K31 sporadic misfires

[Duster340]

Hey Folks,

Been working on a new to me K31 project this year and experienced misfires when I took it out to sight in for deer season. My first experience with K31, so the action is not one I'm real familiar with.

The misfire scenario is weird with no consistent pattern to it. Load the magazine, work the action, chambers round fine, squeeze the trigger and it will fire. But other times just a click. When that happens there is no dent or firing pin contact mark on the primer. I eject the round and cycle the next, sometimes it goes bang, other times I get no hit on the primer.

I'd think if a weak spring were the culprit I'd at least see a light primer strike or contact mark on the primers.

Since my last outing, I've read that the action needs to really be cycled firmly on the K31. Is this the case? And if so, just how hard does one need to pull back and close the action?

Thanks in advance for any assistance, input and suggestions. Hopefully I can get it sorted out in time for the bonus antlerless season Christmas week.

Be well all.

 

[Slamfire]

Hey Folks,

Been working on a new to me K31 project this year and experienced misfires when I took it out to sight in for deer season. My first experience with K31, so the action is not one I'm real familiar with.

The misfire scenario is weird with no consistent pattern to it. Load the magazine, work the action, chambers round fine, squeeze the trigger and it will fire. But other times just a click. When that happens there is no dent or firing pin contact mark on the primer. I eject the round and cycle the next, sometimes it goes bang, other times I get no hit on the primer.

I'd think if a weak spring were the culprit I'd at least see a light primer strike or contact mark on the primers.

Since my last outing, I've read that the action needs to really be cycled firmly on the K31. Is this the case? And if so, just how hard does one need to pull back and close the action?

Thanks in advance for any assistance, input and suggestions. Hopefully I can get it sorted out in time for the bonus antlerless season Christmas week.

Be well all.

Are you shooting reloads and if you are, how are you determining base to shoulder distance after sizing? If you are sizing the case too much, that is pushing the shoulder back too much, then you will experience failures to ignite.





Any suggestion to yank back hard and slam the bolt shut will in time damage the action bar. I really cannot fully express what I think of the idiocy of the advice you read.



Maybe the "docent" had not fully sized his brass below the chamber and found he had to beat on the bolt handle to get the lugs to go into battery. I have not tried to abuse my K31's, K31's were a service rifle, but service men were issued high quality ammunition that headspaced corrected . The stuff is almost match grade. It may be match grade but with irons and a service rifle, I am not going to see it.



I do want to say, I never have heard a Hatcherite address Swiss greased bullets beyond claiming that the Swiss used the ammunition to shoot holes in cheese. (That is what Captain Edward Crossman wrote) The Swiss were issuing ammunition with greased bullets from the 1880's up to the 1980's.



and they are still selling ammunition with greased bullets




This is what Hatcher said,

Hatcher's Notebook,1947

Cartridges should never be greased or oiled, and the bullets should never be greased. Grease on the cartridge or in the chamber creates excessive and hazardous pressure. It operates to reduce the size of the chamber and thus increases the density of loading and the pressure.

it is the current Army Ordnance Department position on greased and lubricated bullets, and yet, the Swiss are greasing their bullets.

Another question, how are you seating your primers? Do you verify that your primers are firmly seated?

And, what cases are you using?

 

[Duster340]

Thanks for the information Slamfire. Much appreciated. I was using this Hornady factory ammo from Grafs.

https://www.grafs.com/retail/catalog/product/history/1/orderId/1472929/productId/6889

Didn't even try my hand loads. New PPU brass 165 gr SPBT over loads of IMR 4895 and 3031.

The Hornady stuff cycled, chambered and ejected nicely with minimal effort. Which is why I too questioned the whole "Yank it open and slam it closed" stuff.

It's just really odd the the firing pin doesn't seem to hit the primers on some occasions. When it does fire, the strikes are quite positive and solid.

Take care

 

[amd6547]

If the bolt isn’t fully rotated into battery, you will get misfires.
That said, I ever throw my k31 bolt any harder than any other milsurp bolt action.

 

[Duster340]

If the bolt isn’t fully rotated into battery, you will get misfires.
That said, I ever throw my k31 bolt any harder than any other milsurp bolt action.

Hey amd6547,

Thanks for the response. I'll have to take it back out and be more cognizant of the cycling process. Being a new (to me) action, I wonder if I may not have been pulling the bolt to full battery. Definitely worth a look.

Thanks again man

 

[Slamfire]

Hey amd6547,

Thanks for the response. I'll have to take it back out and be more cognizant of the cycling process. Being a new (to me) action, I wonder if I may not have been pulling the bolt to full battery. Definitely worth a look.

Thanks again man

I got out my K31 and if you opened the bolt you cocked the mechanism. This is a cock on opening action. I do hope the firing pin is not following the bolt down into battery. I have a M1911 that did that, I think the Swiss owner stoned the sears for too fine of a final pull. I have to puzzle on that for a while and I think I fixed it.



you do better



Do you have a means, such as a Hornady comparator



to measure the base to shoulder distance on a fired case? If the base to shoulder distance on a fired case is 0.006" or more than that of an unfired case, then the Hornady factory ammunition is too short for your chamber. This is my first guess that the push feed extractor on the K31 is not snapping over the rim and the case is too far forward for the firing pin.

