K31 Accurizing

This forum is dedicated to the discussion of the Swiss Schmidt-Rubin Series, the K31 series, and the 1893 Cavalry Carbine.
Doctor Xring
Joined: 26 Jul 2006, 09:34

12 Sep 2006, 18:46 #1

One of my plans is to use a K31 for Highpower matches. I have been
shooting the rifles in stock condition and have found them to be
accurate to a point. They have many qualities that allow for intrinsic
accuracy. Excellent barrels. Stiff actions. Very good cartridge design. Excellent triggers. Very good bedding for a service rifle. But it is this
last point that I have been working on. Since I do not have to live
with the compromises demanded for a bayonet, I believe I can set
up these rifles for a more stable and therefore accurate condition.
The two rifles in this test have been giving good groups with GP11
but often will have flyers, some point of impact changes, and will
begin to walk impact on long strings. Since two of the stages of
Highpower rifle demands 10 shots rapid fire, this is not acceptable.
I did three things to the rifles. I drilled out the action attachment
points and epoxied an insert in each one. These are flush mounted
to the bedding surfaces. This step was taken to take the variable
of action torqueing when tightening the guard screws out of the
equation. You do not compress the wood. You tighten onto these
metal inserts, thereby "floating the action", so to speak. This is
a technique similar to pillar bedding. I used a drill press to
drill out the front and a hand drill to drill out the back. Using
incrementally larger bits with the hand drill made it very easy
as the bit just followed the original hole. The inserts are 3/8"
in diameter.
The next thing I did was to bed the chamber area in front of the
action with acraglas. If did this for further stabilization in this
axis. I did not bed the recoil lug on the trigger housing because
I really don't think it is needed. The original bedding looked
superb on both rifles.
The last thing to be done was to remove any contact with the
barrel at the upper band area of the stock and handguard.
Both rifles, when the handguard was off, were free floated
as far as the stock was concerned. But the handguard would
put downward pressure on the barrel when the bands were
tightened down. I relieved this contact with sandpaper around
a correct fitting dowel rod to maintain the circular cut on the
handguard. I relieved just enough to slide a piece of cardstock
between the barrel and stocking. You can see in the one pic
how the handguard contact point is glazed from the barrel
rubbing on the handguard. All K31's I have disassembled
have this condition.
I took the rifles out for a test today using GP11 ammunition.
The rifles were set up with a St. Marie's scope mount with
12x scope. Five shot groups were circular in shape and around
1.25 to 1.5 MOA.
Now for the test. Rapid fire 10 rounds, starting from a cool barrel.
I fired the rounds as fast as I could return to battery and get a
good hold. Looks good so far. Next will be handload testing.
Enclosed are pics of the bedding process and the rapid fire targets
for each rifle.
The whole process took about 2 hours total for each rifle
at a cost of about $8 each.
good shooting, Chris



12 Sep 2006, 19:29 #2

Do any of these mods, especially the relief at the hand guard, make the rifle feelfor lack of a better termloosy goosy?
Outstanding post with wonderful pics by the way. I've just archived it.

Doctor Xring
Joined: 26 Jul 2006, 09:34

12 Sep 2006, 21:06 #3

The goose is not loose.
I relieved the wood rather than use spacers
on the bands for that very reason.

Joined: 13 Dec 2002, 01:46

12 Sep 2006, 23:33 #4

Cool experiment! I have a mismatch K31 I put together from different bits and pieces I think I'm going to try to emulate your procedure there. I have P's threaded damper on it already and it performs adequate but not as good as my unaltered champions... I wonder if doing something like this would tighten it up???
"E Svizzeri sono armatissimi e liberissimi"
"The Swiss are the most armed and the most free"
N. Machiavelli, Il Principe Capitolo
"E Svizzeri sono armatissimi e liberissimi"

"The Swiss are the most armed and the most free"

N. Machiavelli, Il Principe Capitolo XII

Doctor Xring
Joined: 26 Jul 2006, 09:34

13 Sep 2006, 04:52 #5

I meant to include a thanks to Guisan on the
orginal post on this project.
He helped me by sending me some great
diagrams and information about the bedding
system on the K31 and also the ZfK55 rifles.
Thanks dude. You 'da man !

Joined: 15 Feb 2003, 19:48

13 Sep 2006, 09:50 #6

Yes, Guisan is quite a treasure trove of useful info and items.
He Rocks!Alan in Michigan

">Curio and Relics Firearms Forum Swiss Rifles

Zeughaus Hawkster

Alan in Wisconsin

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Joined: 13 Nov 2002, 02:21

13 Sep 2006, 16:49 #7

This is an interesting approach. I am not sure why you needed to glass bed the chamber part of the action, ahead of the big action lug. It is my understanding that the big front lug is the pivot point, and the barrel is moved up and down by adjusting the tang screw. I believe there should be no contact with the stock by the front/chamber part of the action, as this would need room, however slight, to move up and down. Was your intention to stabilize the action and barrel in a sideways direction? Does this bedded area now hold the front part of the acton firmly? Does this not then move the pivot point forward to this area?
Forgive my awkwardness with some modern terminology. I'm firmly rooted in the 18th Century, and the accurizing concept for the K31 works fine for me if I think of it as adjusting the elevating screw on a six-pounder field gun!

