Curt14

I recently purchased a SBE2 (slightly used - less than 5 boxes had been shot through it) and shot it for the first time yesterday using Estate 3” magnum 3 shot. I have had the shells for around 20 years, but have always been kept in a cool dry place in my garage. I had 2 hulls separate from the bases yesterday. I had been shooting the same ammo for years in my Remington 870 Wingmaster and never had a shell separation. As I am new to Benelli, was wondering if anyone has had a similar experience. Is this a shell problem or gun issue?