I would use a tube recommended for steel or heavy shot. My cousin blew the choke tube out of his gun last year, I shot an 870 12 gauge and use a stardot extra full .668 approved for heavy shot, using HEVI 13 3" shells with 1 3/4 ounce of 6s put 166 pellets in a 12 in circle at 42 yrds, had 39 head/neck hits in the turkey target and 317 pellets in a 20 inch circle. They are high though, paid 26 bucks for a box of 10 but on paper the doubled my pellet count.
Ray