No Hope For Me
Its going to have to be much better than a 4 inch group to make me happy. it will have to shoot a 1.5 inch group or better at 100 yards to go hunting with me. a 4 inch group at 100 yards is a Miss at 200 yards and would be pretty much unusable at 300. I have shotguns to do better than that. not to be insulting but if you're sporterized Mauser Is shooting 4 inch groups at 100 yards there is something wrong with the gun or the ammo or the shooter.
I have no problem with a 7 mm Mauser. if my barrel was any good I would keep it that way. however I can make it a 260 Remington for about 30 dollars as I already have several of the barrels. I also have over 1000 rounds of 308 brass that can easily be formed to 260 Remington. the 260 Remington shoot flatter and kicks a little less and will be cheaper for me to shoot.
If you're having primer troubles it's not the brand of gun or who made the gun, it's an issue with either the barrel or the ammunition. if that ammo works fine in 1 gun and does not work correctly in another then you likey have a barrel or chamber problem. you would likely see primer issues if that barrel was on any other gun with the ammo you have.