New Swiss K31 and reusing GP11 cases

Hi Guys:
I've got a tidbit that some of you might find mildly interesting.
First, I've another Swiss K31 in the barn. I'll post some photos in a little bit.
I wanted to ask a question in relation to K31's.
I have both GP11 ammo and hand loaded ammo for my K31's.
When reloading I use a Hornady comparator tool to set seating depth. I use the comparator tool to locate and specify how deep the bullet can travel before it hits the lands. The tool goes on your caliper and uses a interchangeable collet that uses the ogive of the bullet to determine bullet depth. With the tool you can set as far or close to the lands as you like. The special case for 7.5x55 Swiss has the back of the case threaded so the tool can be screwed on. The mouth is loose so a bullet can be put in the case and the bullet will slide easily. You put a chosen bullet in the case attached to the tool. You insert the case in the chamber, push the bullet forward and lock the tool down. Now you can pull it out and check the depth of the throat.
Ok, here's the question;
I check the depth with a 150 FMJ bullet and the reading says the bullet can't be seated more than 3.260 in. or a bullet to throat interference will occur. So I seat the bullet to 3.250 .in, now it's .010 .in off the lands. If the bullet is seated any more than 3.260 in. the bolt won't close, as expected.
Then I measure a GP11 round. It measures, with the tool, 3.325 in. .065 in. longer. So the bolt should not close, right? Remember the tool measures from the bullet ogive, not the tip, so all measurements made from the same arbitrary spot.
Obviously it does chamber the round easily though, it's Swiss ammo.
So how can that be

There is an answer.
Which brings us to a greater point.


Here's a few pics of a naked K31 revealing it's ingeniously simple, near perfect design.

Canuck, nope, all the measurements are correct. So I sat and thought about it for a while

Then it came to me

We are overlooking something because we are assuming. :banghead:

The 178 gr. GP11 bullet has a dia. of only .303 in.
Which means things like BC, sectional density, length all improve over a 178 gr. bullet in .308 dia.
Not to mention it's interaction with the barrel itself.

Think about it.

BTW;
I have mastered reloading GP11 brass. It's easy, no hydraulic.
Anybody interested in how?

Howdy boyz

I took the K-31 to the range today.
Ok, the bullet thing is easy. The difference in the bullet dia. from an absolute measure with a Starrett micrometer with measurement to .0001, on 5 pulled GP11 rounds measured at the widest spot is .3038 to .3046 in.
The difference between that and the Hornady .308 dia. is why the reading using the comparator tool comes out seemingly wrong, but in reality the readings are correct.

Yes, I have taken once fired GP11 cases and reloaded to a very high grade.

So here's the thing. Some special equipment will be needed. But once that is done it's a cake walk.

I have a photo showing the stuff. I'm using an RCBS berdan primer removing tool. The key to this tool is getting the bit properly aligned and to the required depth. The point on the bit is cut at an angle and must be correctly aligned. The depth of the bit is also critical as if the bit is not deep enough the primer ain't comin out. If the bit is set too deep it will damage the anvil in the case. Get those 2 things right and the tool works great.
Then to resize you just need to remove the decapping pin in the resizing die fob. Resizes the same then.
I got some Tulammo large rifle primers (berdan).
Then we need to press the berdan primer into the primer pocket.

The berdan primer is just slightly larger in diameter than the boxer primer .217 in. vs. .210 in.
I got an RCBS hand priming tool. Boxer primers are seated when it bottoms out in the primer pocket. But a berdan primer can be seated too far in and needs to be seated to a certain depth. So the hand priming tool needs one small and easy modification.
If you look at the photo you seem the squeeze handle has an adjustable set screw.
I drilled the handle and tapped it for a 10-32 thread and then put a jam nut on it and boom You now have a way to adjust the tool's stop point.
That's pretty much it. The rest is all the same.

To say it worked well would be an understatement.
I'll put up photos of the rifle I shot today.
The photo of the target is with the GP11 cases, Hornady 150 gr. FMJ, on top of 51.0 gr. of Reloder 17 @ 2785 - 2810 fps.
That's a 5 shot group @ 100 yrds off the bench, uninterrupted in 2 minutes or less without any shot being called out.
3 of the 5 are literally in the same hole.
Granted I was using a very sweet set of Swiss Diopter sights.

If you don't have a K31 ..................................... THEN GET ONE

Trent;
Really good info. The more I work with these rifles the more impressed I get with the ingenious simplicity of near perfect design and engineering, yet still totally sexy. In there own right they are like a vintage Ferrari.
So please do share with us about the different ogives. I want to know tooooooooooooooo

The RCBS decapping tool is rebust and works very quickly and neatly, no BS.
So I don't see how any reasonably mechanically inclined person could break one.

Yep, I know the GP11 is 174gr. was my misspeak.