All right Jim. Here's some thoughts.
Cartridges, as a general rule, seem to like 75 to 80 percent loading density. That burns nicely and consistently.
Cowboy shooters, in an effort to 1) get as low a recoil as possible, and 2) to get as many loads for the least amount as possible, use both extremely light powder charges and extremely light bullets.
This, as you might imagine, leaves massive amounts of "empty" in the cartridge case. When you add in the fact that many of the cowboy shooters are using old cartridges, that were designed in black powder days, and therefore have large powder capacities, this just seems to be begging for a disaster.
With a normal amount of powder in the case, the primer flame sets the rear of the powder on fire and it burns progressively. With a itty bitty amount of powder in the case, it's all laying on the bottom of the case, the primer-flame flashes over the top of it, and sets the whole charge off at once.
The other problem is that, with a very small charge of powder in a very large case, it is possible to double-charge, and even triple-charge the case. This results in the gun turning into a handgrenade. Hard on the fingers.
For a long time, people that shot very light loads were in the habit of pointing the gun up in the air, before firng. This let gravity pull the powder to the rear of the case, and covered the flash hole. Then when you came down level powder was still up over the flash hole and you did not get the flashover. No one seems to know about doing that any more.
IMR developred Trail Boss, to be a BULKY powder. To take up LOTS OF SPACE in the older black-powder cartridges. You can load a light, low-pressure load, but still have a large amount of powder in the case. You don't have the flashover or the impressive detonation of your gun.
Most of my experience has been with pistol. I shoot it MUCH MORE than I do rifle. When I do do rifle, I use "normal" loads. Although I do shoot light cast-bullet loads in both 308 and 30/30, using eleven and ten grains of Unique, respectively. And, before I fire one of them, I point the rifle muzzle to the sky, to get the powder to the back of the case.