Cheap gun safes, especially Chinese made safes that are sold in big box stores, almost always have weak shelves. The shelves are made of inferior particle board which is thinner than it should be, so the selves hold very little weight before they sag or break. I have seen brand new Chinese made safes that sag just from their own weight. Naturally, the wider the safe is this worse the problem becomes.
In my opinion it should not be necessary to fix a problem like that with a new safe, or avoid using the shelf for fear of it breaking, but there is an easy fix. The clips that the shelves rest on are usually 1/2” or 5/8” wide. At your local home improvement store buy some metal u-channel or square tubing that is big enough to go over the clips. Cut the material to the correct length and slip it over the clips on both sides of the safe. Your shelves will then lay flat and hold much more weight than before.
Fort Knox being a quality oriented company uses better, thicker shelving material. And on 51” or 61” wide safes they install tubing for support at the factory. As I always tell people, don’t save a few dollars by buying Chines made junk – buy an American made gun safe from one of the few trustworthy manufacturers.