That was my thought too 223 brass, but a longer neck then 17-223.Yes the 17 TAC is a really nice cartridge for Groundhogs and Coyotes in my neck of the Woods!
Im getting 4224 fps with Berger 25 gr Target bullets and 3950 fps with Woodchuck Den Gold 30 gr Boattails!
My rifle is a Rem 700 with Lilja 26 inch Rem Varmint contour 1-9 Twist and man does it Hammer!
My last two Groundhog Seasons the 17 TAC was what i used on my longest two kills. 548 and 471 yards.
I like the fact that it uses 223 brass to make the 17 TAC.
Plus any fast 17 caliber is Hard to beat on Varmints and Predators !