If you are shooting a factory gun a lot of what you're concerned with isn't going to make that much difference. Also a lot of what you're asking is why he told you to get a comp seater die. Yes, the seating depth will change on every bullet because of variance in ogive's. as a bench rest shooter your buddy is probably seating every bullet to within a .001" This isn't as hard as it may sound, with a comp seater seat all your bullets out a little, then go through and measure them with your bullet comp. seperate your cases by the depth of the bullet then start at the lower end by seating to the exact depth with all those cases, move onto the next which will probably only be another .001" difference so move your seater down .001" and do those, and so on. This will ensure the amount of jump or jam to or into the riffling is the exact same evey time. It takes a little more time but if you have done everything possible to eliminate loading errors you can focus soley on technique and not have to wonder what if I would have seated every bullet to the exact same depth. I once heard a guy who frequents this forum say at a match "A .001" here and a .001" there but with one little puff of wind it's all out the door" Keep working to make the most perfect loads you can then when you spend the money on that custom rifle you'll enjoy it htat much more!