K-31 Ka-boom

[slug]

A few weeks back one of my K-31 Schmidt-Rubins blew up on me. The top of the receiver ring blew off and the stock was shattered. Fortunately, I had on glasses and muffs.
I may have used a double charge of 2400 powder, but a gunsmith friend doesn't think that might have done it. He noticed that the receiver ring was darker near the front than the rear areas of the fracture which are brighter. He thought that there was a previous fracture that weakened things.
I was using water-quenched, hard, as-cast bullets of .314 diameter which is a bit large for the 7.5 mm. cartridge, which may have contributed to the failure.
Photos of my blood-drenched physiognomy are unavailable.
It looks like I'll have a bunch of spare parts for sale on eBay shortly.

http://img.photobucket.com/albums/v517/slug303/DSC_0099.jpg

http://img.photobucket.com/albums/v517/slug303/DSC_0100.jpg

[45nut]

Ouch!

[jack19512]

WOW, that really sucks. I am by no means an expert on this subject but do think something went bad wrong in the reloading process. Any reason you were using .314 diameter bullets? What charge of 2400 were you suppose to be using?

[Ricochet]

Ruptured case head let gas into the receiver ring?

Sad that the rifle got blown up. Glad you're not seriously hurt!

[Bullshop]

`I dont know how you can even get a .314" diameter boolit to chamber. I use Win 284 brass necked up and I cant get a .310" to chamber.
I have not seen one of these go over .308" groove diameter.
Bummer! Looks like it was a clean rifle. Glad your OK though.
BIC/BS

[ez4545]

WOWZA, Thank the Lord you weren't injured worse!

Bill

[MtGun44]

Glad you were not seriously hurt, a shame to lose a fine rifle.

I'm with bullshop. No possible way to chamber a .314 in any
of my 3 K31s, I wonder how it was done. Also, hard cast .314 down
a .308 barrel (have not seen one over .308 either, mine has a .298
or so bore diam, too, can't find a bore rider with a nose small enough).

Have you shot this before or was this the first? May have pushed
the boolit into the case, increasing pressures, or the boolit so large
that the case could not open up at all to release it.

More info, please. Dimensions do not seem to add up.

Bill

[Buckshot]

..................Certainly thankfull that you are okay, and those around you weren't hurt. Does look like some pretty good pressure was happening. Lots of vaporized brass appears to be plated on those closeby parts :-)

................Buckshot

[madsenshooter]

I noticed that the bolt didn't appear to be all the way in battery in the above destroyed rifle. That could have occurred during or after the explosion, but it piqued my curiosity. I had a B&M 311169 bullet sitting in front of me, and a Graf's 7.5x55 case. The two of them got slowly together until the serial # on my bolt was in approximately the same position as that of the wrecked rifle. The firing pin wouldn't fall all the way on my rifle. But I thought I'd post this pic. The front driving band measures .313, forward of the shaved area mics .3065. Notice the burnishing on the case neck, no doubt another .001" would have made more of it. Slug didn't give us the design of his bullet, but the throat would have shaved off .0075" of the bullet, and depending on his case, the neck probably didn't have any room to expand. These 2 factors, in combination with a quick powder, probably produced enough of a pressure spike to do the rifle in. As others have said, thankfully only the rifle. Don't get gun shy slug!

[Bret4207]

Yeeeow! Isn't thata brass coloring I see around the bolt head? I think the case let go based on the coloration and the damage. Could well have been an over charge. Too bad. Hope you didn't get hurt.

[Shiloh]

...I was using water-quenched, hard, as-cast bullets of .314 diameter which is a bit large for the 7.5 mm. cartridge, which may have contributed to the failure.


Why were you using a WAY oversized boolit??

Depending on the actual bore diameter of the Schmidt-Rubin, .314 boolit puts is .016 to .018
oversize. This seems extreme to me.

Shiloh :castmine:

[sundog]

Looks to me as though it is out of battery, too. Serial number should be straight up. Question is, was it fired that way, or even possible to fire that way. I hope nothing other than the gun and your pride got hurt.

[Doug Bowser]

As some other posters have said, the over-sized bullet caused the bullet to be pinched by the neck and raise pressure. I had a friend that made some 7.65x54 Mauser ammo from USGI .30-06 brass. Even though his load was not hot, he could not open the bolt after firing the first shot. Always check the loaded neck diameter when you reload.

