Too big, no, but it is alot more than is "needed". I have a couple of 300 WSMs and use 150 gr ballistic tips in mine. I killed a doe a couple of weeks ago at 30 yards+/- and wasted almost the whole front end due to tissue damage. She never knew what hit her, but it was a mess. The only reason that I took the gun hunting was it was new, and I had never killed anything with it. It is definitely "bloodied" now.

Why 180 gr and not 150 gr for your 300 WSM?