.177 farmyard hunting....

[Blackrider]

Rhys, we'll have a chat at the Bash

[Muskett]

In .177 I don't think pellet shape makes any difference what so ever. Its completely dependent on shot placement.
In other calibres then weight of pellet might make a difference, but thats if it hits the right spot. Just deeper penetration which on a rat is way beyond the other side. Pigeon crop or feather plugging is the only real obstacle for the larger calibres at these low velocities. Maybe rabbit cranium, but not really.

There is very little hydraulic shock at these velocities/ft/lbs whatever the calibre. .25 might do something just because they are huge, big hole.

FAC then maybe.

Its shot placement that counts, and nothing else is going to fix a poor one.