I'm using the TriStar semi auto.410. I go to ammo seek.com and buy a couple boxes at a time. Have around 350 shells now. I'm sure it would be cheaper to reload, but time is precious and money comes and goes.... One thing to think about with a .410 pattern is the string of the pattern. On paper a pattern may look good, but all those pellets aren't getting there the same time. I had a piece of sheet metal set up that could spin around. At 35 yds the pattern was looking good. Then I looked closer and the metal had holes coming from both directions. So the pellets got there after it had spun.... Really surprised me. I've heard the string can be 8-12 feet long. Lots of pellets trying to make it out a small barrel. Some say 2 1/2" shells pattern better
You are right about the shot string. Another thing that happens is the shot in front takes the most air resistance so it slows faster than the shot behind so the shot behind will catch up with and may run through the shot in front spreading the pattern.
A lot happens in nano seconds.
It seems like around 1250 fps usually does best.
I have a friend that turkey hunts with a 410 and number 9 tss shot. He says the tss is amazing in what it will do.
At around 8 bucks a shot it would need to be good.
I have shot my contender a little more at cans and cardboard and it looks like about twenty yards will be my limit with this barrel.