7mm STW on a standard long action.

Thinking about building one for some unknown reason.
Must be bored.

I realize the STW COL is 3.6".

What I understand all Savage long actions are the same. Same bolt I assume as the RUM length.
The bottom opening on mine is 3.59".

I read on this site in a previous post that you can use a modified centerfeed magazine and that will work.
What do you need to modify?

Also read that you need to modify the feed ramp which is not a big deal

The action is a staggerfeed control feed magnum action.

The stock will be a B+C duramaxx.

The ejection post is 3.8" long.

The mag is the same as the RUM, unfortunately those magazines are no longer available. Since the demand was so low, instead of a dedicated magazine, Savage actually cut 2 magazines and welded them back together to make it .220" longer. Once the staggered feed actions were discontinued, so were the calibers that used that magazine.