I have a Remington V3, and want to use it for predators. I have Remington flush chokes in full, IC, and M, Remington predator/turkey P/N 19171 (.665"), Carlson's Coyote P/N 30044 and Waterfowl MR&LR P/N 07260, and Kick's Gobblin' Thunder P/N GTREM12G (.655"). I will be testing #4, #2, BB, 4B and maybe 00B loads. At what distance should I be testing patterns at, and what size target should I use?

If it were me, I'd pattern at whatever distance I hunt at, i.e.; if your hunting spot has a max range of 55 yards, pattern at that distance. You know good and well if a load patterns to suit you at 55 yards it dang sure will pattern at 25. As far as the target size, find a paper target of the critter you're going after (coyote, fox, etc.), and pattern in the kill zone of that target. What that will accomplish for you is this: in your mind you know that you can hit a known size critter at a known yardage. So, when you get to where you're going to hunt, you can establish a rough estimate of the range and feel confident you can hit what you aim at, at that distance. I do the same thing with deer hunting: I sight my rifle in for the area I hunt and so far have had very good luck making "sure" shots out to that range.

My 2 cents only, and worth exactly what you paid for them

Mac

Sound advice Mac.