Take a photo of the original work and blow it up until the butt plate height of the photo matches the height of the original then measure the width of the P.B. lid. If you have a good 90 angle photo of the original work you can make a pattern of the original patchbox this same way. I have found that after you have the pattern it is best to reduce it by about 5% before using it as a pattern. We trace around a pattern and then saw and file down to the line thus your resultant P.B. has grown somewhat larger than the original.
Ron
That is exactly the way to do it, but one complication is that if you change any dimensions, esp. the pull length (which is common), you may need to adjust the original dimensions to your "copy" to maintain the proportion of PB to buttstock. I've seen some cases where the PB was probably exactly copied from an original, but the stock was dimensioned noticeably differently, making the PB look too short, too long, too squat, too thin, etc. when compared to the model.
If you take the buttstock photo of the original and scale it to your rifle (which you might have already done to cut the profile out of the blank), then take the patchbox pattern from that as stated it should work fine.
