In my limited experience, 38 caliber seems to be the lower limit where I draw the line. It isn't so much the speed of kill but the amount of blood let out for tracking. This appears to be dependent on bullet shape and at 38 caliber it seems even a round nose lets out an adequate amount. Add a flat point and the exit seems to bleed better.
The 35 calibers may be adequate but my experience there is limited to handguns. The lower velocities and hard bullets have not been impressive as I would like. Lighter 158 gr bullets like I tried may have been a factor too, 180 gr jacketed bullets have been more favorable the couple times I used them. I imagine a like weight SWCs would perform similarly. I would like to try 180-200 gr bullet in the 35 Rem as it should rival jacketed bullets. So far, my meager search turned up round nose bullets which I don't think provide enough of a bloodtrail. A mould with a decent flat point will become a search subject at some point I'm sure.
