7.5 Swiss Reloading issues

[jethunter]

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

Offhand I'm wondering if you bumped the shoulder too far back. .003" is quite a bit if the brass was already at or below minimum

Is it possible the bolt is not fully closed...? Like for instance your bullet is jamming on those famously short, tight, and picky k31 throats?

I much preferred loading for the K11.

 

[AirForceVet]

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.

Ding, ding, ding winner! Thank you. Slamming the bolt closed fired each round. Even when the bolt appeared fully closed, and the trigger released, the pin must have a safety to prevent primer strike. Closing the bolt hard showed the lands were touching the round. I’m going to reset the seating depth.
Thanks vert much.

 

[AirForceVet]

Offhand I'm wondering if you bumped the shoulder too far back. .003" is quite a bit if the brass was already at or below minimum

Is it possible the bolt is not fully closed...? Like for instance your bullet is jamming on those famously short, tight, and picky k31 throats?

I much preferred loading for the K11.

The brass was once fired; fire formed in the K31. The problem was the rounds were proud and just touched lands enough to prevent full bolt closure. I had two lots of Hornady. The second lot was .008 Bullet base to ogive different and I didn’t test the seating depth, thinking they were identical. It’s shooting now.

 

[bearhunter]

Does anyone else find the resizing requires a lot more force than 308 or similar brass?

It's your FL resizing die. Just because it's pushed the shoulder back .003 at the datum line, does not mean it's properly sizing the rest of the case. I've also had similar issues with Lee dies, most recently on the 218 Bee.

You've got a set of Redding dies on hand, and you know they work.

On my Lee 218 Bee FL resizing die, I had to grind the bottom off the die so it could be screwed down further, so I could properly size the case to fit into the tight chamber on my Martini.

I've had this issue with other dies as well. It happens.

I posted this before reading your last post, but you shouldn't have to "slam" the bolt into battery to get it to lock properly. K31 actions are smooth enough, and tolerances are set so this shouldn't be an issue.

Your Lee die isn't sizing something on your case properly, and by "slamming/forcing" your bolt into locked battery, you are completing part of the sizing process in the rifle's chamber.

 

[AirForceVet]

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

I did this on my first lot of bullets. I use the same bullets for my 308. Everything was fine until I opened a new box of Hornady. The product numbers and specs are the same. The old bullets were from the 1990s and the ew from 2015, the actual bullet base to ogive is .008 difference. The seating die was not changed when i started using the new lot. I have old Sierra Matchking 150s. Old and current lots, I picked up at an auction. Same issue. The specs are slightly different between old lots and near current. I took pictures and feed them into AI for comparison. The AI could spot a difference in the ogive and geometry. My eyes couldn’t.

Both Hornady and Sierra have changed ogive/nose geometry on some MatchKing bullets over the years. Who knew.

 

[Percussianprimer]

OAL very well could be your problem. Had the same issue and seating them deeper by 60 thousand solved the problem for me.
Good luck.

 

[Irons78]

I did this on my first lot of bullets. I use the same bullets for my 308. Everything was fine until I opened a new box of Hornady. The product numbers and specs are the same. The old bullets were from the 1990s and the ew from 2015, the actual bullet base to ogive is .008 difference. The seating die was not changed when i started using the new lot. I have old Sierra Matchking 150s. Old and current lots, I picked up at an auction. Same issue. The specs are slightly different between old lots and near current. I took pictures and feed them into AI for comparison. The AI could spot a difference in the ogive and geometry. My eyes couldn’t.

Both Hornady and Sierra have changed ogive/nose geometry on some MatchKing bullets over the years. Who knew.

I use Hornady bulk 150gr fmjbt and Barnes 175gr matchburners, both have secant ogives.

 

[mbogo3]

I load 150gr Win PPSP seated 2.893" in my K-31 using Redding dies [go figure] with 44gr 0f IMR 4895 in PRIVI brass and a Fed mag primer.
.652" 3 shot benched group at 100 yards. 6X Leupold in Swiss steel mts. Tilted a mule deer with it at 150 yards.