Reloading for Swiss K-31

[concretus]

Hello,
I purchased a K-31 about a month ago. After doing some research before I made the purchase, these are superbly built rifles capable of moa accuracy. Reloading date is limited though. I have somewhat of a load worked up for it using the Sierra 168 hpbt and IMR 4064. I was wondering if there was anybody that has any experience loading for this rifle and what kind of recipies the developed. I would think since the 7.5X 55mm Swiss is very close to the .308 win/ 7.62X51mm, that the powders that are used for the .308w could be used for the 7.5 Any information would be greatly appreciated.

Information

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[Parashooter]

Don't believe everything you see on the internet. The Swiss make fine rifles, but the K31 doesn't normally give "moa" groups. With good ammunition, it's reasonable to expect 5-shot groups at 100 yards to average 1.5 to 2.5 inches. Occasionally we see a tiny group, and folks love to brag about them, but that's not what to expect as normal performance in the long run.

The 7.5x55 case has about 13% more powder volume than .308 Winchester, meaning that the Swiss cartridge can benefit from higher-volume loads of slow powders that simply would not fit in the .308 case - and that .308 data used to load 7.5x55 will normally yield lower pressures and velocities, all else being equal. The higher the loading-density, the greater the discrepancy will be. Image below shows pressure and velocity estimates for identical charges in the two cartridges.



It's not generally advisable to solicit specific load information on internet forums. There's just too much that can go wrong - from simple typing errors to malicious information. If you look at powder manufacturer's websites and published manuals, you can find plenty of reliable data for a variety of powders. Here's a sample from Sierra's manual.



Because this Sierra data was developed in the 1911 rifle, the OAL figures are too long for the shorter-throated K31, which requires deeper seating.

[gulliver62]

This is a good source for K-31 reloading info. I am headed down the same path you are.
SwissRifles

Many of the discussions I have seen are around trim-to length and OAL. The K-31 "does not tolerate long rounds"

Specifically: Swiss Handguns 1882

I know the link says Swiss Handguns but scroll down when you get there

[concretus]

That is excellent information!!! Than you very much!!! Especially the bullet seating chart. You are right, My O.A.L. w/ Sierra 168 match is 2.895" I wanted to also try AA2520. The tech at Sierra said it would be safe to start at the .308win minimum load and work up. So you are saying that a slower burning powder like say IMR4350 might be more beneficial due higher case capacity and larger charge?

[Patrick Chadwick]

Thank you Parashooter for an excellent diagram!

It illustrates how, if you want to get the best performance out of any rifle, it is not sufficient to follow specification sheets, whether CIP or SAAMI. The bullet seating depth needs to be tuned to the specific rifle. The difference between the K31 and the G11 is similar (in principle, if not actual figures) to the difference between any new rifle, and what a well-used, 100-year old example might be.

Patrick

[Patrick Chadwick]

The pressure/velocity/distance diagram also illustrates quite neatly that, with a 25" barrel, the Swiss cartridge is going to produce approximately the same muzzle velocity as the 308 cartridge with 20" barrel.

The work done on the bullet is the integral of (force x distance), i.e. proportional to the area under the pressure curve. The area under the pressure curve section from 20" to 25" for the Swiss cartridge is roughly the same as the difference between the 308 and the Swiss curves at the start of the curves. But the peak pressure is considerably lower, for the same amount of energy imparted to the bullet.

Which is the simple reason why those old, long rifles can achieve a trajectory that is nearly as flat as more modern "carbine" length rifles, but with a slower powder, lower peak pressure, and a generally more "shoulder-friendly" behavior. Something which I favor more and more with every year! (My Swiss is one of the last G96/11s)

Patrick