Barrel heat and throat erosion - 05/01/02
Ever since Charlie brought up this article for Precision Shooting about barrel heat and throat erosion, I have been chomping at the bit to get it. The mail being what it is, I didn't get the April PS until today. I eagerly read the article as soon as I could.
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<br>To summarize, Mr. Murphy said that shooting the barrel when hot won't cause throat erosion. He said large doses of slow burning powder, friction, the type of barrel steel, shallow throat angles, and the number of shots fired are the factors. This does make sense. I am trying to reconcile it with my experience.
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<br>I had a stainless Sendero in 7mm Rem mag. I would shoot a string of five, then let the barrel cool. In 400 rounds I eroded the throat .040," the accuracy went to pot along with the velocity. The throat should not have eroded that fast. The barrel was 416 stainless, which acceding to the article, is supposed to be the most prone to throat erosion--it may have also been a bad (ie, high sulfur content) batch of steel. The 7mm Rem mag has a throat that seems to promote erosion. That may be due to a shallow angle. Another factor is the turbulence point of this chambering is outside the case neck. This means the hot gases and powder particles are directed to the throat of the rifle instead of the neck of the case. Most of the rounds I fired were loaded with large doses of slow burning powder and heavy bullets. I guess there is enough here to say that shooting it when the barrel was hot didn't hurt?
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<br>I also had an M-1 Garand in 30-06 with Barnett (Douglass blank) chrome moly barrel. It eroded the throat .020 in about 300 rounds. I would fire this gun 10 times in a row before letting it cool. The 30-06 case is not over bore, the barrel was not stainless, the turbulence point of a 30-06 is inside the case neck, and I used medium weight bullets with a medium burn rate powder. I do not know what the throat angle was. I've read where the first few rounds fired through a new barrel "nitride" the throat. Before this occurs, the throat can be easily eroded, but after, the erosion slows dramatically. I didn't do enough testing to verify that with my 30-06.
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<br>I also has a stainless Sendero in 300 Win Mag. The throat eroded .010" in 825 rounds. I seldom shot this when it was hot (have done it once or twice).
<br> I used slow powders with medium weight bullets. The 300 Win is not as overbore as a 7mm Rem mag. I don't know what the throat angle is, but the turbulence point is outside the case neck.
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<br>I also have some custom barreled guns--all stainless. One barrel was a Shilen, one an Apex, and all the rest Pac-Nors. I haven't had any throat erosion in these guns yet. I seldom shoot them when they are hot (have done it once or twice). The 30-06, 340 Wby, 375 Ack, 416 Rem, 338 Win, were/are not overbore at all. The 338 Ultra is about like a 7mm Rem Mag in terms of being overbore. I also have another 300. I had/have less than 300 rounds through any of these rifles. Maybe the quality of stainless steel is better than the factory offerings, and I know John Rick's work is better than factory work. All but the 300 have the turbulence point inside the case neck. Perhaps the throats all have sharper angles.
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<br>Maybe I can shoot them hot. I wonder which gun I should try it on?
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<br>Blaine
<br>
<br>To summarize, Mr. Murphy said that shooting the barrel when hot won't cause throat erosion. He said large doses of slow burning powder, friction, the type of barrel steel, shallow throat angles, and the number of shots fired are the factors. This does make sense. I am trying to reconcile it with my experience.
<br>
<br>I had a stainless Sendero in 7mm Rem mag. I would shoot a string of five, then let the barrel cool. In 400 rounds I eroded the throat .040," the accuracy went to pot along with the velocity. The throat should not have eroded that fast. The barrel was 416 stainless, which acceding to the article, is supposed to be the most prone to throat erosion--it may have also been a bad (ie, high sulfur content) batch of steel. The 7mm Rem mag has a throat that seems to promote erosion. That may be due to a shallow angle. Another factor is the turbulence point of this chambering is outside the case neck. This means the hot gases and powder particles are directed to the throat of the rifle instead of the neck of the case. Most of the rounds I fired were loaded with large doses of slow burning powder and heavy bullets. I guess there is enough here to say that shooting it when the barrel was hot didn't hurt?
<br>
<br>I also had an M-1 Garand in 30-06 with Barnett (Douglass blank) chrome moly barrel. It eroded the throat .020 in about 300 rounds. I would fire this gun 10 times in a row before letting it cool. The 30-06 case is not over bore, the barrel was not stainless, the turbulence point of a 30-06 is inside the case neck, and I used medium weight bullets with a medium burn rate powder. I do not know what the throat angle was. I've read where the first few rounds fired through a new barrel "nitride" the throat. Before this occurs, the throat can be easily eroded, but after, the erosion slows dramatically. I didn't do enough testing to verify that with my 30-06.
<br>
<br>I also has a stainless Sendero in 300 Win Mag. The throat eroded .010" in 825 rounds. I seldom shot this when it was hot (have done it once or twice).
<br> I used slow powders with medium weight bullets. The 300 Win is not as overbore as a 7mm Rem mag. I don't know what the throat angle is, but the turbulence point is outside the case neck.
<br>
<br>I also have some custom barreled guns--all stainless. One barrel was a Shilen, one an Apex, and all the rest Pac-Nors. I haven't had any throat erosion in these guns yet. I seldom shoot them when they are hot (have done it once or twice). The 30-06, 340 Wby, 375 Ack, 416 Rem, 338 Win, were/are not overbore at all. The 338 Ultra is about like a 7mm Rem Mag in terms of being overbore. I also have another 300. I had/have less than 300 rounds through any of these rifles. Maybe the quality of stainless steel is better than the factory offerings, and I know John Rick's work is better than factory work. All but the 300 have the turbulence point inside the case neck. Perhaps the throats all have sharper angles.
<br>
<br>Maybe I can shoot them hot. I wonder which gun I should try it on?
<br>
<br>Blaine