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.338 Edge throat erosion

 
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  #1  
Old 09-15-2010, 03:44 AM
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.338 Edge throat erosion

Can anyone advise me how many rounds it would take in a .338 Edge before
throat erosion starts to effect muzzle velocity?

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Old 09-16-2010, 02:44 AM
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Re: .338 Edge throat erosion

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Originally Posted by Topshot View Post
Can anyone advise me how many rounds it would take in a .338 Edge before
throat erosion starts to effect muzzle velocity?
Less than a 338 RUM, more than a 338-378 Weatherby. Neither of those are as bad as a 264 Win Mag or a 7mm RUM for throat erosion. There are lots of variables including the specific loads, rate of fire, and even the ambient temperature.

But why be concerned? Barrels are made to be replaced. The cost of a new barrel won't be close to the cost of the ammo it will take to burn it out.
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Old 09-16-2010, 05:21 AM
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Re: .338 Edge throat erosion

Lou.
Been noticing the bullets hitting lower on the target of late out near 1000 yards.

Load is 93gn H1000 behind the 300gn SMK. Rifle has fired just over 400 rounds.

I have checked 100 yard zero and load is unchanged from when trajectory was validated.

I shoot at a private area and on a regular basis. All atmospherics etc are taken into account.

I buy bulk boxes of SMK's and H1000 is from the same batch.
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Old 09-16-2010, 10:06 AM
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Re: .338 Edge throat erosion

I have just over 1000 rounds down mine and velocity is still the same as it always has been. I run the same load as you...93 gr H1000, 300 SMK
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Old 09-16-2010, 11:04 AM
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Re: .338 Edge throat erosion

Topshot: What is your cartridge overall length? I ran a Quickload simulation on the Edge case (it assumes 113 grains case capacity) with the powder weight and bullet you stated and it show serious overpressure. But I suspect you have the bullet seated well out from the 3.6" COAL that Quickload has in it's database.
Could you give more details on your load?
Specificially the case capacity of your brass (grains H20 to fill level with the mouth)
and your cartridge overall length. Running overpressure loads will seriously shorten barrel life of most barrels using high performance cartridges.

Throat erosion is very non-linear. Throat erosion is the result of the hot propellant gas raising the temperature of the surface of the throat momentarily (for about two milliseconds up to the point where the steel softens. The propellant gas is not only very hot but also very dense and can push molecules off the surface of throat (which is exposed longer than the rest of the barrel) Barrel life drops rapidly once the steel peaks at a critical temperature. Thermal conductivity of steel is poor, so it's only a very thin layer which is lost with each shot near the onset temperature. Raise the temperature, pressure, or duration a few percent and a barrel can be blown out in a few shots. High performance cartridges push that limit. Those which exceed aren't popular.

The temperature rise for each shot is relative to the barrel temperature at the time of firing, Rapid fire or a high ambient temperature can have a significant effect.

Inspect the throat with a bore scope. Erosion is easy to see and identify.
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Old 09-16-2010, 07:11 PM
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Re: .338 Edge throat erosion

Quote:
Originally Posted by LouBoyd View Post
Topshot: What is your cartridge overall length? I suspect you have the bullet seated well out from the 3.6" COAL that Quickload has in it's database.
Could you give more details on your load?
Lou,
My cartridge OAL is 3.920"
Not sure of the case capacity in H2O but it is a standard .338 Edge case using Remington .300RUM brass.
The chamber was long throated to suit the 300gn SMK when first cut.
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