Jacko - book I have on wildcats shows a fellow with a .348 Ackley Improved Winchester Model 71. In this rifle, he was shooting 300gr. gas-check bullets that had to be seated well below the case neck, which is relatively short in that chambering.

His lever actioned rifle printed group after group of around an inch and a bit better than inch at 100 yards off bags. He used crimp-on gas checks - seating below the case neck does not bother me any more.

If using very fast powders like Red dot or other shogun powder, there may be an opportunity to gas cut. With rifle powders, which you are using, the bullet will be well into the throat before any powder gasses get at it's base.

With rifle powders, if there is gas cutting of the bullet and it's base, it is due to a too-small bullet for the groove diameter or too low pressure for the alloy to obturate to seal the throat, not because the bullet was seated below the neck/shoulder junction.