7.5 Swiss Reloading issues

[AirForceVet]

I’m reloading 7.5×55 Swiss for my K31 and have loaded about 100 rounds so far. After this problem, I’m hesitant to load any more until I understand what went wrong.

I made a batch of reloads in which the firing pin apparently did not reach the primers. Using a comparator, I full-length sized the cases to set the shoulder datum back approximately .003” from fired factory Sellier & Bellot 7.5×55 brass.

I measured the bullet’s jam point with a 147-grain Hornady bullet, then loaded a small test batch at varying seating depths to determine what my K31 preferred.

I loaded 50 rounds. The first two fired normally. The next nine failed to fire, and none of those nine primers showed any firing-pin impression. The bolt appeared to close fully and the trigger released normally.

Load data:

147-grain Hornady bullet
IMR 4064 — 41.0 grains
Sellier & Bellot 7.5×55 brass
Jam CBTO — 2.387”
Starting CBTO — 2.357” (approximately .030” off the lands)
CCI 200 primer

I’m using a Lee full-length 7.5×55 sizing die, Redding Imperial Sizing Die Wax, and a hand priming tool.

One thing that concerns me is the amount of force required to resize the brass. I also reload .308 Winchester for precision shooting using Dillon dies on a Dillon 550. The .308 cases resize easily. The 7.5×55 cases require roughly four times as much force to size. I have to stand during the downstroke, and every time I size one I’m concerned that I’m going to stick the case.

The Lee die is clearly marked 7.5×55 Swiss, but this amount of sizing resistance does not seem normal.

I’m particularly interested in two questions:

1. For those who regularly reload 7.5×55 for the K31, is unusually heavy sizing force typical with fired S&B brass and a Lee full-length die?
2. What would cause a K31 bolt to appear fully closed and allow the trigger to release, yet leave no firing-pin impression at all on the primer?

I’d also appreciate recommendations for the best sizing die/setup for loading accurate K31 ammunition.

I’m especially interested in hearing from people with hands-on K31 reloading experience who have encountered anything similar.

Thanks
Mark

 

[DiMP]

I noted when I went from my K11 to K31 with the same reloads, the lands appear to be much closer on a K31. With this in mind, I will be setting the bullet back further than I previously had (waiting for a new type of bullet to arrive before adjusting anything). Now, not sure this would be any of your problems because you note you are already seating back from the lands, but just a note for others I guess. I also noted on it that there was a few times I didn't run the action forceful enough and the bolt handle did not lock all the way forward. A few times it still allowed the firing pin to drop, but with only the ever so slightest mark on the primer. I noticed this and gave it a little hit forward, re-c0cked it and it fired

 

[mephisto002]

I don't think your bolt is fully closed.

The same happens to me when the cartridge OAL length is too long, or the brass is not fully resized.
The bolt closes, and fires, but the firing pin doesn't reach the primer.

 

[mbogo3]

You need 7.5x55 K31 dies.........they have tighter chamber specs. Redding and I believe Hornady makes specific K31 dies.

 

[mephisto002]

I use RCBS dies and they work perfectly, you just must know how to adjust dies in general. I don't believe there is anything wrong with the Lee dies.

Never heard of special K31 dies.

 

[Donkin]

Its your dies, I tried Lee dies to start, and had the same issues, got some Redding dies and the problem was solved.

 

[Snider shooter]

I doubt you have broken a firing pin. Likely bolt isn’t fully closed. The Swiss straight pulls are made to be worked with some force. I use Lee dies without any issues. Lee dies are known for being on the small side. The Hornady K31 set is a small base die set. Nothing special. Only set I know that is marked that way. Marketing gimmick.

 

[mmattockx]

Using a comparator, I full-length sized the cases to set the shoulder datum back approximately .003” from fired factory Sellier & Bellot 7.5×55 brass.

Did you check case length after sizing?

For those who regularly reload 7.5×55 for the K31, is unusually heavy sizing force typical with fired S&B brass and a Lee full-length die?

I've not noticed any difference between 7.5x55 and any other similar sized rifle cartridge. My 7.5x55 dies are Redding, but I have not had any issues with many sets of Lee dies in other calibres.

What would cause a K31 bolt to appear fully closed and allow the trigger to release, yet leave no firing-pin impression at all on the primer?

I agree with the others, you are likely not getting the bolt completely closed.

I noted when I went from my K11 to K31 with the same reloads, the lands appear to be much closer on a K31.

Yes, the K31 has a much shorter throat.


Mark

 

[mephisto002]

Adjust the dies, so that the shell holder "kisses" (touches) the base of the dies, and your problem should be gone.