A really good place to start is to measure dimensions on another gun/guns that you have that you feel fit you and that you shoot well.

That can be a starting point.

I took my daughter to a fancy place to at least have her try the feel of a new gun for a birthday / graduation present.
I was surprised when I saw how just half an inch changed the way she held the gun.
I guess fitting is the way to go, but a couple of these guns I don’t want to touch even if they’re off.
The Parker’s I have vary from 14 to a long of almost 15 1/4. A hundred years ago someone had long arms.

Good advice,
Thank you all

Gun fitting can be a slippery slope that leads to no gun you own or find fitting you and you end up not being comfortable with anything unless it is custom stocked.

And some are very adaptable and can shoot a variety of guns.

I grew up in a time when most of us just shot whatever guns our fathers owned, or whatever was just laying around. Maybe, if you were lucky, your dad took you down to Western Auto or Coast to Coast and bought you a gun of your own. Heck; I’d be afraid to have a “fitting”; I’d probably find out I can’t shoot any gun I own :)!

I take a different gun after doves each day. When I only had a few guns after quail it was a Beretta AL2 with a one inch pad added. Now I shoot whatever gun I take and don't worry. Some I shoot better than others. A Beretta 686 does the best followed by an A5 Browning. Both have 1" pads added. But all of the American Doubles like a Trojan, SW, NID, Model 24, Nitro Special, etc. all resemble each other with about the same drop, LOP, etc. I just add a slip on pad. I had rather enjoy a different gun and not worry about altering each one. I was always told to put the gun in your hand and have your finger on the trigger, and the length should go to the crook of one's arm. Maybe an old wive's tale, but it seems to work as all standard stock over the counter guns need a pad for me at 6'2", and the pad also adds drop for me due to the extra buttplate to shoulder area.

Jack O'Connor once wrote that most people shoot a rifle with a LOP that is too long, and a shotgun with a LOP that is too short. Not that I think everything JO wrote is gospel, but after having been fitted many years ago, at the beginning of my stint in the NSCA that ended in Master class, I have to agree that for much of my life my shotguns were too short in the length of pull.

However, the right LOP for pre-mounted clays is usually a bit longer than the ideal for "low gun" or field shooting, especially so for colder weather.

As to how to find the best LOP for you . . . . . before I started any changes I would spend $30 for a copy of The Stockfitter's Bible by Rollin Oswald.

A few nuggets of wisdom from that chapter to whet your appetite:

"A stock of slightly greater length tends to reduce felt recoil slightly."

"The length of the trigger-hand arm has little to do with stock length."

"Changing the LOP one-half inch will change the distance between the nose and the thumb approximately two inches in the same direction. The ratio is very close to 1:4. It is mysterious and, to my knowledge, has never been explained satisfactorily, but is accurate."

"The most important (stock) dimension (is) drop at comb."

If you buy this book and regret the purchase I will buy it from you at purchase price and give it to someone.

Altered stocks
 

If altering factory stocks is a sin, I am in big trouble. Files, Bandsaws, table saws, and dremels are all tools that I have used to make shooters fit.

I resemble that.

You sound like Bob Brister, Tom, one of my most admired shotgunners and shotgunning authors.

I just shoot ‘em.

If fit didn't matter I would have bought those size 13 boots that were for sale here.
Unfortunately I wear size 10 1/2.
I might have made them fit with an extra pair of socks and newspaper in the toe but I wouldn't have been happy.
I have lots of shotguns that don't fit me properly and would never alter them. These are usually quality guns that I shoot and just shoot them knowing that it wont be the most accurate shotgun I will use that day.

I am not familiar with how crossover stocks are made but having observed a number of them I had assumed that the wood was bent, and bent along with metal adjustment. These stocks have more cast than all of the stocks I had bent to my specs.

When shooting dove or pigeons I am not so concerned with fit. After all when shooting Eurasian dove and pigeons if I miss a bird, 10 more will be flying in shortly. I can easily shoot a flat of shells on each trip.
Quail hunting on the other hand Im not sure I have shot up a flat of shells, over my dogs during the whole season.

When shooting quail over my dogs I want a gun that seems to just naturally comes up and shoots where I am looking, which is the bird scooting through the trees.
After all I hate to disappoint my dogs.