If you start taking exact measurements on originals you will find they vary, like Ken said, but what matters is what flows for your gun and each gun is different. And of course, some originals look better than others. I think they generally look good if the lock is level or tipped back just a tad, but you don't want it tipping forward as this will tend to interrupt the flow of the lines.
One thing I do is lay the stock out on a long sheet of paper, with the barrel in, and do a light, but very close pencil tracing of the profile from the butt to forward of the entry thimble. Measure the breechplug and mark the location of the face of it on your drawing. Photocopy your lock and triggers, and make true size cutout patterns. Mark the location of the sear on the outside of your lock picture so you can then lay the triggers in the right position, and the guard etc. Lay them out on your pattern in the positions they need to be - this will show you how much wood you have to play with. You can move the tail of the lock up or down a bit to see how it looks. Then go in and redraw your lines - the wrist, toe, lock panels etc inside of the original lines until you get the look you want.
The exact center of the wrist won't be determined, even on a precarve, until you get the lock and triggers in - guns are essentially built from this point forward and back. (I'm assuming you have the tang inlet but you also can still do some filing on the top of the wrist for final shaping.) So if you haven't yet, I would not do any more shaping in this area - leave your lock panel areas wide and your toeline where it is - until you get the lock and triggers in. Hold off on inletting the guard. Once these are in and set, then go back and tweek the shaping to where you like it - i.e. you will be taking a little off the top and bottom of the wrist, and shape the height, thickness and shape of the lock panels, to give the flow you want. Trigger plates sometimes need to be bent, trimmed or filed down in thickness, and there is also usually more wood to remove than it seems at first, on your first gun. Then inlet your guard after this area is about at its final profile.
One other trick Mel Hankla just told me recently - I know many of the Gillespie rifles used one lockbolt but if you happen to be using two, when you start inletting the lock, you can drill the front lockbolt first, before you inlet the plate. Then use the front screw as a pivot and move the tail up and down till it gets to the position you want, then mark it and inlet the plate.
This also allows you to make your sideplate shape flow with the lock as it sits - rather than try to force fit a pre-cut sideplate to your lock/bolt placement - which causes some contemporary guns you see to have sideplates that look like they are tipped more than they should be.
Good luck
Guy
