You already have a decent cartridge there.
The Model 100 is one of the few rifles I clean anytime I shoot it. If the gas piston rusts, you will not be able to open the action (which you must do to disassemble the rifle)
Please note there WAS a safety recall on the 100- firing pin could break, wedge in the forward position, resulting in full auto fire. Simple fix, different firing pin. You can call Winchester, they can check to see if yours has been fixed- or remove mag, turn rifle over so you are looking into mag well, open bolt, look for a letter stamped inside the receiver above the bolt.
I will be hunting opening day with my Dad's Browning in .243.
What we have here is... failure- to communicate.