Questions ,questions , If this keeps up I will surpass my answers.
How safe is it to shoot old ammo,probably 1920 ish. Made by Remington Arms Company Inc.Bottom flap says manufacturing experience of over half a century..In the green box ; Kleenbore. Non corrosive.Thanx.

By the description of the box it's newer than 1920-ish, by a decade or so. Would I shoot it? If I were desperate, maybe. I've shot lots of WWI and Spanish-American War ammo to good effect, but that was many years ago when the stuff was only 60 years old or so - don't think I would do it today. If desperation truly sets in, I would pull the bullets, dump the powder and primers, anneal the necks (because that's where they're most likely to fail if shot as-is), and replace primers/powder with new stuff and re-seat the old bullets. Probably not what you want to hear though.

Thanx Gary. 40 72.

Depending on Cartridge, if it's a full box in good shape it may be worth more to a collector than as shooting ammo.

Photos would help.

Not very old but worth more to collector than shooter

It's a full box but for 2 that have been shot and reloaded.
The brass is tarnished badly . If I can ,l will photo. I shot some bullets one time awhile ago ,that likely were not as old and the necks split on those. They were Herter's Brass ,probably just brittle from age. The problem with that is, the hot gas escaping out beside the bullet in the neck will easily burn the chamber and extraction woes and more neck splits will happen to what may have been a good chamber in a classic rifle, that now needs a major overhaul. Therefore I think I'll keep them for measurements of right bullets made for that caliber ,not shoot them at all and clean them up with brasso.

If keeping them for posterity/collectibility forget the Brasso. Eventually a collector somewhere will howl in anguish when he sees them.

I had some old RemUMC's in the original loading. Some of them split. Thought the 99 had chamber issues. It didn't, old brittle ammo.