several days ago I bought the "Big Boy" and several other items from Arturo in Diamond City. Piper was my companion at the time. I was over weight so I struggled over to Piper's house and stored "Big Boy" and a few other items in a locker...came back yesterday and all the items are missing...is there any (real) safe place to store items and will the "Big Boy" come back to Arturo's inventory again?

The big boy shouldn't go back to Arturo's inventory, you may have lost it. If you're on PC could use console commands to get one, otherwise you might be sol. Containers in Beth games are generally always either 'safe' or 'unsafe'. Safe containers remember what you put there/took out of there indefinitely. Unsafe containers refresh their inventory after a set time. The container you put it in was likely the latter, which is why your stuff is missing now. Until the GECK is released, there's no way to tell for sure which is which until something like this happens, but so far, it seems that any container you make yourself at a settlement is safe (at least in my experience).

Workshops in your settlements are safe, as are all crafted containers.

Not sure about other containers in your settlements, I've put an item in one and it's been there for more than a month so.. I guess they are safe too (don't quote me on that though!).

Anything outside these are a guess, you better not gamble with uniques or loot you like

Yeah you probably lost Big Boy, sorry!

yeah...on PS4...they should refresh the vendors stock for us console users until GECK is released...thanks