The friction in an engine is a totally different situation. First of all, the cylender, pistons, connecting rods, bearings, journals, etc...ar all made of similar hardness metals, usually iron or aluminum, but because their hardness is similar a lack of lubrication, coupled with both the persistant heat of conbustion and the heat generated by friction, combined with the heavy force loads, will cause an engine to wear out. How fast it wears depends on how hard its run. A piston or cylender is nowhere near as hard as the steel in the barrel of a smokeless firearm, not even close. At the same time, the copper or guilding metal over a lead core, or even a pure copper bullet, it much softer than even iron or aluminum. Not to mention the fact that many metals, like copper, lead and brass, are "self-lubricating" to a degree because they are so malleable and ductile (ever hear of a brass bushing? Copper, brass and lead also will not emit sparks when rubbed on another metal, if you'd even been inside the turret and powder magazine of a WWII battleship you'd see that just about every metal-on-metal surface is brass to prevent metal sparks which could ignite the powder bags). With a copper jacketed bullet, the copper yields to the steel, not the other way around. Like Roskoe said, and I will concede this point, like any other surface to surface contact, the copper will eventually, over many tens of thousands of shots, wear the rifling a tiny amount, but the time it would take to create any detectable wear is generally well beyond the service life of the throat of any barrel. The throat will erode thousands of rounds before the rifling further down the bore erodes, and will have the greatest negative effect on accuracy. Once the throat is shot out, the barrel is toast unless it is a straight taper barrel like the one Roskoe mentioned. If bullets were made out of iron or anything other than the mildest steel, then actual bullet wear would be a serious issue. In fact, many eastern bloc countries used actual mild steel jackets for their bullets for lack of copper and zinc to make guilding metal. However, to preserve barrel life the bores were usually chrome plated. Chrome is much harder and wear resistant than mild steel, which meant the barrels would last beyond a few hundred rounds.

If you don't believe me, go find a gunsmith with a borescope and have him show you how a bore erodes. You'll see that while the throat is gone, the rifling just 2-3 inches forward of the throat shows no detectable wear. It's the truth, go see for yourself.

Mike