Well jeeze, I might as well drain the oil from my car and drive it arround since that contact isn't wearing..
Totally different situation.The oil in your engine does reduce friction but it also carries away heat created by friction which is what will destroy your bearings and pistons.On the other hand the bullet is only in the barrel for an extremely short period of time so other than in the throat area,virtually no wear takes place.
but the faster something moves the more potential it has to cause mechanical errosion.
By the time any significant wear due to friction takes place,the throat will be non existant,so wear due to friction is not a factor in barrel life.