How long should my .300Win. Mag. barrel produce best accuracy? I've shot about 200 rounds through it. I've heard about 1500.

Barrels generally burn out rather than wear out...they erode from the breech. the more powder you burn (given the same pressure max) the faster they burn out.

Given a slow rate of fire (not letting the rifle seriously overheat) and good cleaning practices, 1500 is much too pesimistic...something like 2500 to 3000 would be a more like it, although some rifles seem to go much more before showing any serious accuracy proablems.

One "trick" is to switch to longer/heavier bullets...won't cure the erosion, but they seem to shoot better as the barrel breech gets eaten away...at least for a short time.

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Know you've heard the "moving your finger theough a candle flame" anology to expain why the high heat of firing a round doesn't deposit that much heat into the system. One way to look at case volume is to think of it in terms of candles...if 30gr. is "finger passing through one candle" then 60gr. is "finger passing through two candles". The more candles, the hotter that finger gets.

Which is why the big cases heat a barrel up fast...so shoot slower and let it cool when it gets hot, your rifle will live longer.

Wow, thanks for the reply. This is just a hunting rifle so if I can get her to shoot 1/2", I can wear her out to 1" groups and still shoot game twice as far as you need to. Sounds like a lifer. I mean who shoots a .300 magnum for anything short of serious business and enough practice to stay deadly.

Also get a bore guide and a coated cleaning rod. A cleaning rod will wear out your barrel as fast shooting OR NOT CLEANING IT will if you don't have a good guide.

It is my understanding that most of the heat that is generated in a barrel is due the friction of the bullet being swaged through the bore.
Barrel wear comes primarily from the unburned powder eroding the leade and bore. Think 220 Swift. Shooting lighter powder charges will slow down this erosion drastically. As the wear begins to show you can extend the rounds a few thousands to make up for this or have the chamber cut and reset by a gunsmith.
A good cleaning technique will also make all the difference in the world.

Most folks worry 'way too much over barrel wear. The barrel begins wearing out at the first shot, and the wear continues with every subsequent shot. If you're shooting in big-league benchrest competition, your barrel may be "ruined" after only a couple of thousand rounds -- while still being capable of well under MOA accuracy. But I doubt you or your great-great grandson will ever "wear it out" for hunting purposes.

When I shot out the original barrel on my M1A, it had been grouping about 0.75 m.o.a. from prone position. Then, about every 20th shot, I would get an un-called flier about 1.5 m.o.a. from the center of the rest of the group. I thought it was me, but as I kept using the barrel, it became one flier every 10 shots, then one every 5 shots. The majority of the fliers where high and left, but some randomly showed up all around the clock. So, it wasn’t that barrel wear gradually opened groups up. Instead, the 0.75 m.o.a. barrel jumped to being a 3 m.o.a. barrel part of the time, and would eventually have been 3 m.o.a. all the time. If I had been shooting 3-shot groups instead of 20 shot groups on targets, I might not have noticed it until long after the barrel needed replacement. On the occasions the fliers hit, I might well have thought the sights had shifted or oil had got into the bedding or whatever.

Barrel wear is caused by several factors, the three most significant (IMHO) being heat stress cracking, erosion, and corrosion. Corrosion is the oxidation of steel alloy constituents due to chemical reaction with the hot powder and propellant gases under high temperatures and pressures. Note that high temperatures and pressures change the properties of some materials. Glass, for example, will dissolve in water under high temperature and pressure conditions. Stainless steel loses a lot of its corrosion resistance under those conditions. Erosion is the physical abrasion of throat by hot powder and combustion products, and also by bullets, dirt, and anything else that blows down the tube. Heat stressing: even though exposure to heat is brief, it is very intense (4500 degree range) and, unlike a candle, is at high pressure, which puts the heat into the metal surface very rapidly. Even though the metal isn’t exposed to this long enough to melt, it still can’t carry heat away fast enough to prevent the surface from expanding more than the underlying metal. The result is the alligator skin heat stress cracking pattern that is the most visible feature of a worn throat using a bore scope. Hot metal is more easily stressed and oxidized and weaker, so hot barrels were faster. An alligator texture increases metal area and has a stressed surface that is more readily abraded and damaged and chipped away than smooth metal surfaces.

The heat and erosion factors become apparent at the muzzle, too. Especially those of high case capacity rounds. Bruce Baer wrote about this in Precision Shooting a few years back in an article about his .416-based .300 Baer Magnum rifles. Burning a lot of slow powder at high pressure means there is a very large mass of combustion products under very high pressure when the bullet exits the muzzle. The pressure blows the gasses out, imparting a good bit of inertia to them, so they coast out of the tube, leaving a partial vacuum behind. As fast as the inertia is spent, the hot gas and particles in the vicinity of the muzzle are shoved back in. This gradually wears a funnel into the muzzle. It is much like cleaning rod muzzle wear, except it isn’t just the lands getting worn, but the grooves as well. The big guns on battleships have valves in the chamber that open and let air in to fill that vacuum. The cold air rushes in and sweeps the barrel out and avoids the return of the muzzle gasses that cause erosion. The valve inlet air is what blows the smoke ring you see following the main barrel blast in films of these guns firing.

Cleaning rod wear is most apparent in military semi-autos that can’t be cleaned from the breech. It is most pronounced when sectioned cleaning rods are used because the sections act like dull file teeth. Coated rods won’t abrade a bore, but some people claim the coatings become imbedded with dirt that does. The same is said of aluminum rods, since aluminum is easily embedded by abrasive particles. The people expressing these concerns prefer a one-piece stainless rod they can wipe clean after each pass. Whether you use a coated rod or a stainless rod (and I use both, finding the coatings just fine if I don’t carry them outside or to the range where the dirt is). However, if you are cleaning from the muzzle, regardless which rod you use, employ a muzzle bore guide. These are available for all the military self loaders from Sinclair or other dealers in target competition gear.

How long should my .300Win. Mag. barrel produce best accuracy? I've shot about 200 rounds through it. I've heard about 1500.

In the extreme accuracy game of 1k BR a 300 Win Mag barrel has a normal life of 1000- no more than 1500 rounds. Now that is .5 MOA at 1k though. The only magnum that seems to be able to beat that is the 300 WSM that is running into the 2000 plus range normally before it loses its competitive edge.

As for rechambering, DO NOT do it without checking the barrel with a borescope. When rechambering is called for you normally have "firecracking" of the metal away from the bore. How far that extends down the barrel is the key to decide IF there would be enough barrel left after getting rid of all the firecracking. Spending $150-200 to set back a shot out barrel is not wise many times.

BH

I'd like to thank everyone who replied. I value this info greatly and it doesn't seem as though the popular opinion thinks I'll wear out my rifle hunting. That gives me the confidence to practice.