It does not matter the size. If you feel like you need 3" slugs by all means use them. I have a 500 and use 2 3/4" slugs and it still kicks like a mule. I have a rifled barrel and can not seem to find a slug that shoots consistant past 50 yards. If your state allows 5 slugs for deer season then you will need a plug if can hold 6. Brother do not be caught by DNR for having space for an extra shell. Overall what you really need to do is buy a box or 2 of different brands and sizes and shoot them until you find what works.