Well, I have two modern pumps in 12 and 20, so I have not tried to cycle brass through them. In my Cimmaron 1878, I shoot brass. Read a lot of bad about the Magtech, so I went ahead and saved a few more pennies and bought 10 shells from Rocky Mountain Cartridge LLC. One, I can't say anything but nice things about their service and as my brother-in-law said, "you going to leave me these in your will?" They are stout. Since there is only 10 for now, I reload by hand, learned by watching youtube and then synthesized my own version that I thought made more sense. Only tools I have are a dowel with a rounded off nail in it and a dowel with an extreme dished end, a powder measure and a plastic mallet. They are a whole lot of fun and I am seriously thinking of buying 10 more as it takes no time at all to empty 10. If I score a single shot 12 gauge, I will totally be ready for when SHTF.
Realized did not address original question. I looked high and low for preloaded versions. None to be found that are not antiques. The fact that I load the, means it is easy, so easy an ape can do it.