playin' hookey wrote:
My understanding is that penetration is equivalent to 4 sizes larger lead shot, so #9 TSS gives penetration of #5 lead.
As for comparing TSS (18g/cc) pellets vs lead (11g/cc) a TSS pellet will have about the same penetration energy as a lead pellet 5 sizes larger. So, a TSS #9 pellet will penetrate into soft matter at approx the same depth as a Lead #4 pellet. However, in real life scenarios, on real birds, the TSS will actually do better vs lead, because of hardness. TSS will break bones better, or any other hard material, because of its hardness and lack of flattening out when it comes into contact with any surface. Therefore, for the purposes of killing turkeys, shooting a 2 oz load of TSS #9 is superior to shooting a 4-1/2 oz load of lead #4s. And looking at it from the opposite direction, what that means to me and my turkey guns/ammo combos, one has a more effective gun/ammo combo with my .410 and 7/8 oz of TSS 9s, than with a 12 ga 3" 1-7/8 oz load of Federal lead #4s - measured by number of pellets on target and the penetration energy of those pellets that strike the target.
For illustration, here's a comparison of pellets of various shot material. Let's say that each pellet is going 1100 fps (muzzle velocity), at sea level and at 70 deg F. Here's the distance each type pellet will give you 1.25" of ballistics gel penetration, as well as showing the number of pellets per ounce. When you think about the penetration per pellet along with the number of pellets available to penetrate the target, these numbers will illustrate why density makes such a huge difference in a shotshell's performance on fowl.
8g/cc Steel #2 (123/oz) – 45.7 yds
11g/cc Nickel Plated lead #5 (174/oz) – 60.4 yds
12g/cc Hevi-13 #6 (208/oz) – 60.4 yds
15g/cc Fed HWT #7 (220/oz) – 81 yds
18g/cc TSS #8-1/2 (300/oz) – 84.5 yds
In addition to penetration energy and pellet count, there is a 3rd factor that doesn't show up in the math - patterning characteristics. In a nutshell, the denser and harder the shot material, the better the pellets will hold together in a pattern.