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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Barrel contour
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<blockquote data-quote="GrayCreed" data-source="post: 2398768" data-attributes="member: 114633"><p>My ¢2</p><p></p><p>I think there is more to this than just the contour.</p><p></p><p>I'm not a metallurgist either but my family has a long history or metalworking in machine shops. There is a big difference between stainless and CMV or chrome-moly carbon steel. Stainless is reflective to heat in nature which works against it when it comes to heat disapation unless it's either white or heavily fluted. Stainless (416R) is usually chosen because it is easier to machine and thus you can "run" precision barrels faster through a machine shop resulting in a high quality bore at an affordable price.</p><p></p><p>Chrome Moly is 2-3 times tougher than stainless. This means it's 2-3 times harder to machine and achieve the same smooth bore finish without going slower, using more expensive tooling and lots of coolant. (If you don't use coolant tooling will melt under some circumstances). The toughness of CMV means that the inner surface of the barrel will last longer under heat and pressure. It also means that it will take alot more heat to get things to move (POI shift). Also CMV transfers heat quicker so the heat may travel up the barrel away from the chamber/throat area. The bad part of this means that hand lapping may be required to get the smoothness of the bore to a satisfactory point for accuacy.</p><p></p><p>Processes:</p><p>This is actually the most important point I want to make.</p><p>POI shift often comes because a barrels internal stresses change the barrels directional/radial shape as is heats up. This happens because heat "demagnetizes" the internal magnetic fields in the barrel and allows for the stress to pull this way or that. The most important process to remedy this is stress releaving. Faxon did an exceptional series on this in an interview style with someone a few years back. Cold hammer forging creates the best barrels for heat because the process aligns the stress in the metal in a way that it doesn't whip rounds as much when hot. Col Nutinfancy did a video on the weatherby Vanguard in 308 (Sporter profile barrel) and reported under fairly heavy fire it didn't whip rounds that much! The same is true of my Tika T3X (stainless Cold hammer forged) as far as I know all the sako barrels are CHF. All machine gun barrels are CHF because of this very thing. Also most machine gun barrels are fairly on the Sporter side (M249)</p><p></p><p>If you want to save weight without barrel whip find a barreled action you like that comes with a CHF barrel. If you have the money just buy the sako85. I usually shoot 5-10 rounds out of my Tikka super light 7mag and I stop because the barrel is hot and I care about my bore. If I kept going it would still be shooting 1/2moa</p><p></p><p>Joel</p></blockquote><p></p>
[QUOTE="GrayCreed, post: 2398768, member: 114633"] My ¢2 I think there is more to this than just the contour. I'm not a metallurgist either but my family has a long history or metalworking in machine shops. There is a big difference between stainless and CMV or chrome-moly carbon steel. Stainless is reflective to heat in nature which works against it when it comes to heat disapation unless it's either white or heavily fluted. Stainless (416R) is usually chosen because it is easier to machine and thus you can "run" precision barrels faster through a machine shop resulting in a high quality bore at an affordable price. Chrome Moly is 2-3 times tougher than stainless. This means it's 2-3 times harder to machine and achieve the same smooth bore finish without going slower, using more expensive tooling and lots of coolant. (If you don't use coolant tooling will melt under some circumstances). The toughness of CMV means that the inner surface of the barrel will last longer under heat and pressure. It also means that it will take alot more heat to get things to move (POI shift). Also CMV transfers heat quicker so the heat may travel up the barrel away from the chamber/throat area. The bad part of this means that hand lapping may be required to get the smoothness of the bore to a satisfactory point for accuacy. Processes: This is actually the most important point I want to make. POI shift often comes because a barrels internal stresses change the barrels directional/radial shape as is heats up. This happens because heat "demagnetizes" the internal magnetic fields in the barrel and allows for the stress to pull this way or that. The most important process to remedy this is stress releaving. Faxon did an exceptional series on this in an interview style with someone a few years back. Cold hammer forging creates the best barrels for heat because the process aligns the stress in the metal in a way that it doesn't whip rounds as much when hot. Col Nutinfancy did a video on the weatherby Vanguard in 308 (Sporter profile barrel) and reported under fairly heavy fire it didn't whip rounds that much! The same is true of my Tika T3X (stainless Cold hammer forged) as far as I know all the sako barrels are CHF. All machine gun barrels are CHF because of this very thing. Also most machine gun barrels are fairly on the Sporter side (M249) If you want to save weight without barrel whip find a barreled action you like that comes with a CHF barrel. If you have the money just buy the sako85. I usually shoot 5-10 rounds out of my Tikka super light 7mag and I stop because the barrel is hot and I care about my bore. If I kept going it would still be shooting 1/2moa Joel [/QUOTE]
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