I lean on the ram, but don't pound.
I average about 4.1 gms/cubic inch using material with about a 10% water content, that has been run through a 10 mesh strainer.
Less for packed buds, but I use 4.1 as an anchor point to have a general idea of how much a column of a given size will hold.
If you calculate volume of a sanitary column, consider that the size given is OD, so you have to subtract the wall thickness first.
For instance, a 4" column with an .083 wall would have a internal capacity of 416 cubic inches, not the 452 cubic inches a 4" ID tube would have.