Im so new to double rifles that I hesitate to respond; BUT Im not new to wanting one.
The rest of your post below confirms the above statement!
First I think the "double shotguns don't regulate" is a bit over stated, or at least accuracy is too much of an issue.
Double barreled shotguns only overlap 30 inch patterns, and for every double barreled shotgun that will place slugs from both barrels inside a 12 inch bull at 40 yds there will be 100 that will not hit within 2 feet with both barrels' shots!
"SHOTGUNS DO NOT REGULATE!"
I have a 410 Baikal double that was good enuf to make adding a cheap set of express sights and even a scope mount. Second at the very least a scope can be set for the first barrel.
Was good enough? What is good enough? Setting a scope or iron sights for one barrel is not REGULATING! You may as well simply use a single barrel shot gun that patterns slugs with that barrel. A double rifle is supposed to REGULATE BOTH BARRELS to shoot side by side at the same elevation no matter the range!
A double shotgun is good training for learning the use of two triggers, and instinctive shooting with shot shells, but double barreled shotguns do NOT regulate It you take any shotgun and place a clean target at 30 yds with an aiming point in the middle the target and fire with a rest holding on the center of that target, then measure the pattern and find the center of that pattern! Do this on separate targets with each barrel, and then compare the two centers
of each barrel in relation the aiming point and 90 % of the time the centers of each barrels pattern will be at a drastically different point on the target than the other barrel! Now do the same with three slugs from each barrel the same way and fine the real center of each barrel's group on it's on target in relation the aiming point on each target! I think this will open some eyes!
The only way to regulate the barrels to shoot side by side at the same elevation at a given range is to place wedges between the barrels and move them back and fourth till they shoot properly!
If you take the barrel set off a real double rifle and place the lugs in a padded vice, with the sights on the center of a bull at the distance engraved on the back sight, then take two empty cartridge cases with no bullet or primer, and look through the primer holes like a peep sight. What you bill see is the
RIGHT barrel will be looking at a point that is
LEFT and low of the aiming point! The
LEFT barrel will be looking at a point that is
LOW and on the
RIGHT of the aiming point.
These barrels have to be this way so that when the rifle is fired with the sight on the aiming point the barrel being fired moves
UP and
away from the other barrel while the bullet is traveling down the bore so that when the bullet exits the muzzle it will be pointing at a point that is just on it's own side of the point where the sights pointing when the trigger was pulled. This is the way the barrels have to be to account for recoil
muzzle flip, and
Barrel time .
Shotguns do not need to be that precise and so only need to have their centers close enough to make the 30-inch patterns over lay each other well enough to hit a bird that is someplace within than 30-inch pattern at 30 yards. I don't think anyone would want to go into the weeds with a wounded leopard, or lion with bullets that shot not closer together than 15 inches apart! Do you?