Tell him I call bull$hit. I can hit out to 300 with the 7.5". Not saying it's deadly at that range, but I can hit steel, with boring regularity.
Next time I'm out, I'll take it with me. I'll keep the targets. I'll give you groups from 25, 50, and 100.
The problem is FPS. You need to keep the projo speed up for the round to perform like it's designed - fragment. Once it drops under a certain FPS, it won't fragment. I'll find the precise data sometime, because I've got that info saved and stored. Basically, on a 7.5", you're only "effective" out to about 75 yards. Beyond that, no fragmentation.
There's also a pretty big drop in speed between 11.5" and 10.5".
20" down to 16" down to 14.5" down to 11.5" - not alot of drop in speed, but almost consistent, inch by inch. It falls pretty far when you get down to 10.5". The step down between those two lengths isn't as consistent as the other inch-by-inch tests.