I want to build a 7wsm on a long action and was looking at savages web site and saw that the 300win and 7rm had different part #'s. I was thinking the bottom metal is different?? Which one would i want?
Well here are my thoughts and take it for what it's worth. The 7mm WSM is designed originally as a short action caliber. However, due to the many bullets and lengths that it can shoot effectively... a short action may cause issues when trying to eject a loaded case with a 160grn bullet or heavier due to length. Generally having to release the bolt to eject a non-fired round. Therefore a long action sometimes is the preferred package when using VLD's. But if you leave the gun loaded during the course of the hunt, then you won't have to eject until the end of the hunt or the day, what ever the case may be resulting in pulling the bolt out not that big of an issue.
But you can use a short action in many cases especially if you are going to shoot lighter bullets. In some instances if you load a bullet to mag length, through using different powders and length combination's providing usability of the provided magazine. A good example is my 300WSM. It is built on a Savage short action with DBM. My 208grn Hornady A-max's are currently seated .005" off the lands. This keeps the tips of the bullets off of the inside of the magazine and providing .6 to .7 MOA at 245 yards. I am waiting to go longer to see how it does, but at 100, 200, and 245 yards, it is consistently in the .7 MOA or less. I usually get one flier which is more than likely me rushing a shot or not sitting on the rifle the same.
So to answer your question, any of the actions will work. Personally I would build off the target action in the Dual port (right bolt, left load, right eject; good for rapid fire with no magazine) or the right bolt and left port model. It is nice to work the bolt with the right hand and catch the casing with the left. If you want a repeater then the varmint with the DBM would be my option. If you plan on using 168, 180, VLD's (Berger, or JLK) then the long action might be the better option for loading into the lands and still maintain a repeater, or if you are going to shoot single shot, than refer to the above. Think application in you decision, Prairie Dog rifle/Ground Hog/predator, silhouette, tactical comps (multiple quick shots: DBM, or internal box mag), or Deer/Elk, paper target (slow rate of fire: single shot).
Hope this helps,
Tank