Thanks! The reason I asked is that today I tried to shoot off some old .30-40 Krag ammo, and NONE of them went off! The rifle functions perfectly, and I've had no trouble with other rounds.
This was Rem-UMC commercial ammo, designated ".30 Govt", and from the look of the box I'd say it was from the 1950s. It looked good, with no visible corrosion. The primers were definitely hit hard and deep enough to fire off a cartridge, but no luck.
Maybe it was stored in a wet basement...!