I settled on a LOP for my Sabatti 450 NE. It originally came with an LOP of 15.125" When I got rid of the rubber butt pad and installed a real recoil pad I kept the LOP at 15.125," which was too long.

I started by taking off the existing pad and shouldering the rifle. With a 14.125" LOP it was comfortable to the front trigger. I have various butt plates laying around so I experimented with different thickness. The one that felt the best yeilded 14.375" to the front trigger and 13.375" to the rear, so I cut the stock and reinstalled the pad. I shot the rifle yesterday and it was comfortable. Turns out the top joint on my trigger finger lines up with the front trigger.

BTW, I still like my single trigger O/U shotgun at 14" and my scoped bolt rifles at 13.5."

There are a lot of interesting opinions here. I think the simplest answer is often the most correct, so here is my 2 cents.

Go to the Dallas Safari Club or SCI convention next year. Go to the Verney-Carron booth (Ken Buch) and ask Jerome to measure you for a double rifle. He will do this free of charge. He will write down your measurements on a business card and hand it to you. You now have your correct double rifle measurements.
QED

Rip
. I look fore word to seeing you and your wallet again next yr at DSC