There often will be a difference, in fact I'm more surprised when I find two brands which are really close in results. Until you spend the time doing the testing, you are just guessing. Be aware, there are folks who would tell you this primer is the same as that primer, yet they can't lay out the targets and information to back up their claim.
Plus, always remember, things will work differently in your firearm.
A lack of planning on your part does not necessarily constitute an emergency on my part.