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Old December 24, 2012, 01:53 PM   #8
wyop
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Join Date: July 15, 2012
Location: Wonderful, Windy Wyoming
Posts: 133
Barrels last according to how hot the ammunition they're shooting is loaded and how hot the barrel gets. The net:net is that over the entire lifetime of the barrel, perhaps bullets are travelling in the bore for all of 2+ seconds. That's the lifetime of a typical barrel.

For rifles like the Garand, which were fed a steady diet of ammunition that isn't all that hot (as .30-06 loads go), the GI barrels lasted quite a while. My copy of Hatcher's "Book of the Garand" is packed up right now, but I seem to recall a War Dep't test cited therein where the barrels were good for 7,000 rounds (plus or minus) for the WWII spec barrels. I'll try to find that book and look up the barrel life tests they ran. The Hatcher book on the Garand is quite interesting and for Garand fans, I'd recommend at least trying to find it in a library and having a read through it.

Rifles that are set up in high pressure rounds (like your Father's 7mm RemMag) and are loaded at the maximum end of the range start seeing throat erosion anywhere from 1,200 to 2,000 rounds - and your estimate of 2,000 rounds is right in the range where a 7mm RM might well see throat erosion. Some cartridges are notorious for burning up barrels - like the .264 WinMag. 1,200 rounds was typical. The .284 Winchester - again, notorious for short, 1,200 round barrel lifespans. Some cartridges have barrel lifetimes in the 10's of thousands of rounds - eg, the .22LR. A .30-06 loaded to M2 ball ammo specs should see lifetimes in excess of what you're seeing in 7mm RemMag. If you hot-rock the -06, then sure, you're going to see throat erosion more quickly.

Do you need a *new* barrel at this point on a rifle like a Rem700 or other bolt gun? Maybe not. You can ask a gunsmith to "set the barrel back" by one turn. This means the tenon is cut back, the chamber is set deeper (by the length of one turn of barrel tenon pitch) and this deeper chambering set-forward usually eliminates the erosion in the throat area. The problem usually becomes that there is a pretty large gap opened up between the barrel and the stock that looks like crap, but the barrel will shoot reasonably well for awhile.

For chambering a short-cut barrel with chrome lining, it might be possible to leave the throat alone and just move the headspace datum forward by using a reamer that has no cutting edges in the neck & throat area - ie, it cuts only in the body of the case and the front of the shoulder area.

On a rifle like the Garand, M1A/M14 etc, you've got a much more complicated barrel installation issue, due to the gas system and the fittings attached to the barrel for the gas system. Setting the barrel back by a turn isn't an easy option.

Chrome lining of barrels is done to make them resistant to both less than ideal maintenance in high moisture environments and rapid rates of fire (eg, military operations in such garden spots as swamps, and full auto weapons). For civilian use... unless you're looking for a low-maint weapon, why bother? Stainless would handle most everything a civilian would want for lower maintenance, and it doesn't create issues for your gunsmith. Most chrome plating eats HSS tools for breakfast, and most of us 'smiths are using lots of HSS tooling - because carbide is more expensive to buy, it's more brittle and it's difficult to sharpen in a typical gunsmith's shop. Why do they create a chrome lined barrel for a Garand? I honestly don't know. I guess it's solving some perceived problem - or it's selling well to people who want one. When I say I have no use for a chrome lined barrel, I'm being quite serious - I don't load my ammo to the max pressure end of the spectrum, I don't go in for rapid fire that heats up barrels and on most of my rifles, I might well set a barrel that was shooting well back a turn and extend the life.

Chrome lining acquired a rep for reduced accuracy due to the earlier chrome plating jobs being inconsistent in thickness in the bore. Recent chrome plating in bores is pretty consistent when done well. Still, it's no longer the best solution to the problems it was trying to solve. There are other barrel treatments that have been explored for the same purposes as chrome lining - stellite liners (eg, in the M2 machine guns) and nitriding of the barrels after all machining is done (all chambering, threading, etc), which has been recently explored by some of the benchrest guys with good results. These nitriding treatments have received some very favorable reviews and results in both barrel life and ease of cleaning - but the tooling to cut through the nitrided layer (if you ever wanted to do something with the barrel after nitriding) is very expensive - and most smiths would probably give it a miss.
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