Doug Bowser

[EMC45]

My Swiss slugs at .308 and it has a very short/tight throat. Hard to find a lot of bullets that will fit.

[JSH]

First off, glad no one was hurt.
I too am sorry to see such a fine rifle expire like this. I had always wondered how one would hold up to such an incident.
As far as it not being in battery all the way. I am no engineer, the 6 I have fooled with will NOT fire if the lugs are not fully locked. Pictures are hard to tell, but if going by serial #, hard to tell how much of the action is distorted or if some one tried to beat it open.

Not to step on anyones toes, but looks as a classic job of bad reloading habits.
The 7.5's I have had to slap the bolt forward on, were all issues with the shoulder.
There is enough info and links on this site, on this subject, that this should never have happened, over sized boolit.

BTW, I have made 7.65x54 from milsurp 06 brass. After sizing and trimming, neck wall thickness was to much. I turned a few then reamed the rest, donut problem went away with reaming.

Another lesson we should all take notice of. Mistakes do happen. One can never be to careful.
Jeff

[Ivantherussian03]

A good learning opportunity thanks for sharing. Time to step back and re-evaluate.

[NoDakJak]

I suffered through a somewhat similar event a year ago. Even worse than the loss of a good rifle is that it screws with your mind. Problems that it left me were a severe flinch, trigger jerking and unconsiously closing my eyes when squeezing the trigger. It has been a battle but I am finally getting over it but I still have to be very deliberate and concentrate when squeezing that trigger. Good luck. Neil

[jack19512]

Would have been nice if slug had come back and satisfied some of our curiosity. Sure would have liked to find out why he was using a .314 boolit in the K31 and what charge of 2400 he was using.

[madsenshooter]

I'd like to know more too, but I'm wondering about something else also. Note the shaved area of the bullet in my picture above. Forward of that, as I've noted, measures .3065", the shaving has piled up to .324", and to the rear of it the band measures .313". I've read on this forum about many shooting bullets sized .309" .310" or .311". Given the squareness of the beginning of the throat, I'm wondering if all those folks are shaving lead there, and perhaps taking the chance that a gascheck will snag there and produce a pressure spike. No doubt not all rifles will be as sharp there as mine is, but it appears there's the potential for a problem that perhaps we should all take into consideration. No doubt there will be many replies of "I've shot thousands of bullets sized .309" or .310" without a problem", and I don't doubt that many have. But until some of the squareness of the throat erodes away via shooting jacketed bullets in my K31, it isn't going to see a gaschecked cast load unless I can find a .307" sizing die. Visualize if you can the pressure spike caused by a gascheck catching there and trying to turn its edge over so that it can head on down the barrel. I'll pass on taking the chance of having my rifle turn like slugs, cause I know my luck, that piece of receiver would be in the middle of my forehead!

[jack19512]

I have always had good luck with my K31's with sized .308 boolits. I'm no expert by any means but myself I would never try a .314 diameter boolit in a K31.

[JSH]

Your thoughts have some merit. I think a different bullet design would solve the problem.
That looks to be the lee designed for the 7.62x39?
I went and bought one of the 6 bangers a while back, folks said it would work in the K31's. Mine don't like it. BTW mine did shave when the would chamber.
Went back to the RCBS 165 sil bore rider. I waqs tempted to go the 6 banger route on that on too. Then decided quality was better than quantity.
I would sure like to have the same bullet that would drop at .310 and another at .313, with a proper sized nose for each.
This particular design has worked very well to excellent in evrything it will fir properly in.
jeff

[madsenshooter]

It's an old Belding and Mull 311169. With lino it casts them at .313". Someday I'm going to get around to trying some in my Krag sized to .310" to fit the throat and their oversized bores. I'd sure like to be in on the autopsy of ka-boom, wonder just where that bullet is? I've done a bit more measuring, the warning in the old Hornady handbook about overloads being particularly dangerous in the Swiss rifles because the case head is not fully supported, is also viable in the K31. With Graf's brass there's about .060" that's unsupported. I like seeing the whole case head disappear into my Krags and Arisakas.

