I have a rifle I picked up with a fair amount of handloads. One in particular shoots great. It utilizes H4831 powder and loading info shows 1998 as the loaded date. Just wanted to see if the recipes for powder have changed much and I need to start over, or if I can just try to start with what has been working?
What calibre, what bullet weight and powder weight, meaning with more info we can look in our reloading manuals and give a better answer.
I have been reloading for over 47 years and any powder can vary from lot to lot but has to stay within a given range.
If the ammunition is loaded close to max load you could reduce 10% and make a new work up load especially if you change primers, brand of bullets, etc.
What do your fired cases look like, my biggest concern would be how many times have the cases been reloaded before you got them.
My son came home two weeks ago and we fired my 30-30 with ammo I loaded in 1986. And I will reload these cases with the same load I have used since 1982.
These 30-30 cases are loaded near max but the 30-30 is only loaded to 38,000 cup or 43,000 psi and my primers are protruding.
Lay a straight edge across the base of your fired cases and the primer, if the primer is protruding even the slightest amount and not flush with the case its well below max load.
Once you give us more information and know more about the load and estimated chamber pressure we could give you a better answer.
If I switched to a different brand of case, primer, powder or bullet I would start low and work up.