I have to tap the barrel which is trickier because of the pressure stuff. I’m not sure if they can tap the vent rail affectively or not.
First off, lets be clear on terms, a rail is for mounting something, a rib is a solid surface to sight along. A solid rib means just that and is in full contact with the barrel along its entire length. A Ventilated rib means the rib stands a bit above the barrel on several "legs" and only those are in contact with the barrel, the rest of the length is open air space, which promotes cooling, and also looks good.
Generally speaking shotgun barrels are THIN compared to rifles and pistols. VERY THIN. Enough to safely handle shotgun pressures but nothing close to the thick barrel of a rifle or pistol.
And, that's your big problem with tapping the barrel. Its not so much a pressure issue (though that does need to be taken into consideration) but its because the metal of the barrel is so thin you can't drill and tap deeply enough for the screw threads to get a adequate grip, without drilling through the barrel, and that's a bad thing.
you might be able to mount a rail, but the "hold" of the screws will be very iffy, and anything you put on that rail will make that worse during recoil, very likely stripping our the screws. Any kind of scope or dot sight will "torque" during recoil putting strain on its mount and while on rifles and pistols its not an issue because of the location of the mount (receiver, generally or an a barrel thick enough hold the screws well) on a thin shotgun barrel its simply something very unlikely to work well.
Sighting ribs (that support nothing) are not screwed to the barrels, they are welded/brazed (silver soldered usually) on, not fastened on with screws. There's a reason for that.
The only place you find threads into a shotgun barrel is the bead sight (small and light) and internal choke tubes, where the threads are long (several times longer than the barrel is thick) and all the pressure and recoil forces are not acting to twist a scope or dot sight off its mount.
So, mounting a rib or even a rail on a shotgun barrel with screws alone possible but not the best method.
Putting anything with any weight on that rail, BAD IDEA.
but the idea is a still shot Way out there with accuracy mimicking 22 mag.
Sorry, but this is not happening. Energy possibly can match but accuracy simply will not. And, its not a matter of shot charge
weight.
You are comparing apples and watermelons or something even further dissimilar. Look at what you are shooting from your shotgun. It's a mass of round pellets, not an aerodynamically shaped bullet and NOT spun by rifling to keep it flying straight to target.
next point is that useful range is determined not just by the power of the load but also by the shot size of the pellets and the pattern density.
Small shot loses speed faster. Bigger, heavier shot go farther. BUT, all of them spread out as they go down range.
The point of a pattern is so that there are enough pellets close enough together at a given distance to strike the vitals of the game and humanely dispatch it. The greater the range the fewer pellets are likely to be "in the right place" and the greater the likelihood of a wounded animal or a complete miss.
You WILL NOT get rifle accuracy from a smoothbore shotgun, no matter what choke it uses. Full and extra full chokes keep the pattern density together further, extending useable range not actual range, and at the cost of covering a smaller area of space at every range. Not a huge deal for bunnies, but important when wingshooting.
A heavier shot charge does not extend the range, what it does is put more shot in the air. And there's issues with that, as well.
Consider this, the bore size is a fixed constant. SO increasing the shot charge weight means that the shot column must get LONGER. Since your target is in a single plane compared to the shot string that means most of the shot arrives AFTER the leading pellets have struck and done their job.
Doing very little useful and possibly being overly destructive of game meat.
Assuming you're pretty new to all this, your questions are reasonable, but some of your assumptions are flawed.
Hope this helps and gives you some new things to consider.
