I have both the smooth and full from Swinglock. The one from Hankins isn't adjustable. The Swinglock version can be adjusted in .0005 increments. The adjustability is needed for when you run across that lot of bullets that are a little larger or smaller. Or when the fouling doesn't allow for ease of loading with full form. I haven't tried any of this with BP or subs yet. Just smokeless. So I am still at the beginning of the learning curve. What I do see is a very high increase in accuracy and consistency but it did take a little practice in getting the adjustments just right for my particular barrel. Oh and yes the Nosler 300bt is a .458 which you will need if you are going to use full form. The smooth you can use .452 or size down a .458. When using a smooth sized, I would recommend a card or a bullet base which you figured out already. Full form doesn't need anything.