The triple seven propellant leaves a portion of itself behind after ignition. Some of it collects as a hard ring just ahead of the breech, making it difficult to firmly seat the next projectile. How difficult depends on the volume of powder fired. The rest of the bore has a coating of hygroscopic fouling that collects and holds atmospheric moisture. How much depends on humidity, and duration.

An unfired charge if left loaded and sealed can remain perfectly serviceable for a long time, but it's also hygroscopic.

It's a great propellant, but is harder to light off than real BP., and the fouling it leaves behind hardens with commensurate effects on accuracy and ease of reloading. I like to use it in cap&ball revolvers, and BP cartridges for handguns.