Three things will detract value from a double rifle:
- Over Under Configuration
- Rimless Cartridge Chambering
- Single Trigger
You are considering a double with two of the three negative features. That’s okay if you are aware of how these devalue the rifle.
Over under rifles have to be opened at a greater angle (much further) that do side by side configurations. This could hinder fast reloads.
Rimless cartridges require a spring-loaded pawl machined into extractor. That’s one more thing that could fail. I’ve had Chapuis and Merkel doubles with single pawls in each extractor. They functioned as designed. I also own a Heym 88 in 458 Winchester made in 1986. It has dual pawls in each extractor. I’ve owned the rifle for three of it’s 39 years of life and have fired it 500 times. I think it’s been fired at least 500 times before I became it’s caretaker. Let’s call it 1000 rounds and it’s pawls still function as designed.
Rimless cartridges such as the 375 H&H also operate at higher pressures than rimless counterparts. I would NOT own any double in a rimless chambering that does not have a Greener cross bolt or its equivalent.
The Kresten cross bolt appears to be a similar to a Greener for over under guns. I once owned a 375 H&H over under that would open slightly whenever I fired the top barrel. I really liked that rifle but had to pay JJ Perodeau to add more lockup. JJ also informed me that my 2500 fps 300 gr TSX loads were a little warm for this rifle. Once JJ repaired it, I passed it on to a new caretaker who would appreciate it.
Single triggers turn double, separate rifles into one rifle with a single point of failure. Nuff said?
Now, in theory the recoil forces on the rifle and shooter, SxS rifles’s barrels move outward from the centerline of the gun. This outward movement is of course along with the upward movement. Remember guns start their recoil as soon as the bullet starts to move from the brass into the rifling. The SxS rifle must be regulated for specific loads so that the point of impact of bullets fired from right and left barrels are the same at specific range from the rifle. That may be 50, 70, 100 or more meters. Most are regulated to have the same POI at less than 100 meters. To me, ideally the bullets would travel parrel to each other with POI the distance of the center of the barrels from 0 to infinity. That would however be nearly impossible with variables such as humans and other things...
A O/U rifle’s barrels each recoil upwards rather than side to side. In theory, the deviation of POI between bullets fired from top and bottom barrels should be much less than a SxS. If this theory is correct, the O/U rifle(s) should regulate to a wider range of load variations.
If you like the O/U rifle, and it is priced below, maybe significantly below a SxS rifle of comparable quality, grade, workmanship and so on, buy it and enjoy it! Just remember that if you decide to sell it someday, only a small portion of those desiring a double rifle will consider a O/U.
PS: There is an AH sub-forum specifically for double rifles...
Photos below are of a Greener and Kersten cross bolts on SxS and O/U guns