231 is way too fast for your 357 magnum. You won't be able to use full power loads with it. Unique is about the most versatile. 231 will work for everything else though. If you bought 2 powders, 231 or tightgroup and a magnum powder like 296. you would be covered.
Seat it deeper, just until you are .020 shorter than into the lands as you are now. Reduce your load if you think you need to. On the bottom picture, you look fine. If you want to seat into the lands this will eliminate headspace in your encore as it does in a contender. Adjust your sizer die...
If they are RCBS dies, send it back and they will replace it. They are the best Customer Service on the planet. No, I don't work there, but they have fixed every loading problem I have had in the last 45 years! Lyman, not so much. Still fighting with them.
The only negative is case capacity. Try other depth settings for accuracy, all barrels are different. You can have a gunsmith cut you a new throat pretty easily if you want to though.
Try marking the entire cartridge with sharpie. Chamber it and look for rub marks. This will tell you where you are tight. Look especially for rifling marks on the bullet.
I'm an old timer, Hodgdon started out selling surplus GI powder. IMR bought Dupont which started out making black powder. Hodgdon does not make powder they sell it. They also own IMR now. I use all brands for one thing or another, even those Johnny come lately Accurate Arms guys. Don't be afraid...
Make sure you have not bumped the shoulders too far back and thereby creating too much headspace. This will cause the firing pin to push the case forward in the chamber, not firing it.
Some powders are the exact same formula like W296 and H110. They are made by the same manufacturer currently. However, it depends on the age of each powder. Some of the older formulas are still different between them. I wouldn't mix unknown ages of powders.
Segregate your brass and only use one headstamp, whatever you have the most of. Keep your brass separate for each rifle, this will simplify your loading headaches.
You have a 200 dollar die in a 20 dollar press. Use quality to make quality. You should not need to use the expander ball in an s die. measure your necks in a fired case and adjust the bushing size to get your desired neck tension. Trying to neck down too much will show erratic results. Try...
Like you have heard already, separate it! If I had the most of any brand, I would use only that. Lapua is king. I use only one headstamp, never mix, why, it is too much work to keep em sperated. Buy some more Lapua and don't look back.
Flash hole deburring tool is for the inside the case hole through the primer pocket. Flash holes are punched through and need to be cleaned up on the inside. Primer pocket uniformers are for the primer pocket to uniform the pocket. two separate tools. You will need a case trimmer too. I like the...
Are you saying a tenth of an inch! As in .100? That seems excessive, I would look at the die, maybe it is dirty or has some debris? Take it apart and clean it, then retry. Keep us posted.
I think most die makers will do this for you. You still have to adjust though. The advantage would be in the neck, they would resize to your chamber...not the SAAMI
Your chamber is bigger than your dies, not a problem other than you will be working your brass a lot. Use the bent paper clip tester on your brass to check for separation as it gets more loadings on it.
If you are loading rifle in batches, I like the Satern caliber specific powder funnels. Loading blocks, I use MTM universals, but there are better ones for specific calibers. If you are loading military brass, a primer pocket swager is handy. I use a Lyman power trimmer. Neck turning tool...