I can use a vent rib.
I don't prefer them on a defensive gun because it still gives you less feedback on your alignment on the target than a good set of rifle or ghost ring sights.
In a circumstance where I'm firing a 36" cloud of shot at a 4 ounce bird 30 yards away, a little misalignment behind the gun due to a bad mount isn't going to make a lot of difference. In self defense we're not shooting at dude, we're shooting at small vital structures buried deep inside of dude. The nature of the shotgun being what it is, should we be a little bit off it's unlikely the other guy is going to nanny-nanny-boo-boo about it. Even so driving the fight stopping power in our hands exactly where it does the most good is a pretty good idea when we're looking to stop a threat.
A bead on a raised vented rib is vastly preferable to a pedestal bead or a bead-on-barrel. And the double bead isn't bad, either.
But no bead sight is going to be as good at doing what we're trying to do with a defensive shotgun as a proper set of sights.
A skilled hand with a shotgun can use a bead sight to a high level for sure. Because ultimately the thing on top of the gun doesn't shoot the gun. Skill on the actual controls of the gun pay off regardless of the sighting system.
But....and this is a big ol' hanging off both sides of the fatty scooter sized but...we don't even mount a defensive shotgun the same way that most people mount a bird gun. If I showed up to train with a sporting clays instructor with my teaching 870 and I adopted the stance and mount I want to use for defensive application he'd probably have a stroke. I'm mounting the gun inboard on my pec, not out toward my shoulder pocket if I can help it. I'm square to my target. These things are going to be suboptimal for following a fast moving aerial target across a wide section of sky and he will immediately start trying to "fix" that.
In self defense I'm swinging the gun a lot less of a distance at targets that are typically much closer and moving much more slowly. But I'm shooting a payload with real recoil. I'm shooting slugs or buckshot. I'm shooting a single projectile or ideally a pattern that is no bigger than the span of my hand, and I'm trying to land it centered on about a 3" circle on the other dude's anatomy.
Take a look at this picture:
I see this all the time. Most people will look at that and say it looks pretty close to right.
I'd ask that you look at it more closely and think about this: How much of him is behind the gun, and how much of him is
beside it? Do you really have optimal control if you're basically
standing beside the gun?
Look at how Kim Rhode mounts a shotgun:
Note that she's running that gun a lot more inboard than the proverbial "pocket"...but also note how stretched out she is on the gun. Her support hand is barely in front of the hinge of her break-action Beretta. Notice that her head isn't cocked to the side down on the gun, her head is erect.
How exactly has a 5'4" female sustained decades of shooting 12 gauge? How she mounts the gun is a clue. The equal and opposite reaction is loaded into the majority of her body weight, not just her shoulder joint. Her mount and stance are significantly different than most male clays shooters. If you look at pictures of Ben Husthwaite or George Digweed mounting a shotgun they tend to have a more bladed stance than Kim does. George tends to be closer to the "beside the gun" method, Ben tends to be about halfway between Kim and George in how much of him is behind the gun.
It's worth noting that both of those men have a lot more mass going for them than Kim does.
All of those names have spent countless hours mounting a shotgun, usually a shotgun carefully tailored to fit them so that it ensures the mount that is crucial to their success on the range.
I can't really say the same about your typical person who is reaching for a defensive shotgun. Hell,
I can't even say that about myself.
My mount is pretty good most of the time. When I'm standing on two feet. On the range. With my wits about me and a full understanding of what's going on. And I'm deciding to initiate the shooting process. I can set up in a real low ready (meaning the gun pointed at the ground YARDS in front of the target) and fire a hit in under 1/2 a second. Close to 1/3 of a second if I'm really on that day. That's pretty good.
But when it's early may, colder than usual, raining to beat the band and Pat Goodale is making you shoot slugs around an awkward barricade that you're having to twist your fat ass into a pretzel and be leaned way the hell over so you can fire a slug at 50...well...I'm not making that .33 mount to shot anymore. Once I ended up in an awkward position my mount ended up being lower than usual. It wasn't off by a lot, but enough that I would have missed entirely at that distance given how much of the target I could see downrange from this awkward position. I couldn't get my front sight into the rear notch and that was the clue that I needed to readjust.
Would a second bead on a vent rib have told me that? Maybe. What I can tell you is that with a red dot or a good set of ghost rings/rifle sights the feedback is
instantaneous and unmistakable. When you have a lot of other things to think about they provide a very clear and direct "YES" or "NO" signal. The benefit of that is sometimes difficult to see when you're standing on two feet in your most comfortable shooting position. But even the clients who are extremely skilled with a bead find themselves wanting something better the instant I make them shoot from the other shoulder. (Because the real world has corners that open to the left AND the right)
A double-beaded vent rib will certainly be helpful in that endeavor...but if I'm going to the extent of getting a front bead up higher and then installing a rear bead so I have some sort of reference at the rear to tell me if I'm actually looking down the rib straight...well...why not just go with rifle sights or a ghost ring at that point?
I'm not saying that the vent rib double bead is bad. You can certainly use it, especially if you actually train on it. But if I have the choice between that or something with real sights I'm going to pick real sights every time because they just do everything I'm looking to do
better. I can use rifle sights like a bead, but I can't use beads like rifle sights nearly as easily.
I think a lot of people misunderstand what I'm doing with rifle sights or ghost rings on a shotgun. They think I'm looking
at the sights, when in reality I'm usually looking
through them. If you get your mount right you're getting exactly what Jeff Cooper described as a "flash sight picture" and breaking the shot.If you get the mount wrong, you see the incorrect shape in the sights, fix it at speed, and then break the shot. If my mount is right and I'm shooting buckshot at close range I see the gross shape of the sights in an alignment that isn't perfect, but is "good enough".
"Good enough" defined as the front sight might be 2/3rds out of the rear notch, but at 13 yards if I just drive that front sight to armpit level I'm still going to get a solid hit. If it's low in the front sight notch if I just drive the sight to armpit level, I'm still going to get a good hit. If the sight is beside the notch or not visible in it, I've probably got my push/pull out of sequence. Etc. I can see this in hundredths of a second, correct it in tenths.
My focus is on the target unless I'm shooting a slug for precision at distance.
This is exactly what somebody who is using a vent ribbed bead would be doing...only my rifle sights provide me a lot more reliable and instantly comprehensible feedback on alignment when I need them to than their bead does. Especially if I make them grab and mount the gun in uncomfortable positions or awkward circumstances.
...circumstances that are much closer to resembling what you might be doing if you are responding to an armed home invasion than setting up on a sporting clays range.
So it's not that the vented rib double bead can't be used to a high level in defensive use, because it can. It's not even that I can't use such an arrangement to get acceptable results, because I can. It's that system is inherently limited when it comes to doing lower percentage but still realistic things with the gun while providing no real benefit in the fast and close stuff over irons.
Vented ribs look sexy as hell, without question. But I just don't want to be stuck fighting with one if I can help it.