Which 300 gr. bullet are you using? The .430 or the .452? The .430 or 44 cal. has better sectional density. I agree with Cayuga though. No matter which one you are using they should do the trick if you put them in the boiler room. Check ouy this post. This young man was using a 300gr/XTP/MAG with 100 gr. powder.

http://www.huntingnet.com/forum/tm.aspx?m=3173622