I dunno....when ya run out'a room to put a new safe and all of 'em are full?
If its a collection as long as you have the room and funds, unlimited. I fall into the category of not being able to shoot what I have. I am hoping that will change when I join a club/range closer to me and the kids are a little bit older. I am a collector by nature, so while guns may not be a "good investment" they generally hold their value if not increase. I have collected baseball cards, die-cast cars, and sports figures as for comparison. They almost all were losing value hobbies/collections. To me it is a good investment in that I am going to collection something anyway, so it might as well be something that holds its value. I am by no means a prepper or thinking we are on the brink of SHTF but the collection would really turn into a good investment if anything were to happen.
When you go to sneak another gun into the safe when your wife isn't looking, only to realize there is no room in the safe. Now you need to sneak another safe into the house.
A collection is "too big" when the boat ride to the bottom of the Bay fails because the boat sank from the weight at the launch site.
This is self-calibrating; the more money you have, the bigger collection, and boat, you can afford.
Oh man... you are right! I need to buy some more guns quickly while I still can!!
Started to wonder when I saw a certain Mosin in the safe and couldn't remember where it came from.