I tried the Aguila minishells in my 870s on a lark. They're the #4 buck version- no luck. They'd end up backwards on the lifter if you ran the pump as normal. (vigorously) I have at least twenty sitting around waiting for the day I find an inexpensive 12 gauge SXS or O/U. Or a Savage model 24.

My 870 with a Vang-comp barrel produces the best results with Federal's 00 Flitecontrol loadings. My other 870 with a smooth barrel and rifle sights seems to like Winchester Super-X 00.

I'd stay away from the minishells unless you get the specific adapter that's made for the Mossbergs and such. I've not tried them, but your mileage may indeed vary.