Thread: Seating depth

I am using a Hornady OAL gauge, with the 223 modified case, and the barrel that clips on to the calipers and measures the ogive for my seating depth.
My question is will it make any difference to the measurement if the cases are slightly different sizes or do they have to be trimmed all to the exact size so the cases are seated at the same measurement?
Because I got the seating depth at a set size, then measured from the base of the case to the ogive after i seated every round and they are coming out different measurements, only slightly.
For example, I wanted to seat my bullets at 1828 and some would be anything between 1822-1836.
I am guessing this is the cases being slightly different sizes.

This is probably easy to understand, but I am having trouble so apologies if this is a stupid question