Seating bullets too deep in pistol loads can increase pressure greatly. With magnum loads in large cases it can compress a powder that may not be good to compress.
Since you are loading for a lever gun. You will not run into a problem. Bullets should have a crimping groove. You will need to crimp to prevent the bullet from being pushed in too far creating the higher pressure. Also with the slower powders for the hot loads a good crimp is needed to hold onto the bullet that extra split second as the powder fully ignites. If not loads can get erratic.
I am sure someone can explain it way better than I can. I am just a guy on the internet. (In real life I am a dumb janitor.)
No matter how many times you do it and nothing happens it only takes something going wrong one time to kill you.