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throat erosion?

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Unread 01-25-2004, 04:41 PM
dwm dwm is offline
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Join Date: Feb 2003
Location: Texas
Posts: 738
Re: throat erosion?

Brian, I think you missed my point. I didn't say the bullets were causing wear on the barrel. I said that the bullets were harder to get moving because:

1. they are heavy for the caliber and therefore harder to get moving forward (probably minimal effect, but still a contributor),
2. have a large bearing surface which is harder to push into the lands and down the barrel, doesn't the bullet deform as it cuts into the rifling,
3. the fast twist also makes it harder for them to get started moving because they are harder to spin up (heavy weight also makes this worse) thet have to move forward and spin at the same time while cutting grooves in the sides,

All these things contribute to the bullet (accelerating) moving out of the throat slower as the powder burns in the throat area.

This causes the flame ball to sit near the throat longer and melt the lands at the throat.

I was not talking about wear, I was talking about the flame ball melting the barrel.

Brent, don't almost all modern powders have a significant graphite content? Wouldn't this reduce the sand blasting effect?

I'm not saying your wrong, maybe it is the sandblasting.

I was trying to get everyone to think in terms of melting the barrel in the throat area. Then the powder and gas flow push the molten barrel metal out of the throat and down the barrel.

Maybe the sandblasting has the advantage of a very hot throat because of all the reasons I stated above.

Ever had an overbore case shoot the throat out of a gun ("early") that has a slow twist and is used only with light for the caliber bullets?

More to think about.


[ 01-25-2004: Message edited by: dwm ]
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Unread 01-25-2004, 05:10 PM
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Join Date: Dec 2003
Location: Stamford NY
Posts: 160
Re: throat erosion?


your right i did miss that last post, I think I can some up everything, With a heavy bullet more thoat errosion happens because the powder burns longer at the throat causing the barrel to become hot and soft and when you throw in the unburned powder hitting the soft metal at high speeds it causes errosion, I dont think graphite would help with the powder hitting the barrels walls, just reduces the friction of the bullet and reduces the time that flame ball stays at the throat.


[ 01-25-2004: Message edited by: Brian Rybicky ]
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Unread 01-25-2004, 06:57 PM
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Join Date: Apr 2002
Location: Pennsylvania
Posts: 82
Re: throat erosion?

how can you tell you have throat erosion. is it obvious looking into the barrel? does it deteriorating accuracy? I have never seen it or experienced it.
300 RUM and a 458 win mag...what more can a man want!
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Unread 01-26-2004, 12:41 AM
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Join Date: Dec 2001
Location: Long Island, New York
Posts: 2,516
Re: throat erosion?


I have always believed that long/heavy bullets had the potential to increase throat erosion for the reasons that you stated. However, long/heavy bullets also require you to use a lighter powder charge than a medium or light bullet in the same cartridge. Lighter charges almost always equate to less throat erosion.

I haven't got a clue as to which has a greater effect on the rate of erosion; medium weight bullets w/heavy charges OR heavy bullets w/medium charges. [img]images/icons/confused.gif[/img]

I shoot em' all and rebarrel when necessary. I have to admit, the "Longrange Hunting" boys sure have me shooting many more of the heavy weights than I ever did before. I use to be one of those light, fast and furious kind of guys. [img]images/icons/grin.gif[/img]


[ 01-25-2004: Message edited by: Varmint Hunter ]
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Unread 02-01-2004, 12:18 AM
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Join Date: Apr 2002
Location: Loon Lake WA
Posts: 362
Re: throat erosion?

Dr. John, most accurate loads fire best when loaded a specific distance off of the lands. This can be measured in differant ways, but as they "erode" away, most precision shooters chase them by loading thier cartriges longer. Some can tell by accuracy becoming degraded. Or check with special tools. Stoney Point makes one. I don't know how good it is, I have never used one. A simple one can be made by using a fire-formed casing in the rifle that fired it. Seat the bullet long, but not too tight (Remember, no powder or primer!). Chamber it, then remove it and measure the length. If the chamber is unusealy long, you will be able to tell. Some rifle manufactures just plain have very long chambers. Its what I call "Factory Throat Erosion." There is more too it than what I have listed, but I think you will get the gist of it. Hope this helps!
Portate bien o te lleva el cucuy
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Unread 02-01-2004, 09:29 AM
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Join Date: Aug 2003
Location: NC, oceanfront
Posts: 4,223
Re: throat erosion?

There is every bullet/twist combination possible out there in STD 308s.
I've never heard of a 308 burning out this side of several thousand rounds.
If I remember correctly, the 6PPC also offers a long barrel life.
No matter what you do with them, they will last longer than a 240gibbs or a 30-378.
And no matter you do with a 30-378, it will not last as long as a std 308.
Much as I hate it, the erosion definitely follows the amount of powder set loose in a given bore area. Pressure, boattail, powder type, dwell,etc, must all have minor roles, as neither, or all, cannot contradict powder AMOUNT away.
In otherwords, a 56grcap Win308 at 60kpsi pressure load will still outlast a 133grcap 30-378Wby. Even if it's loaded to only a 40kpsi pressure load.
I don't understand why. Simple energy amount, I guess.
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