Doctor Xring
Joined: 26 Jul 2006, 09:34

14 Sep 2006, 02:21 #8

Hi Bruce -
Yes, that is right. I bedded chamber area of the rifle
to stabilize the rifle on a left/right axis but also
to reduce load on the action. I believe you are
right though. It may not be necessary. But I have used
this before when bedding other rifles to give some support
to the action by reducing the load mass of the barrel on
the action. It may be just fine both ways.
In the ideal K31 rifle I believe you would have the front guard
screw tight, holding the front lug firmly against the shim plate in
the recess. You would have the back screw tight firmly
holding the tang against the top of the stock. The recoil
lug (back of the trigger housing) would be dead against
the stock. The barrel would be held securely between
the forestock and the handguard. All would be at rest
with no torque. The "miracle" walnut stock would never
compress or change position or load at any contact point.
The harmonics induced on this rifle by the perfectly matched
GP11 round would hum and the bullet would go through the
same hole every time.
But things don't work out that way. So we compensate
as best we can and come up with things to take out
variables and make things repeatable.
I don't believe the idea was to use the front lug as a pivot
point, tuning the rifle by screwing the rear guard screw in
and out. But some rifles will respond to this treatment
to try and balance out deficiencies in the action bedding
and varying barrel conditions in contact with the stock.
Mauser rifles also respond to this treatment in the very
same way for the same reasons. This can be done
but how stable is it ? How repeatable is it after taking
the rifle down for maintenance ?
We now have some things that have come along to work
things like this out. Composite stocks for one. But that
won't apply here. Pillar bedding is another. That's what
I am working with here. To create a more stable platform
for the action to ride in the stock. To set up this rifle where
it will be stable and be easy to maintain. The rifle set up
with the inserts will not pivot, or that is the idea. Every
time you cinch up the action screws the action will be
in the same position, under the same load. The barrel
will rest in the epoxy bed the same each time. (By the
way, when I put the action in the stock with the acraglas
gel in it, I applied the same tension to the screws as I would
if the rifle was being put together for use.) And again, I
am not having to worry about having a strong situation to
mount a bayonet on, so I can free float the barrel. This
in itself is a major help.
This project is still green. It's too early to say all is well
yet, but I think something close to what we have here
will work.
Bedding, barrel, and bullet. These are the keys to accuracy.
The Swiss with their K31 rifle and GP11 ammunition did a
marvelous job with all three. After I became familiar with
the K31 I was just totally taken with it. It has become my
favorite military rifle. It appeals to me in a lot of ways.
The whole K31 system just exudes with the long and deep shooting
culture of Switzerland. The Swiss may never have gotten into a
scuffle with these rifles, but they were ready for head shots
if they did ! K in K31 stands for Karabiner. But for me it
also stands for King. The King Kong of military bolt guns.

Joined: 09 Mar 2006, 01:36

14 Sep 2006, 08:36 #9

Interesting Chris ! So far, I used spacers on my 2 rifles and both shoot < MOA. However, my 1st. shot out of a cold bbl. is always out so that my 1st. group is never the best. Once warmed up, all is fine until I let it cool and then the scenario repeats itself. I was thinking of free floating the bbl. completely (NB.: the spacer lifts the handguard off the bbl. but there's still pressure from the forend beneath) and your experience has convinced me. I did it on my beech stocked rifle (saving the nicer walnut one for later) and found that sanding out the end "step" at both forend and handguard gave the right clearance all around the bbl., without affecting looks and stock rigidity. I'll go to the range next Saturday and try it out. Andr

Doctor Xring
Joined: 26 Jul 2006, 09:34

18 Sep 2006, 23:04 #10

I did some range testing with handloads on the
two K31's that I did the pillar type bedding on
All combinations shot well. 3 combinations shot
in 1 MOA for 5 shots and 1 shot 10 shots
in 1 MOA. All bullets seated just off of the
lands. Federal 210 primers.

The 5 shot 1 minute loads were --
Nosler 155 gr J4's
45 gr. IMR4064
46 gr. DP74
Nosler 168 gr J4's
45 gr. DP74

The best shooting load of the day
was this one below with 10 rounds
in 1 MOA.
Nosler 168 gr. J4's
47 gr. H4350