How much trouble is it to install a ball detent on an 870 barrel that does not have one? Also, do you know where I can get a 870 20 Ga. magazine cap W/Swivel stud and made for the internal magazine tube ratchet. Uncle Mikes has one listed [1800-5] ,but when you try to buy it you can only select the 12 Ga model. I have a cap W/ swivel stud and external detent but I worry it would back off if I forgot about it for a while. Ron