The number of actions made to fit the 3.1 lenght precisly is fairly small.
There are some vintage mausers that are the correct lenght,the mexican mauser is about right.
There are also plenty of 3.3 inch actions which are pretty close,the Ruger regular long action is not a bad choice, also many Mausers both commercial and military feature 3.3 inch magazines.
Another good approach would be one of the Husquavarna actions which although 30-06 length are very light and trim.
Yet another option that would work is`to take a model 70 action originally chambered for a WSM round,you can then have the bolt face and feed rails modified to feed the 7x57.The model 70 WSM action has a 3.1 inch magazine.
It takes bit of doing to come up with the correct size and length action for the 7x57,most of them have been built on actions that are 06 length thru the years.
Brit
