The problem was the FMJ's. Honestly, in your situation I wouldn't have used the hollowpoints either. Really one of the best can be a .22 lr from a rifle to the head.
+1. On that topic, .22Mag would be even better. .17HMR would be better still if the ranges are under ~125m; it shoots flat as a laser beam at that range, but the little bitty bullets lose lots of energy at long range, so I don't know if I'd want to use one on a large stray dog farther than that.
The main problem with .17HMR is that I'd want a rifle capable of lightning-quick follow-up shots, but the round is no longer recommended for use in semi-automatics (see recent TFL thread), and I'm not sure if lever-actions like the Henry Varmint Express are readily available outside of North America. OTOH I'm not sure if .22Mag and/or .17HMR ammo is available either, so this may all be moot.