What Shot Size To Use
A question that always comes up with TSS, is what shot size to use.
Given that the whole reason TSS is so much better is due to the high density of the pellet material - which enables one to go down in shot size in order to increase pellet count and pattern density, without losing any individual pellet penetration energy or to actually increase that penetration energy - the question of optimal pellet size of how far down in size to go, is a good one to consider.
The good news is, with the available ballistics software, it's easy to come up with what the optimum pellet size for a given situation is. Here's how I look at it - using turkeys as the game for illustration purposes.
You have basically two things to think about - pellet penetration and pattern density. You need both to kill turkeys consistently and cleanly. And there is a trade-off of those two things with each shot size and payload. For pattern density, I have a minimum standard of 100 in a 10" circle. For pellet penetration - 1.25" in ballistics gelatin. (These standards will be obviously different for other game birds and waterfowl.) Both these minimum standards must be met in order to know you will have a dead turkey 100% of the time you put the core of the pattern on him, at whatever range within those limits. The ideal shot size is the one where you max out on both those minimums at about the same time. Then you aren't dealing in overkill on one, at the expense of the other - since a shortage of either will hurt you. That's why I generally prefer smaller shot sizes in the smaller bores, and larger in the larger bores - to match up the pattern density and pellet penetration - thereby maximizing the efficiency of your rig and ammo.
Example On Choosing Shot Size
For illustration, let's say I have a 1-5/8 oz 20 ga load that goes 1150 fps MV. What's the optimum pellet size?
With number 8s, I know I can get 220 in a 10" circle at 40 yds. Using the .7 rule, that means I can get 100 in a 10" circle out to a little over 60 yds. And the 8s give 1.25" penetration out to 92 yds. So, I have a gap between the pellet penetration and the pattern viability of about 30 yds.
With number 8-1/2s, I know I can get 270 in a 10" circle at 40 yds. Using the .7 rule, that means I can get 100 in a 10" circle out to almost 70 yds.And the 8-1/2s give 1.25" penetration out to 82 yds. So, I have a gap between the pellet penetration and the pattern viability of about 15 yds. We're getting closer to the optimal size for the 20 ga.
With number 9s, I can get 310 in a 10" at 40 yds, so the numbers are 70+ for the pattern viability, and 72 yds for the pellet penetration energy. Those match up almost perfectly, with no gap between the pattern viability and pellet penetration. So, that's why I choose #9s for the 20 ga, for turkeys.
You can do that same exercise with any pellet size, payload, and game, to figure out the optimal pellet size for what you're trying to do.