I think that would be totally dependant on the brand of safe, what you were putting in it and how good you were at packing.

I friend and I were looking at a 30? gun safe at one of the local gunsmith/dealers, and he said he had the same safe for his own use out the back with a stupid number of rifles in it (I think he said about 100). he also said if he tried to fit another in he wouldn't be able to close the door.
I never saw it myself but have no reason not to believe him. he is not the type to talk up his achievements. the only time I heard him make a "claim" about anything (I thought it had to be bs as it was a BIG claim) he pulled out his phone and showed me the pictures.