Army gun barrel erosion and coating programs

Long-running Army effort to deposit structural coatings on gun-barrel interiors to combat propellant-driven erosion. Current production solution is electroplated chromium ("they know there are better materials but nothing as cheap"); vapor-deposition routes all tried.

So yes, you can think of things — like the Army and gun barrels, where you're trying to lay something down on the inside. The Army's developed all kinds of techniques over the last 100 years. Right now the big thing is chromium — they just electroplate chromium on the inside. They've tried all kinds of vapor deposition. They know there are better materials than chromium, but there's nothing as cheap.