People! Please! Let me clarify!?
If the op asked about let's say Lee Enfield? I would still question the op's motivation, how can someone present on this board not be aware of capabilities of a caliber that has been around for about 100yrs? Now was he asking about gun in .243 or lesser caliber most of you would likely politely or not, point him to oh so many threads that has been started on such subject in as long as this forum been running. Am I wrong?
In the end it's not about the size of the bullet, it's about how comfy are you with the gun you carry, if you can consistly put rounds in the black at 100m on the range you should have no problems taking down any animal, armed or not, the fact someone asked the question in first place tells me that someone has limited knowledge of animal anatomy, there are plenty of source on line to remedy that. Read, learn, ask intelligent questions.
Now, op, you really should sell or trade the rifle in question (I'm willing to help you out

) and
get yourself something more capable, like Lee Enfield