Used a Swedish mauser in 6.5, open sights, does the same job as a super-duper magnum with a 5-25x56 mega scope.
I've used most of my .303s for deer at one time or another.
I've got a nice 6.5mm Swede at the gunsmiths just now, and I hope to use that on a roe buck before the end of the season.
My eyes no longer deal well with open sights, and even in good light, I find it difficult to keep the fore-sight in focus; so any rifle I use for stalking has to be scoped.
I have and use a no4 mk2 sporter whilst I can use the open sights at targets in the day time it is really difficult if the deer is in shade or cover or the light is fading (my eyes are crap) so I have had to resort to a scope.