Unfortunately, if you want to pattern a shotgun right, you’ll need to shoot a couple different chokes and a few different loads. You can get by with just using the choke you have and experimenting with different loads, but you’re not going to realize the guns true potential.
I‘d try as many different loads as I could afford. Hevi-shot is a good load, as is Winchester long beard. TSS is probably the best load you’re going to shoot but those are VERY expensive. I remember reading a post on here that someone was shooting TSS loads out of a .410 and their kid killed a bird at 40 yards! That’s a hell of a shot for a .410 bore. I shoot TSS out of my .20 gauge and pay around $25-30 for a box of five, whereas that same load in a .12 gauge is around $50-70….sometimes more. I sighted in with birdshot then switched over to shooting every brand I could get my hands on at 40 yards. Ended up going with the TSS with the HevI-shot coming in second. I figure at over $6 per shot for my gun and only shooting one or two birds a year, a box will last me a few seasons, provided you pick your shot and kill most birds with one well placed shot.
If using a scope or a red dot, you could use plain old birdshot to get you on target like I did then switch to your best load to confirm it hits in the same place. One way to save money is to find one or two friends who also want to experiment with loads and each buy a couple different brands as you’ll probably only shoot a couple of rounds out of each box. There are some accomplished Turkey hunters on here so I’m sure you’ll get lots more good advise. Good luck. I’ll be following along to see how you’ve made out.