I'm going to be shooting a double rifle today at the range and got a look at the rifle yesterday. I don't know who the imaginary person the stock was fitted for (it's a prototype rifle, the first made) might be but I find the stock to be very awkward: not enough drop, no cast off, too thin in the grip, etc, etc. When shouldered I don't even come close to lining up on the sights.

What are the "average" stock dimensions for a double rifle? I know there probably isn't an "average", but when a double rifle maker makes a factory gun, what would the dimensions be?

Stock dimensions vary from one person to the next. I notice small differences most on lightweight shotguns but, the same applies to heavy double rifles.

These two are pretty large (from my perspective )
1 1/2" drop at comb, 2 1/2" drop at heel and 15 3/4" length of pull (centre).
Drop at Comb is 1 & 1/8". Drop at the heel is 2". LOP is 15.5".

I'm more in the 1 1/4", 2", and 14.5" in range in general and need some cast off. I'm obviously smaller in stature then the two dimension above.