The sub-gauges are in for a tough road ahead. With no more bismuth or tungsten, a decent load really does not exist. Boss is working on a solid copper, I hope they can do it. Others have tried copper and could not get it to hold pattern. Steel just doesn't have enough payload in the bigger shot sizes. If you could buy up several hundred remaining bismuth shells to last you a couple years to see what happens in the future.
Tungsten is still available and being imported. Bought some from my supplier.
Also BPI has American made tss shot now. Same gairiffe high price they normally charge but it's available.
I either use a 1 oz duplex load of 8 tss and 4 steel or a straight 3/4 oz load of number 8 tss. Both in a 2 3/4 length hull.
I have two 28 gauges semi autos.
First is a TriStar viper g2 pro silver and a Beretta a400 upland.
Both have been great, super reliable, soft shooting and beautiful swinging duck guns.
I pick up the TriStar 9/10 over the Beretta when I take the 28 bore. Just not impressed with the Beretta and I'm a admittedly huge Beretta snob.
Wish Beretta would bring out a 28 bore in the a300 ultima line.
Can't speak to the over under or side by side guns. As I find them not to be of interest to me for hunting.
Above mentioned loads in my TriStar with either a Carlson's extended non ported cylinder choke or a skeet/IC choke will flat get it done.
With the 3/4 oz load of either 8's or 7's and a cylinder choke in good too 55 yards with the 28 bore TriStar.
Hope this helps OP.