misfit, I have hit 40+ pound dogs and they have never gotten back up with a 17 remington. the 25 grain Hornady V-max and Berger Varmint HPFB have never failed me. My hunting buddy with his 22-250 Rem has hit 35 to 52+ pound dogs and they have never gotten back up. heart and lung shots bring dogs down and they do not get back up. I have used neck, head and heart/lung shots with 17 Rem, 22 Hornet, 223 Rem, 223 WSSM; without failure they go down with one shot and never get back up. I must be using the "Magic" slugs. Hornady V-max, Speer TNT, Nosler Ballistic tip, Sierra BlitzKings. nothing I fire at a coyote has failed to work if I hit the dog. most of the time with a 17 Remington they crumble mid stride and are history.. with my hunting partner's 22-250 with 40 grain V-max have brought down more coyotes than I have with my 17 and 223 Rem combined. he has changed to factory Winchester 40 grainers. nothing fails in his 22-250. in fact we found the Sierra 40 grainers are too explosive; they rip the dog apart and ruin hides.
I shot a coyote with my 257 roberts from 350 yards with a 60 grain flat point (25-35/25-20 slug) and the dog exploded.. ripped it so badly I have not used that load ever since. use 75 grain V-max now for less destructive results and I have loaded the round down to starting loads and it seems to down coyotes quite well.
I am totally unimpressed by the whole 6MM family.. I owned a 243 once and I could never get the dang rifle to shoot right.. I have repaired many 6 MM rifles and have seen ugly to unbelievably bad shot groups.. I just do not trust the 6 MM to be accurate. I have had over 50+ 6 MM bores in my hands and not one of them grouped under 1.75" at 50 yards.
peace through superior firepower....
Quite simply, you have crappy 6mm rifles then. It is the ballistically superior projectile. The 6PPC may be the most efficient round in the world. The 6mm is reknowned to be the most accurate projectile. Now if you don't have a good rifle, it doesn't matter what caliber you use, it won't shoot.
But as far as your feelings on 6mms, they are just feelings and the evidence suggests that they may be skewed, significantly.
I shoot most of my coyotes while working on the ranch so shot angles are not always perfect. I think anything works well on a broadside coyote, but the 6mm's with a 70gr or heavier bullet will handle tough angles and still leave a dead dog. I haven't had those results with a 223 or 22-250 and 50-55gr bullets. The 243-6mm's have been the most accurate rifles I've owned and done a great job on a couple hundred coyotes with 70gr ballistic tips, 75gr V-max, or heavier bullets. Most have been with the 70 or 75gr bullets, but I've tried most all of them.
I've shot lots of coyotes with the 22 cal rifles and am building a 204, so It's not that I think that they don't work. I just want plenty of penetration from any angle. I shoot yotes with a 6mm & deer with the 264 win mag - 7mm Rem mag range of rounds . I believe in having enough gun for tough conditions even though lighter calibers work great with a well placed shot. I like exit wounds on big game and coyotes that fall in their tracks without one, even if bone is hit.