Now I want to make it clear that I'm not an expert, but I want to share my limited observations and see if it has any validity or common experiences.
I’ve been reloading for about 5 years
I’ve reloaded for 2 straight walled cases, the 45-70 & 475 linebaugh, along with 6 bottle necked cartridges; the 270 winchester, 30-06 springfield, 300 win mag, 338 win mag, 375 H&H, and 375 ruger.
The only one that has caused me problems is the 375 ruger. It is also the only one I have reloaded for that has a very level shoulder. In other words, the shoulder angle is more horizontal than that of most other cartridges.
The problem I was having is that when seating a bullet, the case would want to bulge frequently. I attribute this to the downward force having more pressure pushing out to the sides instead of down, do to the angle of the shoulder instead of the force concentrating more downwards like it would on a steeper shoulder.
Now the 416 rigby has a very horizontal shoulder and I never hear anything about the case bulging when a downward force is put on neck of those cases, so maybe it is just dependant on the brass. But I was wondering if anyone else has observed this phenomenon of cases bulging when seating bullets in cartridges where the shoulder is at more of a horizontal angle.

It has happened to me and I've seen happen to others. It is often caused by the case being pushed too far into the seating die body. Another cause is excessive neck tension on the bullet during seating. I would agree that the forces acting to bulge a 'more horizontal' shoulder would be far greater than say on a 30-06 shoulder.

I would bet you a Yankee Dollar that your expander button needs to be about .001-.002 larger. A simple thing you might try is taking an old cleaning brush and wrapping some OOOO steel wool around it and polishing the neck inside for about five seconds per case. It's a benchrest thing I learned about twenty years ago.
Consistency and conformity are the key words to an accurate rifle. Uniform the cases, cut the primer pockets the same depth, and trim them religiously.
By time you turn sixty you can learn a lot if you pay attention and take good notes.

Rich

yeah it was the dies. I bought a different brand and it got better.
steel wool is very handy. I had to use some in the chamber of my remington shotgun so that it wouldn't lock up after firing

gohip2000

You are correct in that the 416 Rigby does have an abrupt shoulder and with some cases this cartridge can show up the same problem you have had with your 375 Ruger. Many reloaders of the 416 cartridge seat bullets in smaller increments rather than just work the press handle all the way in one action. All depends on the particular brass one uses but particularly important I would think after annealing cases.

To much crimp. There is a crimper in the seating die as i am sure you know? Or as said the expander maybe to small. .0015" under bullet diameter is good. You may want to seat the bullet first, then in a separate operation, crimp the loaded round. This helps reduce the overall pressure when seating the bullets. When crimping, make sure all brass is trimmed to the exact same length. Chamfer the case mouth.

Back your seating die out one turn and then adjust the seater plug to get your desired OAL.

thanks for the advice. trust me, it's not that the die was set wrong. they crushed without trying to put a crimp. I know it was a matter of the expander ball being too small, brass neck thickness being high, the angle of the shoulder, and probably the shoulder being too thin. since I bought RCBS dies the problem has gone away. it was the hornady dies. there is still a problem of the expander ball not wanting to come through the neck without extreme force, but that gets better after the cases have been fire about 3-4 times and trimmed. then the brass starts acting normal

I got a set of hornady dies for a buddies 7wsm. The expander ball measured .283 yet it left about .007-.008" grip inside dimension of the mouth after sizing. I never did take a measurement to see how small the case mouth was getting during resizing (w/o expander in die). All I know is it really had to be working that neck area hard to get that much springback. Loaded runnout when seating was terrible too. Funny thing is the result was that his factory BAR began shooting 3/4" groups with several recipies coming from these dies.
I should probably send them back to Hornady for a hone job but for now I can alleviate the problem a bit by making several plunges over the expander when withdrawing the case to open it up more. He doesn't shoot the gun much and the accuracy is good so we'll probably leave the whole deal as it lies for now.