Ive noticed that American made 9mm's have a taper at the base but foreign made ones have a straight case.... Why would this be?? If I buy a brand like Remington or Winchester it wont fit my Medusa, but Seller & Bellot and Fiocchi fit great?? (Exception: I have a old box of 40's-era Remington 9mm and it fits???) Whats the deal??