I had a fitting with Chris Batha a couple of years ago and have a completed sheet with my stock measurements. The try gun Chris used was an AyA, which has a concave rib.

When you consider purchasing a SXS with a raised rib, such as the Winchester Model 21, do you need to adjust the measurements-say for drop@comb and heel to alter the at face measurement? If yes, does the amount of drop need to be increased?

And, if it does need to change, how do you calculate/guestimate the amount of change required?

Thank you.

I caution you about putting so much emphasis on "measurements" those were your measurements for THAT Gun.... Subject to change......with each subsequent gun....
Remember one very important principle....... Gun Fit is simply a matter of WHERE THE LOADS GO.... with any gun.... not .a set of carpenter measurements that will not likely carry over for multiple guns.....
Point of Impact connected to a particular Point of Aim......that is the essence of "Gun Fit"
Lots of guns and a LOT of Shooting behind my opinion.

Get fitted by three different guys and you'll end up with three different measurements.....

Did you shoot moving clays with the try gun?
Did you have a gun stocked to those measurements?

I wouldn’t worry much about the rib configuration. That’s a pretty small factor in the overall effort of shooting flying targets.

A gun fitting gets you close. You'll know roughly what sort of LOP, drop, and cast might work for you. But as mentioned above, each gun has characteristics that will affect how the final fit works.

Gun fit for side by sides and doubles are slightly different. Use what you got as a starting point and adjust from there by shooting at a pattern plate. Shooters who remount can almost lock into a higher stock than if they shot drop gun. I can shoot most guns that are within a decent range of being what I normally shoot. If stocked too high I need to carry the bird above the bead to compensate for a higher point of impact. That is what the pattern plate will show you, how close your point of impact is to your aim point. Once you know that adjustments to the stock or your shooting style are easy.

I’ve always heard that a gun fitting for a SxS vs an O/U is ‘slightly different’. So, what’s slightly different??

Winchester 21's don't have a "raised" rib, they have a level rib with a concave surface for the most part. Vent rib models like a Trap or Skeet do have raised, flat-topped ribs.
JR

Exactly what Mel said. Among other considerations: summer or winter? Heavy clothing or shirtsleeves? Weight of gun and where does it balance? Premounted or low gun? Instinctive shot or aimed? And on and on. Every gun will have different measurements and even those vary with the season. Good luck!

Concur with Joe and Mel that every gun is unique and varies from another. Having had a fitting does get you closer as a start point, but things will vary.

Reference the difference between side by sides vs over and unders. The barrel alignment gives a different recoil effect, in theory one pulls to the side some, while the other pulls up or down. Depending on cast and the particular gun the difference maybe greater or lesser.

One thing very few people figure in is the shape of the comb. The measurements seldom account for drop at face, and the comb profile is never quantified. A consistent gun mount must be developed before any fitting numbers are meaningful. As mentioned the mechanical influence of bore and choke being concentric, convergence of patterns on target. As Brister said art and science.

Thanks everyone.

not all my sxs are the same measurements, but pretty close at the face, which is usually about 3" back from the comb but could be different for you. The other point often missed but is critical is the shape of the butt. A sharp toe relative to your chest will throw the pattern high.

I've been fitted, and have the measurements from that session. They turned out to be extremely close to what I had already determined I needed, by shooting at a plate and making dimensional adjustments myself. That said, the only thing knowing my measurements are useful for is when looking at guns online, or ordering a gun. I can usually know, within a range, if a gun is unsuitable for me by examining the dims on it. But, nothing can take the place of shouldering the gun a few times. I can mount a gun and know immediately if I will be able to shoot it reasonably well. Years of shooting different guns is worth a lot.

"not all my sxs are the same measurements, but pretty close at the face, which is usually about 3" back from the comb but could be different for you."

I agree.

My preference is to only have sxs that shoot to the same POI (or very close to it) so that I don't need to make any adjustments when I go from one shotgun to another one. I'll shoot a new purchase at targets and at a pattern sheet at 16 yards. If I feel it's needed, I will have the stock bent.

Joe's point regarding "Premounted or low gun? Instinctive shot or aimed?" resonates with me. I've always been a low-gun shooter, but in the past I was much more of an aimer, and I preferred and shot best looking down a flat rib. I eventually weened myself off the barrel and I now prefer and shoot best with a higher comb well above the rib with either a SxS or an O/U.

It has to do with the difference in barrel flip. I need an O/U comb slightly higher. But most O/U shooting is not as low gun as side by side shooting so the higher comb seems easier to adjust to for my shooting style. Unless the rib is extra high it makes little difference to my shooting style but high ribs on side by sides just look hideous to my eye.

If a person has been fitted they need to consider it as a starting point not the answer to their shooting needs for every situation. It is a rough guide.

Does not barrel flip occur after the trigger is pulled? If a gun is properly fitted how does fitting a gun for barrel flip come into play before the shot? For the second shot?