I bought a "Remington Turkey Extra Full" choke to use in my Express and it patterned just fine. You can sometimes find some on Ebay pretty inexpensively.
I've had a Remington 870 Express for many years. Its a great turkey gun. I have the 22" turkey barrel. I added some tru glo sights to the rib. As far as my choke, I didn't get the best patterns from the Remington factory extra full. I bought a H.S. Strut turkey extra full choke and shoot Federal 3" #5's and can lay the smack down at 40 yards. I could probably shoot further but 40 yards is my self imposed limit. I put about 15-20 pellets in the kill zone at 40 yards with that setup. You may just need to experiment a little and find which setup works best for your gun. Good Luck.
i feel very strongly about this cuz i didn't believe it, but a comp-n-choke blows a kicks out of the water. unbelievable patterns, can't beat it. kinda hard to find but any of the turkey shows should have some. don't get me wrong, kicks makes a great choke, but for a 870 you can't beat a comp-n-choke!!!