Re: RCBS competition dies
Yes it will work for the 300 WM with the standard shell holder due to the extra length of the 300 case. the seating collet and top punch are already 30 cal so no problem there. Or you can buy an extended shell holder for the 300 WM from RCBS if you like.
You can also buy additional caliber collets, seating stems and shell holders for other calibers. It's much cheaper than buying micrometer seating dies for each caliber. I use one seating die for all my calibers by switching parts, which takes only a minute. I even have custom made collets and seating stems for my 338 Lapua Mag furnished by RCBS. Just check with RCBS for ordering info. Easy Peezie.