Joe,
I still hunt with my Remington 870 SP with fixed full choke, (no screw in choke). I bought this gun new in the mid 80's and have shot many different loads out of it. The best lead loads were Federal copper plated 4s and 5s, 2 oz. Recently, I've been shooting the Heavy Shot "Blend", 2 oz. and it is a true 50 yard gun(if I wanted it to be).
Good luck, you have a great gun.