Old timey rifles and "cold bore" shots; thoughts on rifle harmonics

[kitchengunsmith]

So I was shooting my K31 in the snow the other day, the way God intended, doing some load development, and I encountered something I have never actually seen before: actual significant "cold bore" point of impact changes. I was shooting 3 shot groups(cuz I can't afford 10 shot groups) and with every single group I shot the first shot was way high and the other two would hit about 4 inches lower, within an inch of each other. I wasn't cleaning the rifle between groups or doing anything differently from one group to the next except leaving the rifle in the freezing cold while I swapped out targets. I was increasing my powder charge in increments of .5grains with each 3 shot group; the point of impact would shift accordingly, but each group looked the same with one way high shot and two shots right next to each other.

For those that don't know, the K31 has a little metal chingaderro on the bottom of the fore end of the stock that pushes upward on the barrel. This was done to a lot of old military rifles as a way of harmonically tuning the barrel. The only reason I can figure for my rifle acting this way is that the combination of rapidly changing barrel temps interacting with a wood stock and said chingaderro putting pressure on the barrel caused my rifle to have a completely different harmonic signature cold than it did once the barrel warmed up a little.

I am really curious to hear people's thoughts on what was going on with my gun. I would especially like to hear from anyone who has experimented with full length glass bedding of the barrel.

 

[Laphroaig]

The design of the K31 has the barrel essentially free floating. Check out the following for a discussion of that:

https://www.tapatalk.com/groups/the...geboard/free-floating-a-k31-barrel-t5871.html

I'd pull the stock and see if there are any dark, shiny places that indicate the barrel is rubbing there. That would be your problem area, most likely.

 

[Lafitte]

I am not trying to over simplify things, just my own thoughts and practices. For hunting rifles cold bore accuracy is the standard, I have never shot a deer or any game with a group. For rifle shooting for score it's another ball game.
Lafitte

 

[Ks5shooter]

^YUP^^^^^this

 

[Dr T]

How cold was it?

 

[stillquietvoice]

May not be in contact with barrel on cold bore shot. May not contact till barrel warms up some.

 

[chicharrones]

The design of the K31 has the barrel essentially free floating. Check out the following for a discussion of that:

https://www.tapatalk.com/groups/the...geboard/free-floating-a-k31-barrel-t5871.html

I'd pull the stock and see if there are any dark, shiny places that indicate the barrel is rubbing there. That would be your problem area, most likely.

Good info there, thanks.

 

[someguy2800]

My handi rifle does something similar. First shot is always 1-1/2” high and the next 4 will print a nice round group. It’s the same every time. It’s the only rifle I have that shows any noticeable change as the barrel warms up. When I prepare that one for deer hunting I don’t even bother shooting groups, I just shoot a cold bore shot and note the POI, then repeat the next day.

 

[PapaG]

I had a 10-22 target that would throw the first round out of a magazine from 1/4 to 3/8" out. To save points I had to load one extra and shoot the first into the berm.
I've been working on an article about first shot accuracy for years. I have a target for each of several rifles, and one slug gun, that gets a cold bore round fired at it each time I go out. Kind of funny how the "groups" aren't too bad, just not where subsequent shots go. For hunting, I sight in to the cold bore zero.
Still work to do.

 

[kitchengunsmith]

What's the little chingus in the fore end of the stock if not for putting pressure on the barrel?

 

[boom boom]

Upper barrel band for mounting bayonet and stacking device if you are referring to this


Might find this useful as it is a picture by picture guide to disassembly and parts naming
http://thisoldrifle.com/swissk31/rifledisassembly/index.asp

Otherwise you are talking about the metal edges on the handguards that are designed to prevent chipping and cracking. Now, the Schmidt Rubin series which ended with the 1911 and k11 rifles had a tension collar of aluminum (like the m28 Finnish Mosin) around the barrel where it went through the upper barrel band for accuracy and replicability reasons.

The K31 is intended to have a free floating barrel with only two points of contact of the receiver to the stock via the receiver screws. However, who knows what the prior owners of your rifle did with it.

 

[kitchengunsmith]

Upper barrel band for mounting bayonet and stacking device if you are referring to this
View attachment 827019

I'm talking about the little metal bit in the bottom of the barrel channel, I'll post a pic later in the day

 

[boom boom]

That is not so much for accuracy but instead to protect the front of the stock from splintering, compressing, and cracking. As the k31 barrel is free floated, the metal reinforcement on the stock tip and handguard end allows the upper barrel band pictured above to be tightened enough for stacking and bayonet mounting purposes without affecting the free float of the barrel, otherwise if not reinforced, the wood of the stock and handguard can deform into the barrel channel affecting accuracy if the barrel band is tightened too much or used in bayonet practice. It would also cause cracking and compression of the wood when using a bayonet such as a common problem with U.S. 1903 stocks that have no metal reinforcement on the stock tip.

