Mother of god AJ...that's a beehive round, not a shotgun!
Hmm...how many pellets? 45-50?
If you are going to go the NFA / DD route, why not make 1.5 gauge? (37mm grenade)
That launcher you ordered?
Yep.
Birdman... the 40's generally have shotshell loads that are just the equivalent of a 12ga in the center with wasted space around them. Also, the larger diameter bores seem to be a lot less forgiving when it comes to internal yield pressure/yield strength without also being crazy thick. The CZ 26.5mm launcher I'm getting has an extremely thick barrel because while it's sold as a "flare launcher" (Dr. Evil finger-quotations made in the air...), it was actually used to fire very hot barricade/wall penetrating CS shells at up to several hundred meters.
The fact that 26.5 just also happens to be a common European flare standard is serendipity.
I haven't seen too many people making shotshell loads for the 37 or 40 either. (I believe most people bore 37's out to 40 when getting them registered as DD's as well) Also, the 26.5mm has longer skinnier drag or fin-stabilized projectile designs available for it with better SD's, which seem to be more ideal for actually getting some long-range accuracy out of the thing.
The one area I do agree the 40mm DD's shine is the multi-barrel .22LR beehive adapters. I think some are as many as 18 shots now. Nobody will touch the idea of making 37's or 26.5's like that with a ten foot pole, lest they be the jerk that loses the the option to be owned and sold as non-DD's for the rest of us.