Why do some half gallon ice cream containers appear smaller than others?
Welcome to the SDMB.
Perhaps the shapes of the containers differ giving the illusion or appearance of one being smaller than another ?
ice-cream eating scientists will be here soon…
Could it be that some ice cream is packed harder than others? For instance you can get hand packed ice cream at Baskin-Robbins. Just a guess. 
I’m going to support the shapes-provide-optical-illusion hypothesis. A rectangular package placed with a long side facing the aisle is liable to appear larger, to a casual glance, than a cylindrical container. (There are also varieties of boxes where the lid is a separate piece of cardboard and it “enlarges” the appearance of the container.)
HOWEVER, I will also point out that several dairies have begun selling ice cream in 56 oz containers that are actually 12.5% smaller than a half gallon, so that there is no optical illusion–they are truly smaller. (Read the actual labels on the next carton that appears smaller–perhaps it is smaller.)
ok, so let’s enhance the shapes theory and add to it the volume theory. kinda like different sized coke/pepsi bottles. so a shorter container need not be smaller, as long as it holds more volume.
and i’ll second kniz’s packing theory. and tomndebb’s lid theory.
Thanks for the great response…gave me some possible solutions to my quandary.
The packing theory makes no sense; ice cream is sold by volume, not by weight; packing “harder” does not make a half-gallon any bigger or smaller.