 

[kitchengunsmith]

I'm talking about this thing

 

[kitchengunsmith]

It actually doesn't contact the barrel now, but there is a little scuff mark on the barrel right where it would sit like it was mated up against it at one point.

 

[boom boom]

It actually doesn't contact the barrel now, but there is a little scuff mark on the barrel right where it would sit like it was mated up against it at one point.

That looks to be a barrel tensioning device designed to put adjustable upward pressure on the barrel. The last time that I dismounted a K31, I do not remember seeing one in my barrel channel and know that the K11/1911 does not have this. I suspect that this was a little goodie added by whoever kept/owned the rifle (Swiss militia take and store their weapons at home (or did so in the past with K31's)). Some were also sold new to civilians which begin with a special serial number that I do not recall offhand. The Swiss have a tradition of shooting competitions so it is possible that someone altered this to improve their rifle's performance. Pretty sure it is not issue.

 

[kitchengunsmith]

That looks to be a barrel tensioning device designed to put adjustable upward pressure on the barrel. The last time that I dismounted a K31, I do not remember seeing one in my barrel channel and know that the K11/1911 does not have this. I suspect that this was a little goodie added by whoever kept/owned the rifle (Swiss militia take and store their weapons at home (or did so in the past with K31's)). Some were also sold new to civilians which begin with a special serial number that I do not recall offhand. The Swiss have a tradition of shooting competitions so it is possible that someone altered this to improve their rifle's performance. Pretty sure it is not issue.

OK that makes sense. I kinda figured it was a standard issue thing. I always kinda figured the barrel tensioning thing was supposed to make up for the barrel being snug against the wood by the front barrel band cuz its pretty snug on my gun. now that I know its not currently contacting the barrel, I'm thinking the wood just swole up over time and grabbed the barrel up front and pushed it off the chingus in the barrel channel. Thank you for helping me figure that out

 

[kitchengunsmith]

I had a 10-22 target that would throw the first round out of a magazine from 1/4 to 3/8" out. To save points I had to load one extra and shoot the first into the berm.
I've been working on an article about first shot accuracy for years. I have a target for each of several rifles, and one slug gun, that gets a cold bore round fired at it each time I go out. Kind of funny how the "groups" aren't too bad, just not where subsequent shots go. For hunting, I sight in to the cold bore zero.
Still work to do.

Are you cleaning your guns before your cold bore shots? I've found that a squeaky clean bore can exacerbate the point of impact shift of a cold bore shot.

 

[PapaG]

Other than black powder guns, I don't clean until accuracy falls off.

 

[Frostbite]

I often shoot in the very cold temperatures during winter and do not see noticeable difference between cold bore shots in winter versus summer, but yes, some rifles are shifting point of impact as they heat up. The worst for that was a Remington 760 Gamemaster in 30-06 I once owned for a few years. It was shifting to the right as it got warmer. That one was also a shoulder bruiser in the summer with its metal butt plate, I don't miss it at all.

 

[PapaG]

I have one that walks up, another that walks down. Another, a 10-22 with Shaw barrel and Bentz chamber doesn't seem to care and an old Anschutz sporter needs from five to fifteen shots to settle down. When it does, it is good for the day.

 

[Tommygunn]

So I was shooting my K31 in the snow the other day, the way God intended, doing some load development, and I encountered something I have never actually seen before: actual significant "cold bore" point of impact changes. I was shooting 3 shot groups(cuz I can't afford 10 shot groups) and with every single group I shot the first shot was way high and the other two would hit about 4 inches lower, within an inch of each other. I wasn't cleaning the rifle between groups or doing anything differently from one group to the next except leaving the rifle in the freezing cold while I swapped out targets. I was increasing my powder charge in increments of .5grains with each 3 shot group; the point of impact would shift accordingly, but each group looked the same with one way high shot and two shots right next to each other.

For those that don't know, the K31 has a little metal chingaderro on the bottom of the fore end of the stock that pushes upward on the barrel. This was done to a lot of old military rifles as a way of harmonically tuning the barrel. The only reason I can figure for my rifle acting this way is that the combination of rapidly changing barrel temps interacting with a wood stock and said chingaderro putting pressure on the barrel caused my rifle to have a completely different harmonic signature cold than it did once the barrel warmed up a little.

I am really curious to hear people's thoughts on what was going on with my gun. I would especially like to hear from anyone who has experimented with full length glass bedding of the barrel.

I have to wonder; is "chingaderro" a real teschnical term?

 

[kitchengunsmith]

I have to wonder; is "chingaderro" a real teschnical term?

It's Mexican for 'chingus'

 

[Steve S.]

A “chingus” or “chingustito” is the inhabitant of a stream-bottomed wooded draw in a mountainous valley area called a “chingaderro”.