[wildwilly]

I apologize for this question being a bit OT, but since a number of Schmidt-Rubin shooters are here, I wish to inquire: several decades ago (1960's) Martin B Retting was offering for sale S-R's rechambered to 308 Win. Are these rifles still being encountered in the field? How did they perform? Thanks.

[Shepherd2]

Every once in a while a Schmidt-Rubin rechambered to .308 Win. comes up for sale on GunBroker. Something to be avoided IMO.

[Bob S]

This one is 7.62x51 .. metric designation for .308 Win.

http://img.photobucket.com/albums/v76/BobS1/K31/CISMK314.jpg

FrankenSchmidt is one of those "Alpine Sporters" of the 60's: a 96/11 shortened, barrel set back and rechambered to .308. This one sits in a K11 stock for the time being.

http://img.photobucket.com/albums/v76/BobS1/Swiss/FrankenSchmidtPHsights.jpg

I have another of these in a Herter's stock; no pictures of that one.

I've been shooting the two S-R's (the K31 is not a S-R) for many years with no troubles. I don't attempt to hot rod them, and I don't shoot commercial ammo in them ... it costs too much and does not perform as well as my own handloads. GI Match does really well in them.

In any of the Swiss Straight pulls, extraction will get difficult before the pressure gets dangerous, so if you're working up loads as you should, that is a limiting factor. Neither the S-R nor the K31 will handle escaping gas very well, but the S-R will vent it to a better degree than the K31. Unfortunatly, most would go through the magazine.

Depending on what the intended charge was, a double charge of 2400 could cause that much damage with no other contributing factors. If the case neck has no room to expand and release the bullet in addition, then it has the makings of a bomb.

Resp'y,
Bob S.

[TAWILDCATT]

that was a lead bullet.I would think that the lead would melt if hot enuf.also just squirt.the lead would not stand that pressure.I shoot a 1903 [1914 made]with 311291 as cast.and its a tack driver.I use Red Dot.
no damage to barrel most to reciever.it was not the bullet.
remember the jap that was rechambered to 30/06 with a 6.5 bore.and fired fine.:coffeecom[smilie=1::coffee:

[Doug Bowser]

that was a lead bullet.I would think that the lead would melt if hot enuf.also just squirt.the lead would not stand that pressure.I shoot a 1903 [1914 made]with 311291 as cast.and its a tack driver.I use Red Dot.
no damage to barrel most to reciever.it was not the bullet.
remember the jap that was rechambered to 30/06 with a 6.5 bore.and fired fine.:coffeecom[smilie=1::coffee:

Guys, it is a simple concept. The size of the bullet going down the bore is not the problem. The bullet being that oversized causes the cartridge neck to be pinched by the neck area of the chamber. If there is no clearance and there is forcing of the loaded neck into the chamber, causes a harder bullet pull from the cartridge neck, causing pressures to skyrocket.

I had a friend with a nice 98/09 Argentine Mauser in 7.65x54mm. He formed cases from .30-06 brass. He experienced high pressure because he did not check the loaded neck diameter of his reloads. It to open the bolt he had to use a hammer handle and the primers fell out of the brass. Whenever shortening cases or reforming cases, check the loaded neck diameter.

Be careful out there the reloading demons are at work.

[madsenshooter]

I asked Wally Enga, he says he has fired thousands of .314 cast bullets through several K31s without incident, he didn't say how he got them to chamber, maybe he turns the necks of his cases. But from that it appears maybe we're looking at a double charge. The unsupported portion of the case wouldn't handle the pressure. Concerning the 6.5 Arisaka that shot 30/06, the case head of that round would have been surrounded by the steel of the chamber or I imagine the pressure needed to swage that .30 caliber bullet down to 6.5 would have ruptured the case like this one. Without more facts, we can but speculate. Although it raises pressures, a neck that doesn't expand a bit to release the bullet isn't going to stop the bullet from going. Benchresters that use custom cut necks in their chambers will tell you that, so can I as I have made 6.5 Jap cases from LC 308 brass and turned the necks so that there is no expansion upon firing, after firing you can't put a bullet back in the case by hand. Loads have to be adjusted accordingly.

