7.5 Swiss Reloading issues

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AirForceVet

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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
 
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
 
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.
 
AirForceVet said:
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.
Click to expand...
Did you check case length after sizing?

AirForceVet said:
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?
Click to expand...
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.

AirForceVet said:
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?
Click to expand...
I agree with the others, you are likely not getting the bolt completely closed.

DiMP said:
I noted when I went from my K11 to K31 with the same reloads, the lands appear to be much closer on a K31.
Click to expand...
Yes, the K31 has a much shorter throat.


Mark
 
Lees instructions say to adjust the die until it touches the shell holder when the press handle is all the way down and then raise the handle a bit and give it another 1/8 to 1/4 turn down
Some presses will “cam over” which gives repeated and full sizing
My Lee progressive doesn’t cam over so I just set it to touch the shell plate and that’s it
If your having to use a lot of force to size it’s possible that your rifles chamber is a bit big or maybe your die is sizing the case too small
I had a 7.5 French die that Lee replaced because I couldn’t size it properly, they figured it missed the final polishing and it was too tight and sizing the brass too small
I could barely size the case with that die too
I’d be measuring the length and dia of a case you sized compared to a factory round plus measure one that you fired in the gun and not sized yet
Should be able to figure out what’s going on
 
I’ll ask the question, because has this happened to me? Yes!

Did some other calibre brass accidentally make it into the 7.5 pile and go through the 7.5 die?
 
Either the bolt isn’t closing all the way or you have a serious headspace problem. I suspect the former rather the latter. Have you detail stripped your bolt yet? They are unique but not particularly difficult. Could be some gunk in extractor channel. I had a Winchester model 12 which, after 80 years of running just fine, decided to stop going into battery. Turns out it was gunk buildup behind the outboard extractor causing it to stand proud and catch on the ejection port. That gun is complicated, the Schmidt Rubin’s are a walk in the park on contrast. And It’s my last post of the day. As a newb, I only get 3. Hope you liked it :)
 
AirForceVet said:
Does anyone else find the resizing requires a lot more force than 308 or similar brass?
Click to expand...
You know what, I was resizing some 7.5x55 S&B brass the other night and thought to myself, this does feel much harder to resize than other brass. Like you, I am newer to loading this caliber however, I am not having any issues with it. I am using hornady dies.

I have realized that the k31 has a relatively short throat.
 
The die was set per Lee instructions. A 1/8 turn more and the shoulder is bumped too far back (.006). The die is very tight on the down stroke at about 50 percent in. I’m thinking I may have a poor die set and Flitz polishing the inside of the resize die.
I had several earlier rounds that I made without bumping the shoulder back and didn’t have a problem. I read that the shoulder bump (datum line) should be about .002 - .003 less than the fired brass. That assume the brass is perfectly fire formed to the chamber. Other readings say only to push it back enough to fit. The problem is the die works the brass by squeezing it down and then stretching it longer in the up stroke. My brass was coming out of the full size die longer than it went in. I ran it again with the die set to cam over a bit to get the .003 bump. I feel like I may have gone too far. The K31 is finicky with a short chamber. The reloads may work in a different K31.
I was hoping that another K31 reloader has delt with this issue.
I appreciate all the help everyone has contributed.
 
5five6 said:
Either the bolt isn’t closing all the way or you have a serious headspace problem. I suspect the former rather the latter. Have you detail stripped your bolt yet? They are unique but not particularly difficult. Could be some gunk in extractor channel. I had a Winchester model 12 which, after 80 years of running just fine, decided to stop going into battery. Turns out it was gunk buildup behind the outboard extractor causing it to stand proud and catch on the ejection port. That gun is complicated, the Schmidt Rubin’s are a walk in the park on contrast. And It’s my last post of the day. As a newb, I only get 3. Hope you liked it :)
Click to expand...
I haven’t and that is an excellent recommendation. I off to the range to test again and asked a friend to bring his K31 to test my reloads.
 
I had the same issue. It was about the bullet seating dept. In some cases the bullet would get stuck to the lands and get pulled out when i pulled the bolt back as well.

I solved it by creating practice rounds at home, first i would adjust the seating to make sure the bullet wasn't shoved too far put the lands on the lands the i would make a cartridge with primer but no powder to check if the primer would strike.

It really comes down to bullet geometry, the gp11 bullets seem to thinner on the front
 
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