What is the real relationship between bullet velocity and barrel erosion, and what does it mean to you?
Posted: 2004-12

A few years ago former Petersen's Hunting editor Gary Sitton and I were talking about fast cartridges and barrel wear. Quick-witted, Sitton could always produce the best one-liners: "Hell," he said, "when we were kids, just the rumor of being hard on barrels was enough to kill a cartridge. Today it's a badge of honor if you burn out a barrel in one season."

Even today there are only a couple of cartridges that are actually faster than the 70-year-old .220 Swift: the .204 Ruger and the .223 WSSM. But there are a bunch of very fast cartridges out there, including "standard" magnums, WSMs, RUMs, Weatherby and Lazzeroni magnums. Some of the fast new cartridges are selling well, seemingly unhampered by throat-eroding reputations that once nearly killed the Swift and almost certainly aided the demise of the .264 Win. Mag. Was Sitton right? Are shooters no longer concerned about rapid barrel wear, or have barrels gotten so much better that it's no longer a problem?

G&A reader Tracy Arbaugh just sent in a letter that encapsulates the question so well that I think it offers worthwhile reading: "There was a time when throat erosion was talked about in rifles using the super-fast rounds. I notice that some of the speeds of today's cartridges are almost unimaginable, and they seem to be getting faster. Has throat erosion or damage just become a thing of the past, or is it that no one really cares these days? What is the maximum speed at which a bullet can be launched where the rifling can no longer engrave the bullet and keep it spinning?"

Engraving the rifling is not the limit, at least not with current technologies. Depending on alloy, lead bullets skid down the barrel at around 2,000 fps, which is why the jacketed bullet was a parallel development required by the invention of smokeless powder. At velocities possible today, modern jacketed bullets will engrave into the lands and acquire the rifling spin.

The actual limitation is the propellants we use. Burning gases from nitrocellulose powders travel at about 5,300 fps, which is thus the theoretical velocity limit. The practical limit is somewhat lower since the gas must push the bullet down the bore and through the rifling, creating friction and reducing velocity. Very light bullets with limited bearing surface (less friction) can be pushed to very high velocities, possibly exceeding 5,000 fps if you believe some experimenters. But we all know light-for-caliber bullets lose velocity quickly, so the practical tradeoff is longer bullets (more friction) that cannot be pushed as fast but offer better downrange performance.

Another possibility is smoothbore barrels with sabot rounds, as used in the most modern tank cannons--again, less friction and thus very high velocity. Remember Remington's light-bullet Accelerator sabot loads? Man, are they fast, and I suspect they'd be faster yet from an unrifled barrel. Someday the technology that gives superb accuracy in smoothbore tank guns may be common in sporting arms, but I doubt I'll see it.

So, with bullets of adequate weight to provide effective performance downrange--and with cartridges loaded to sensible pressures--I think we're somewhere near the practical velocity limit in the mid-4,000s. Put the right (light) bullet in the right case with the right powder, and sometimes speeds up to 4,400 fps or a bit more can be reached. Realistically, that isn't much faster than what the .220 Swift did back in the 1930s. Unless and until technologies change drastically, I don't think we'll ever see practical sporting-rifle velocities approaching 5,000 fps.

Now, as to barrel wear, modern metallurgy and barrel coatings have indeed increased barrel life. The problem is that no two barrels are alike. None is perfectly smooth, and none is perfectly straight, nor is it of the exact same inner dimensions. So barrels wear at different rates. In other words, one .300 magnum barrel may produce noticeably reduced accuracy at 1,500 rounds (or less) while another .300 with a similar barrel may continue to shoot extremely well at 2,000 rounds or more. So it is impossible to accurately predict barrel life for any cartridge or caliber.

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