Whichever way fits the most rifles in the safe.         andyz

Muzzle up without excess oil to run down and spoil the wood! 

Froggie

muzzle down will keep over-oiled rifles from having excess oil soak into the rear of the stock mortise.  this prevents discoloring and oxidizing the wood as well as helping the inletting preserve its integrity.  oil damaged wood is ugly and it can cause problems with heavy recoiling and poorly inletted guns.  store muzzle down or simply use common sense and avoid over oiling ???  your choice.   

personally I store mine flat in cases or horizontally on a rack. But if I had to store a gun vertically for any length of time I might consider muzzle down over a short nylon bore fitted plug mounted on a hard base with a felt pad.  this would keep the gun from slipping and protect the muzzle.  I'd consider it for heavy barrelled target guns because I suspect they'd be a little safer that way rather than have the heavy barrel weight, gravity, and angles working against the action bedding and the wrist of the stock

My answer would depend on where your safe is located? Mine are in my celler loading room. With a de-humidifier running and the humidity at 45% I still have to keep after the blued metal and even had some kind of mould/fungus growing on the oil finished stock of a custom model 70. The safe had foam on the bottom. I now have plastic blocks under the but plates so that air can circulate better. 
So, if there is the slightest dampness I would go muzzle up with anything but foam or carpet under the butt. If you have Arizona type dryness then muzzle down is probably good.