Accurizing Your Swiss Rifle
Pierre St. Marie
|I am not at all concerned with the built in accurizing
technique of pre-loading the stock. It is now my belief that this
accurizing technique from the manufacturer leaves too many variables in
the mix. Any flexing of the stock (being in direct, tight contact with
the barrel) will change POI at range. If ALL users of the k31 & 1911
were to shoot their rifles with the identical technique, EVERY time, I
may not have an argument concerning the armory shim/pre-loading
methodology. But............none of us do shoot identically other than
those in the shooting clubs, and, I suspect, even those good folks
introduce physical variables of their own at times. So...............
I've invested quite a bit of time in arriving at a rather simple conclusion I had always known, from experience, to be true. "Do not interfere with the barrel". That simple. Of course, none of us want to remove that classic stock and fore grip from the Schmidt Rubins, so I did the next best thing. I relieved all reasonable stress contact from the barrel.
I did this by designing a "spacer" meant to go between the flanges of both barrel bands. This simple spacer relieved the barrel of any meaningful contact with the stock. If the spacers are used correctly, the fore stock will feel "loose" at the barrel band. Of course, one could rout out the raceway to relieve the barrel, but I am loathe to remove any wood from the stock. Allowing the barrel to vibrate uninhibited definitely tightened up my groups. I had, of course, used a load capable of moa for these tests. This also meant that I could not use the sling in any kind of a bracing action. That would negate my efforts. Now for the second discovery. I found that "balancing" the tang screw against the receiver screw also had an effect on accuracy.
To determine spacer width requirements, loosen the screw on the front band until the band retainer will compress and release freely. The space you see between the flanges approximates the thickness required for the spacer. With the spacer(s) installed, the front to the stock should have a bit of "play", so that you can see/feel it move when you wiggle it. The rear band should also NOT grip the stock tightly. It, too should have a bit of play. This will leave the barrel relatively uninhibited by the stock. Also remember not to use the sling to "brace" the rifle. That tension will put pressure against the barrel too. Use the sling just to "steady" the rifle without undue pressure.
After installing the spacers, I begin by loosening both screws. I
coat the rear screw with LocTite. I then tighten the receiver screw dead
tight. I turn the tang screw down tight and back it our 3/4 of a turn or
a little better. You'll need to have around 30 dependable loads ready
for this test. Definitely do it from a bench rest, and if you have open
sights, use a clearly defined target at no more than 75 yards.