I still have some that have to be 10 years old - they work great, but they have been stored in a box in their bags and without light getting to them... Other than that I really do not know....
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Keep on Shooting Muzzleloaders they are a Blast
I used up a bag of Hornady 44 cal Mag sabots last Spring which were 17+ years old and they shot great. I'd avoid heat/cold and UV light and if you do, your grandchildren should be able to use them.
I had some Knight sabots for back when they first came out with them must be around 15 years ,my friend just getting into muzzleloading bought a Knight big Horn and I gave him some bullets and those sabots and he got 1.5 inch for his first group. Like sabotloader I store them in airtights [zip lock] and ammo cans so limit air and no light I suspect that if you left them in sunlight very long it would cause deteration. Lee