[Bret4207]

I've rear and re-read all this. I'm of the opinion it was probably a overcharge. The K31 is adequate for high pressure loads, but an over charge of a fast powder would be beyond the brasses capability. I've routinely shot "oversized" cast boolits in a variety of guns. While this example is on the large side, I question if it would cause this. Now, a combination of the large boolit and an overcharge....kablooie! That unsupported section let go and the gas did the rest.

[Ricochet]

Given the squareness of the beginning of the throat, I'm wondering if all those folks are shaving lead there, and perhaps taking the chance that a gascheck will snag there and produce a pressure spike.
I believe my K-31's chamber end ledge shaves what's over .308", and that's what I size my boolits to.

[B747]

I asked Wally Enga, he says he has fired thousands of .314 cast bullets through several K31s without incident, he didn't say how he got them to chamber, maybe he turns the necks of his cases. But from that it appears maybe we're looking at a double charge.

Well not exactly what I said about this incident --- but I have fired 314299 C/B's
thru several of my K31's by tapering the front drive bands down until they will chamber with no indication of any noticable pressure increase in the quite low pressures we have with cast bullets for target shooting --- velocities of only 1200 to 1700 fps. My normal target cast bullet in the K-31 is either the RCBS-165 SIL or Lyman 311672 sized at 310.

I can't claim to have any real expertise in the failure mode of this K31, but I will give you my personal opinion on this incident.

I don't think the factor that the cast bullet was sized to .314 had any bearing in this case

Two possible scenarios for this failure mode --- the first and most likely, a double charge of his 2400 load, which would result in a real dangerous pressure range.

The other possibility is that the bolt cam follower plate lug tip broke off and allowed the rifle to fire with the bolt locking lugs out of battery.

Wally

[Sanchez]

Am also leaning towards the double-charge scenario here, & very glad to not hear of any serious injury from this record book-class catastrophic failure.

Do hope that by now ya have impounded & pulled-down any remaing live rounds from that same loading session ..... :groner:

[Leadmine]

Thanks fo rposting this since its a real life situation that can and does happen.

I agree about the bullet size, seems too large. But I also think that the observation about the out of battery situation is contributory. I had a couple of these rifles and tho they are accurate shooters, I'm not a big fan of straight pull. I also think there are inherent problems with venting in the design. Nonetheless I'm not chatting to annoy people who are fans of these rifles.

When I was first working up loads for these rifles, I noticed quickly that with the short throats, bullets need to be seated rather deep. I remember a couple times at the range when the bolt wasn't into battery...its very hard to tell, and I pulled the trigger and heard a click. On one occasion, rather than retracting the bolt, I hit it with the palm of my hand to seat it and the gun went off. I did this twice, before I learned it is uncool to try and put the bolt into battery once the trigger has been pulled. Its very easy to think the bolt is in battery on these rifles when it is not.

Hard to tell all that happened here, but the bolt outta of battery situation is something that K31 shooters need to be aware of. I sold mine. Don't miss 'em one bit.

[Ricochet]

Very true about problems getting the bolt fully closed and locked. The firing pin's supposed to be blocked in that situation so it can't hit the primer, and the blow of the falling striker drives the bolt into battery. Usually it'll then fire on recocking and trying again. But tight fitting cast boolits make it a lot harder to fully close the thing. The oversize bore riders on my Lee C309-200-R boolits often require a hard blow or two on the handle to finish the job, leaving my hand bruised. A tight boolit like that could stop the thing right on the margin of where it can fire, without being fully locked. And there's bound to be some variation among different rifles as to how much out of battery they can possibly be fired.

Personally, for now I've pretty much relegated my K-31 to jacketed bullets and shoot the cast in the much more tolerant chambers of my 1911 and 1896/11.

[bandit7.5]

I have a question if the reciever is blown up does that make it a demil and legal to ship without a ffl.

[Leadmine]

Yea, demilled in a fraction of a second. I would say yes, although it looks like there isn't much left to salvage other than the butt plate and the sights.

This rifle is best left just as it is, displayed where people can see it so they can understand the potential that exists when things go bad. 60,000 PSI whizzing around uncontrolled is a dangerous thing and seeing this is worth more than can be salvaged from the rifle at this point.

