure due to plastic deformation as we would see in a modern gun, or even most guns made after 1918. It looks to me like the steel is martensitic. It should not be. The grain should look like a mix of austentitic and pearlitic steel that underwent plastic failure in a typical blowup.
Glad to hear you are OK.
Yeah, what I said in post 2. Claven just knows what he's talking about.
Translated (dummed down)...
the busted up reciever looks like when cheap white metal breaks...
If it was good metal it would look more bent and torn than shattered
maybe I wont try shootin my swissy....
I was gonna suggest that....beat me to it
Heck of a way to deactivate a rifle
GLAD YOU'RE OK SLUG!
Don't strip her for parts
Impress your friends and make her a wall hanger
By the way
I don't like the way that opened up receiver metal looks
Boys its time to rockwell test your K31 receivers.
GLAD YOU'RE OK SLUG!
Don't strip her for parts
Impress your friends and make her a wall hanger
By the way
I don't like the way that opened up receiver metal looks
Boys its time to rockwell test your K31 receivers.
Slug
Is the operating rod still in one piece or is the lug that fits into the bolt broken off like this:
http://img.photobucket.com/albums/0703/guisan/album 4/brokenbolt.jpg
Does your receiver and/or operating rod have a CN(Chrome Nickel) or a CM(Chrome Moly) stamped on them?
Where your cases necks on the short side? which brass did you use?
PS. Glad to see you're ok.
Is the operating rod still in one piece or is the lug that fits into the bolt broken off like this:
http://img.photobucket.com/albums/0703/guisan/album 4/brokenbolt.jpg
Does your receiver and/or operating rod have a CN(Chrome Nickel) or a CM(Chrome Moly) stamped on them?
Where your cases necks on the short side? which brass did you use?
PS. Glad to see you're ok.
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X2
I personally feel the problem is, 22grns of a magnum pistol powder in a rifle case with lots of air in it, a recipe for a detonation.
But, if any of you are worried about the soundness of your K31 rifle, Andy or myself will be more then happy to take them off your hands, free of charge
I can see this story evolve in the next few years. Sooner or later, you'll be at the range, and you'll hear guys chatting...
"Yeah, like, man, I know this guy, who knew a guy who met a dude once, had a K-31, like the most dangerous piece of metal E-VER! He just looked at the rifle, no rounds in it, I swear! And the rifle - get this - EXPLODED!
- Man, I didn't know rifles could explode on their own!
- And that's nothing. When it exploded, the front sight blade flew off and cut the guy's left leg off!!!"
When a case head fails the gas gets loose and takes bits and pieces with it.
My guess is a double charge of 2400 and a failed case head. Some rifles handle a gas excursion better than others. The M98 is one of the better ones.
When loading, it is good practce to load all the cases and then scan the loading block, looking for empty cases and cases that look differently charged than the others. This is critical when loading ammo where a double charge is possible.
My guess is a double charge of 2400 and a failed case head. Some rifles handle a gas excursion better than others. The M98 is one of the better ones.
When loading, it is good practce to load all the cases and then scan the loading block, looking for empty cases and cases that look differently charged than the others. This is critical when loading ammo where a double charge is possible.
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sillymike
CGN Ultra frequent flyer
X2
But, if any of you are worried about the soundness of your K31 rifle, Andy or myself will be more then happy to take them off your hands, free of charge
If anybody wants to save on shipping, I'll gladly collect any un-wanted K31 in the Montreal area
Free of charge again!(Glad your OK!)
I should point out that Rockwell testing won't identify a brittle receiver. Both Martensitic steel (like the above looking gun) and austentitic steel (preferred) are usually surface hard, probalby on the order of 50+ RC. This is because austentitic military arms were, after 1918 or so, usually given a 2-stage heat treatment process allowing for an elastic core that fails plastically surrounded by a very hard skin for wear characteristics, whereas Martensitic steel receivers are hard all the way through.
This is why the only way to ID a dangerous M1903 is be serial number. The same will hold true for K31's I would venture to guess.
Not really. The rifle is early 1952 production. The first 200 K31s were used up as cutaways to show how it works to the troops. They should have had the surface hardening procedure down pat by that the time actual production started. Carbide drills are needed to go through the surface hardening on the recievers. Quite possible some improperly hardened ones got by QC.
I like the theory proposed by Delloro on the Swissrifles Message Forum.
(10/27/08 16:25:20)
"an oversized bullet can cause an overside neck diameter, raising pressures. it's not the bullet being forced down the bore, which doesn't take much pressure. is the fact that the bullet is bound in the neck by the chamber, acting like a bore obstruction."
http://theswissriflesdotcommessageboard.yuku.com/topic/5519?page=1
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Our Swiss gunsmith looked at this, he has only ever seen something similar once, and it was because soemone wanted to load the 7.5 round down to subsonic. So, a similar situation with a small charge in a large case.
FWIW the Swiss shoot their rifles alot with their military ammo. Probably more than most countries. There are no reports of these types of failures with service ammo, so one can only assume that the problem does not lie in the rifle but rather the ammo. If you shoot GP11 ammo your rifle will shoot many 10s of 1000s of rounds safely.
FWIW the Swiss shoot their rifles alot with their military ammo. Probably more than most countries. There are no reports of these types of failures with service ammo, so one can only assume that the problem does not lie in the rifle but rather the ammo. If you shoot GP11 ammo your rifle will shoot many 10s of 1000s of rounds safely.
Thanks Claven for clarification. My concern was through hardening VS case hardening. You're absolutely correct, rockwell is not the appropriate assessment tool to determine that.
I think you guys have this one down regarding the use of utilizing a fast burning powder behind a seriously oversized hard cast projectile. Regardless I'm not impressed the gas system did not divert the energy on this failure.
Having said that I am very ignorant of this Swiss rifle platform. The end result of this dialogue will determine if I ever own K31
I think you guys have this one down regarding the use of utilizing a fast burning powder behind a seriously oversized hard cast projectile. Regardless I'm not impressed the gas system did not divert the energy on this failure.
Having said that I am very ignorant of this Swiss rifle platform. The end result of this dialogue will determine if I ever own K31
