I guess I'm probably in the minority here...I seat my rounds to fit the magazine. If a bullet doesn't shoot so seated, I look for another. I don't have any interest in using my 300 as a single shot except maybe for some experimentation/plinking.
Of course, its mission is probably a little different than some others' here. It's a light hunting rifle. As it sits now it's just a hair over 9 lbs and with the new barrel should still be a hair under 10 lbs with scope mounted--which is pretty light for a 300 RUM. It's a "do everything" rifle. I want to be able to reach out as far as possible, but I still spend a bunch of time sneaking through the brush where I've killed bucks at 15 yds with it. I haven't needed a follow-up shot in 15 years, but I want to have them available if needed. And the last thing in the world I want to have to do after jumping off a horse and yanking it out of the scabbard...is loading the **** thing!
Of course it's a compromise, but I really don't think I've left much accuracy potential on the table from such a light rifle with such a skinny factory barrel. It has done as well as possibly could be expected. I believe there's a hell of a lot more to gain from a quality barrel than there is from playing seating depth tricks that will only be a pain in my *** in the field.
For a 12lb, 15lb, or heavier rifle that would see a more specific "long range only" mission, I wouldn't have a problem with it. Maybe one day I'll build one of those. But even if I did, I think I'd still be spending much of my time carrying this one. For the ranges I'm likely to shoot, I don't see this compromise as being a deal-breaker accuracy-wise. Maybe not optimum, but I've got bigger fish to fry.