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You're setting the shoulders back too far and probably loading a bit hot for good case life. Excess shoulder set back leads to unneeded case stretching. The 99 locks at the rear and tends to spring more than front locked rigs so that adds to the case stretch on each firing.
By reducing the amount of case stretch we produce we can greatly extend case life. All a Wilson type 'drop in' case gage will tell you is if your ammo falls within the SAAMI minimum and max lengths and is helpful if you want to swap your reloads around other rifles but it won't tell you a thing about how well your ammo actually fits your specific riflle.
Simplistic die set up by the numbers will make ammo that will chamber and fire but it can't be very precise. Setting up a sizer properly requires something that can give us exact information, something like Hornady's easy to use cartridge "headspace" tools that mount on the jaws of a precision caliper are good. Use that to find where fired shoulders are and then resize to restore the shoulders back to where they were, or just a tiny tad shorter. Doing that will greatly reduce the incidence of head seprations in any rifle. My cases die due to neck or body splits, I've not had a head seperation in almost 50 years of reloading.
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