Shotshell ounces are weighed ounces. Maybe you're thinking volume because of how presses drop charges by volume? Although presses drop by volume, that volume equates to a particular weight.
I weight every one of my payloads by hand. 711 grains. 1 5/8oz....590 pellets. 362 pellets per ounce.
#5 lead has 170 pellets per ounce. Less than half of the TSS pellets per ounce.
A #5 lead pellet is around 1.99gr best I could find. Depending on make up. Copper or nickel plated or hardening alloys (all used in most turkey loads) reduce that weight.
I just weighed a #9 TSS. 1.16gr. (I have a pretty good scale)
My hulls actually get trimmed and are more like 2 3/4" 20ga shells at the end of the day. But they still pack 1 5/8oz of shot.
The weight isn't the only factor of the formula. The tiny size and hardness make a huge performance difference. Its like a flying laser beam. The fact that it doesnt fracture or deform and how dang small the shot is make it something else..
I had some zip through a LOT of turkey body. I'd post pics but they aren't pretty...last year I shot one quartering to me nearly in strut. He wouldn't lift his head and his wing butt was basically behind his noggin....I had pellets go through the breast and break the breast bone. The biggest wing bone was blown to pieces. It's no joke.
These links may help make sense of it and explain actual penetration tests.
What Makes TSS So Effective? The key to the superior performance of Super-18 shot is the density. At 18g/cc (about 60% denser than lead), the penetration energy is so high that it enables one to go down significantly in pellet size, to greatly increase the pellet count and pattern density, while...
www.super18tungstenshot.com
The first link breaks down different shot and penetration.
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...
www.super18tungstenshot.com
That link explains why #9s are the way to go. In a nutshell, with a 300+ 10" circle. You'll still have over 100 in a 10" circle at 70yds and the penetration of the shot is still lethal.