[diopter]

Here's a slide show of the pictures and video I took.

http://news.webshots.com/slideshow/568637838dtAdYb;jsessionid=abckycm6PHBh99p5GLu2r

[madsenshooter]

Nicely done! According to some photos of sectioned cases I've seen on another board, done by parashooter, Norma cases have the thinnest heads. Just this guy's luck to happen to be using them. What of the boolit? Long gone? Any other helpful info offered by the unfortunate one? What I mean is, did he have the round chambered or was he hitting the bolt when it went off, things like that.

[Geraldo]

I'm betting on one of two possibilities:
1. Double charge of 2400.
2. Right charge weight, wrong powder. I saw the remains of two Remington M700s where the reloader had set his measure correctly, but instead of Reloader 7 he used AA7.

[Ricochet]

...the reloader had set his measure correctly, but instead of Reloader 7 he used AA7.
I've seen that confusion pop up in discussions on this board.

I have to be especially careful of the surplus WC860 and WC680 I have in identical white plastic jugs. I've mistyped one powder number for the other before.

[Bear Claw]

If the charges were reasonable w/2400 I don"t believe that would blow the gun up, unless it was "hot-roded" a little to much then I could see it as well,
The boolit diameter is I think a contributing factor, The ogive on a factory round is somewhat different than what is used in the U.S. and I have talked w/ several re-loaders who couldn't seem their wrap their minds around this,
Then after they load some rounds they find they cant chamber the ammo
"IE: the bolt will not or is hard to close"....

I have a vision of this .314 boolit being pushed back into the case, or the shooter "whakin" the bolt handle till it closes, I know these guns shouldn't fire OOB but I have seen it happen myself....."" OOB = out of battery"....

I use a lot of 2400, in my K-31 I use 21gr
in my 03 spfd I use 20gr these are LIGHT loads w/cb"sw/gc

Neither load shows any sign of over psr, Also as was posted b-4 a mix-up on the powder could do it quit handily.

Anyway thats my.02:bigsmyl2:

[mto7464]

Ricochet, you should try the Lyman 165 sillywet in your K31. Mine mold cast them at .310 and I size them to .308. Boolit seating with Lino or WW is at about the crimp groove of the Boolit (if that what that groove is). They shoot great too.

[Ricochet]

Yeah, I've heard that. Probably should've gotten in on the group buy for the 6-hole modified one, but at the time I was overextended. I still think the nose of that one's too fat at .300", but it's way better than the oversized bore riders I've got. All of my .30 caliber moulds are fat thirties, by design or by accident.

[EDG]

When you use a faster burning powder than designed for the round you have to KNOW each round was loaded correctly.
Learn to look at the charge level with a flash light before seating the bullets.

[superior]

I think if the case gets piched and can't expand, the subsequent explosion will also cause the case to fail. Just my forensic analysis.

[yodar]

I'd like to know more too, but I'm wondering about something else also. Note the shaved area of the bullet in my picture above. Forward of that, as I've noted, measures .3065", the shaving has piled up to .324", and to the rear of it the band measures .313". I've read on this forum about many shooting bullets sized .309" .310" or .311". Given the squareness of the beginning of the throat, I'm wondering if all those folks are shaving lead there, and perhaps taking the chance that a gascheck will snag there and produce a pressure spike. No doubt not all rifles will be as sharp there as mine is, but it appears there's the potential for a problem that perhaps we should all take into consideration. No doubt there will be many replies of "I've shot thousands of bullets sized .309" or .310" without a problem", and I don't doubt that many have. But until some of the squareness of the throat erodes away via shooting jacketed bullets in my K31, it isn't going to see a gaschecked cast load unless I can find a .307" sizing die. Visualize if you can the pressure spike caused by a gascheck catching there and trying to turn its edge over so that it can head on down the barrel. I'll pass on taking the chance of having my rifle turn like slugs, cause I know my luck, that piece of receiver would be in the middle of my forehead!

a friend on another list had laid down a handy rule of thumb that works for me
whether I use a cast or ja**ed bullet in K-31

The bullet MUST be strongly tapered.

The seated bullet MUST read .301" 0.170" ahead ( close to an N drill size) ahead of the case mouth to demonstrate the taper the short-shaved throat the K-31 demands

yodar

[WineMan]

I use a wooden dowel with a piece of tape at the edge of the neck to check charges. Mark the dowel from a weighed charge and then it is set for the bunch.

Wineman