Floor loading limits are there to force a very high degree of safety, and they are intended to limit long-term load induced sagging of the structure. They are not intended to represent a safe loading limit on a momentary basis. If that were true, a 250 lb man, standing on one leg probably exerts somewhere around 65 lbs/sqft. If the live load was the basis of the specification, it would be many times that number. A 1000lb safe with a 30x25 footprint only exerts 28 lbs/sqft, unless it's elevated with pucks or some other means to concentrate the loads. Installing near a wall adds a degree of forgiveness to this calculation, as it's is near supporting walls.
You should not be concerned with any "normal" gunsafe floor loading in a second story room, unless the home is very old is structurally compromised...