When you start talking about using GPS to measure true ground measurements you need to take into account your your elevation (ground to grid difference). Depending on the mean elevation of your range this may or may not be an issue. All GPS measurements are dependent on how your GPS is setup...
For rounds being shot out of the same rifle, neck only until you need to go FL. For hunting I always check for chamber fit and set aside the tight ones.
The action on the model 88 is a "turning bolt" type action. They shoot as well a any bolt action rifle. I have shot several and all were tack drivers with the correct load. The twist rate can be measured. Pretty sure they were 1:10.