309JDJ or 308 Bellm will get the job done nicely, even on big deer. There are smaller rounds that will get the job done, but these are my choices. I don't consider the 7x30 out of a shorter barrel as a 300 yard gun...but I do have a 24 inch 7x30 that is pretty good out to 250 or so. then again, I don't really ever shoot that far.
regards,
Graycg