I tried to move a 600 lb Liberty safe with a heavy duty Appliance dolly and 3 strong young men. We didn't get very far. LOL!

It's more for the room than anything. I am hesitating buying a decent optic for my AR because my current cabinet thing is so tight front to back that I don't think it will fit in there with an optic and I don't want to scratch and ding up an expensive optic in my shitty cabinet. I could get a similar shitty cabinet but from what I can tell it's still going to be an issue in that depth department. When Is tarted looking at my options and weighing size, weight, and cost I found this one which is my best middle ground.

Um, trial and error?

We asked an architect about reinforcing our floor before we brought our safe home. It was a very helpful conversation and they were able to tell us exactly what we should do based on the flooring and size/weight of the safe.

mislabeled, yep, our contractor told us how to secure it to the 2x6 floor joyces and put it in a corner.
A safe not secured to a floor is a potential stolen safe.

That said, I know a guy that had his in the corner, secure to 2x6 floor joyces, and the theives just punch a hole through the outside, drywall, wrapped a chain aroudn the safe, and literally ripped it out the side of the home with a big truck.

Yeah, they're fairly tight. I was using Stack-On 8-gun cabinets, and on some of them I removed the little "gun divider" that goes on the back wall, to get more space. I can tell you with certainty that they'll hold way more than 8 guns, though if you're really sensitive about scratches and dings . . . well . . . yeah, it can happen.

We didn't discuss securing it from theft (though that has been done). We only asked for advice on providing additional support from below to maintain the right load level.

There is no way I can bolt it to the floor here or the wall. I might I can hang pictures but putting in a foot long lag bolt isn't going to fly. The benefit of this safe to me is it can be bolted at a later date if I move.

The thread title referred to determining how heavy your safe should be for the floor you have. An architect or a structural engineer would be the right place to look for the answer. If you choose to secure that safe once it's installed, that's a different conversation.

I wouldn't worry too much about a 400# safe or even one heavier. I had a king sized water bed in a 3rd floor apartment with no issues. That sucker weighed close to 3,000 lbs.

Most floors are engineered for 150# per square foot and some even more.

Oh yeah, I also had a gun safe in the apartment. The nice thing about the water bed is that I could drain and fill using a hose and a faucet adapter. The rest didn't weigh that much. No way I could "drain the safe" in order to lighten it.

You should buy a bunch of gun socks and just shove all your firearms into the safe. Pack them in tight.

yeah, we strayed off topic, Jesse.

Lots of good advice. Best advice is to put the safe against an exterior wall. Putting it, along with guns + ammo + all the other shit we collect in the middle of a span creates un-needed deflection and you can get a "bounce" when you walk. That loaded bounce is the last thing you want when you are 4-stories up and there is a ground shake happening, unless you want to donate your belongings to the neighbor below you.

No, it's a different conversation as in residential architects don't usually have much experience securing things like safes. They do a lot of earthquake bracing for appliances and other typical home stuff, but if you ask one about bolting your safe down they probably won't be able to offer you much advice. Floor loading, yes. Securing from theft, not so much.

Once you're ready to install it more permanently, I would imagine the guys at NW Safe or somewhere similar could share a lot of good experience in that area, though.

All good advice here, if you're concerned then close to an exterior wall or load bearing wall (from below) as possible. One thing to think about is the structure type of your apartment complex, likely not all wood framed being 7 stories, more likely 4 floors of wood framing over 3 of concrete (slab & columns)....or even possibly 4 of concrete, do you know if the actual floor you're living on is concrete or wood (sub-floor under your carpet)? If concrete you're in a little better shape & there won't be any load bearing walls in the floor below, just shear walls & columns, & you can feel comfortable placing your new 400# safe where it suites you best

Another option not mentioned is to buy two smaller safes, and secure them well. You could even have one well-hidden & well-disguised with higher end stuff, and another with ammo and cheaper items.

Still secure them well, but if your next move isn't into a house, this might be a good option.