Also, as a firing pin check. Take the firing pin mechanism out of the bolt and clean the firing pin channel and inspect the firing pin mechanism. See if the firing pin has broken off the shaft.

If this is good, put it back together and determine firing pin protrusion. Take the bolt out of the rifle and figure out how to turn the lugs into battery, so the firing pin is forward. The tip will stick out of the bolt face. Measure the distance above the bolt face.

 

[amd6547]

To be clear, I'm talking about fully closing the bolt.

 

[JohnKSa]

Is it possible that the firing pin is broken? Sometimes the pieces line up right and you get a solid hit--sometimes they don't and there's no hit.

 

[Duster340]

I got out my K31 and if you opened the bolt you cocked the mechanism. This is a cock on opening action. I do hope the firing pin is not following the bolt down into battery. I have a M1911 that did that, I think the Swiss owner stoned the sears for too fine of a final pull. I have to puzzle on that for a while and I think I fixed it.

View attachment 876763

you do better

View attachment 876764

Do you have a means, such as a Hornady comparator

View attachment 876762

to measure the base to shoulder distance on a fired case? If the base to shoulder distance on a fired case is 0.006" or more than that of an unfired case, then the Hornady factory ammunition is too short for your chamber. This is my first guess that the push feed extractor on the K31 is not snapping over the rim and the case is too far forward for the firing pin.

Also, as a firing pin check. Take the firing pin mechanism out of the bolt and clean the firing pin channel and inspect the firing pin mechanism. See if the firing pin has broken off the shaft.

If this is good, put it back together and determine firing pin protrusion. Take the bolt out of the rifle and figure out how to turn the lugs into battery, so the firing pin is forward. The tip will stick out of the bolt face. Measure the distance above the bolt face.

Thanks for all the trouble shooting tips Slamfire. Gives me something to look at. I'll see if I can't get some measurements on the cases. What is the pin acceptable protrusion spec from the bolt face?

Take care

 

[Duster340]

To be clear, I'm talking about fully closing the bolt.

Roger that. Thanks again.

 

[Slamfire]

Thanks for all the trouble shooting tips Slamfire. Gives me something to look at. I'll see if I can't get some measurements on the cases. What is the pin acceptable protrusion spec from the bolt face?

Take care

I don't know and I did not find a number on the web. But, known values for US rifles are on the web.

This is from a post by Bill Ricca on another forum.

• M1 & M14............ Min. .044...............Max. .060
• M16 ......................Min. .028...............Max. .036
• M60 ......................Min. .035...............Max. .043
• .30 BMG...............Min. .060...............Max. .068
• .50 BMG M2........ Min. .073 ..............Max. .080
• M203 G/L............ Min. .032 ..............Max. .047

I would suggest that the M1 & M14 values are good enough. If your protrusion is below 0.44 by a lot, you may have a problem.

This link is worth downloading:

http://www.swissrifles.com/sr/english_k11_k31_manual.pdf

 

[Duster340]

Thanks again man. I do appreciate it.

 

[edwardware]

This is what Hatcher said,

Hatcher's Notebook,1947

Cartridges should never be greased or oiled, and the bullets should never be greased. Grease on the cartridge or in the chamber creates excessive and hazardous pressure. It operates to reduce the size of the chamber and thus increases the density of loading and the pressure.

It's kind of disappointing to see something so obviously wrong, and trivially testable, in Hatcher's work.

 

[Duster340]

So I took a closer look at the Hornady cartridges and while I still have to get a micrometer on them, it appears that the shoulder may be set back a bit further than my handloads. The bullets also have a distinct band around them. Not sure if that has any bearing on my issue. My load is on the left in the top pic, and right on the bottom pic. I'm going to give my handloads a shot next time I get to the range to see how they perform. Fingers crossed.

Thanks all

 

[boom boom]

You might check this gunboards forum discussion post first as they seem to have a similar issue to yours. https://forums.gunboards.com/showthread.php?320379-K31-will-not-fire! and a broken firing pin here https://www.tapatalk.com/groups/the...board/k31-firing-pin-fail-to-fire-t10608.html

Not sure if you have detail disassembled the bolt yet but I would also thoroughly clean the firing pin channel and the bolt and check for roughness of any parts. Also check for broken parts internally in the bolt as this has happened. The Swiss used a yellowish grease that is persistent and any crud could slow or block the firing pin channel just enough to get spotty ignition. There is also firing pin protrusion and to measure that you really should get the firing pin protrusion gage from Brownells. Someone on Swissriflesdotcom has probably already asked the question about fp protrusion in the k31.

Be aware that there are different bolt heads for adjusting headspace on these https://www.tapatalk.com/groups/the...board/the-four-k31-bolt-body-sizes-t6465.html

Guisan, a poster now deceased, was the fount of a lot of what we know in English about the k31. Here is a discussion of headspace and the k31 https://www.tapatalk.com/groups/theswissriflesdotcommessageboard/k31-bolt-head-markings-t13260.html

FWIW, My swiss rifles k11 and 31 do not require the rough handling that my m95 Steyr Ruck Zuck does. The worst of mine is a m48 Yugo Mauser which the advice is to work the action like you hate it. This is probably because the m48 was basically obsolete when issued and the Yugos kept a lot of them as new in war reserve. Use tends to polish the bolt and receiver a bit.