High Velocity Throat Erosion

[sedancowboy]

Great discussion!
Since the barrel erosion is in the throat instead of the muzzle and we assume that most of the powder is burned by the time the bullet gets to the muzzle and is where the bullet is going the fastest then we can assume that powder burn instead of speed is the cause of throat erosion.
There is a lot of energy transfer in a very short time span and space. I see evidence of direct impingement of fire and heat in burned out throats. I do not see evidence of powder erosion by friction in the throat and I do not buy the theory that the powder is wearing the barrel by abrasion. The powder is not a abrasive and most is coated with a lubricant such as graphite. A barrel gets hottest at the chamber end where the bullet is going it slowest not at the muzzle where the bullet is going its fastest. Which leads me to the conclusion that heat from powder burn and not heat from friction is the cause of burned out throats.
So to answer the question I think the type of powder and how it impinges on the throat impacts throat erosion more than bullet weight.

 

[codyadams]

I do not see evidence of powder erosion by friction in the throat and I do not buy the theory that the powder is wearing the barrel by abrasion. The powder is not a abrasive and most is coated with a lubricant such as graphite.

I do believe that graphite can turn into an abrasive when under pressure and heat (ie, kind of how diamonds are made, I think?), I'm just not sure if the specific environment needed occurs in a chamber/barrel during a cartridge combustion to make it abrasive. Well over my head.

 

[Hard rock]

Great discussion!
Since the barrel erosion is in the throat instead of the muzzle and we assume that most of the powder is burned by the time the bullet gets to the muzzle and is where the bullet is going the fastest then we can assume that powder burn instead of speed is the cause of throat erosion.
There is a lot of energy transfer in a very short time span and space. I see evidence of direct impingement of fire and heat in burned out throats. I do not see evidence of powder erosion by friction in the throat and I do not buy the theory that the powder is wearing the barrel by abrasion. The powder is not a abrasive and most is coated with a lubricant such as graphite. A barrel gets hottest at the chamber end where the bullet is going it slowest not at the muzzle where the bullet is going its fastest. Which leads me to the conclusion that heat from powder burn and not heat from friction is the cause of burned out throats.
So to answer the question I think the type of powder and how it impinges on the throat impacts throat erosion more than bullet weight.

When I worked my loads up for my 6.5 prcs I used N 165 for that reason it is one of the coolest burning powders H4350 is next up . I now have a good idea what this cartridge is capable of , am now moving too N 560 all double base powders will burn hotter which in return will be harder on the throat and barrel . All that being said the barrel for a hunting rig would be hard too burn out , unless you are a one rifle owner . Great info on barrel wear ,that all does make sense.

 

[Northkill]

Kirby Allen told me a few months back that he's played around with a forward ignition system that would get his 7 AM from RL33 to a H4831 burn rate. I didn't get permission to post the particulars but basically burns the powder front to back. Dramatic reduction of the pressure curve and no powder through the neck and into the throat. The barrel barely gets warm this way, but the case is hot enough to brand cattle with. Cost prohibitive at this point, but maybe the stuff of the future.

 

[Calvin45]

I do believe that graphite can turn into an abrasive when under pressure and heat (ie, kind of how diamonds are made, I think?), I'm just not sure if the specific environment needed occurs in a chamber/barrel during a cartridge combustion to make it abrasive. Well over my head.

Def not turning into an abrasive at these temps but fair question.

If only I could find a way to turn gunpowder into diamonds tho….ah dang it never mind, if it's RL26 it'll still be a depreciation in value at this point

 

[2buffalo]

In my mind which is often incorrect I wonder if it's the combination of the highest heat (closest to the hottest part of the reaction), the bullet jumping into the grooves extremely fast, and the highest engraving pressure in the first few inches of the barrel? I would guess that all three together in an overbore cartridge would contribute to short barrel life?

 

[milo-2]

What I want to discuss is weather or not increased velocity in the same cartridge changes barrel life. Since I mentioned the 308 win, let's use it for comparison. Let's use a generic bullet for now.

If we load the 308win with a 215g bullet at a velocity of 2450 fps and a pressure of 61,300 psi and compare it to loading a 110g bullet at a velocity of 3450 fps and a pressure of 61,300. Which one burns out the barrel faster and why? I have not tested this and likely never will. It would need two identically built rifles shot sxs and carefully monitored throat wear. My contention is there will be very little difference in barrel wear.

Nothing scientific in my thinking, got that out of the way. In this scenario, all parameters equal, shot for shot, the barrel shooting the heavier bullet barrel would fail first.
My logic being the heavier bullet is in the barrel longer, so also burning powder longer in the particular area where the most damage occurs.
One thing i have learned in shooting is that nothing is linear. Fantastic barrel life of 30 deg 6.5 cases when necked down to 6mm become train wrecks inside barrels. I am also not sold on all high energy powders eroding throats more than other powders. Single case example I got 3900 rds from a 6.5 x 47 barrel shooting 136gr Scenar L's with VV N 550, I pulled the barrel because I wanted to sell the action.
Now I am not talking about hunting rifles, which should last considerably longer than target barrels. But in target barrels, relying on a case design for barrel life can be a myth, my godson toasted a 6 Dasher barrel in 1200 rds. Of course this was clearly a case of not keeping the booger picker off the bang button, but he is still a legend.
Very interesting thoughts by quite a few people!

 

[Calvin45]

Nothing scientific in my thinking, got that out of the way. In this scenario, all parameters equal, shot for shot, the barrel shooting the heavier bullet would fail first.
My logic being the heavier bullet is in the barrel longer, so also burning powder longer in the particular area where the most damage occurs.
One thing i have learned in shooting is that nothing is linear. Fantastic barrel life of 30 deg 6.5 cases when necked down to 6mm become train wrecks inside barrels. I am also not sold on all high energy powders eroding throats more than other powders. Single case example I got 3900 rds from a 6.5 x 47 barrel shooting 136gr Scenar L's with VV N 550, I pulled the barrel because I wanted to sell the action.
Now I am not talking about hunting rifles, which should last considerably longer than target barrels. But in target barrels, relying on a case design for barrel life can be a myth, my godson toasted a 6 Dasher barrel in 1200 rds. Of course this was clearly a case of not keeping the booger picker off the bang button, but he is still a legend.
Very interesting thoughts by quite a few people!

On the flip side, it could be that heavy for caliber bullets are better because they're

a)more efficient as far as foot pounds per grain of powder burned - this is indisputable. Using the same powder you need a higher charge weight to reach the same level of muzzle energy with the lighter bullet. All load data plainly shows this to be true. And I think we're all agreeing the bullet itself isn't what erodes the barrel - otherwise the muzzle end would be more eroded but it isn't.

B) this is more speculative, but it seems to me that the heavier bullet, more reluctant to get going and with more bearing surface to resist engraving, probably results in more of the most intense part of the burning transpiring inside the cartridge case than in the throat and barrel. Probably not by much but still a non-zero effect for sure, it has to be! Would explain a lot. By the time thay big pill has made it X amount down the pipe, the light weight has gone notably farther AND allowed more still-burning powder into the throat (and this out probably a higher charge weight as we discussed).

 

[cohunt]

Even if you could shoot 2 barrels side by side-- each barrel is slightly different metallurgucally.
But comparing 2 side by side equal cartridges--- the lighter bullets typically use more powder than the heavier bullets- so more heat duration in the throat may affect erosion. Most likely it's all about max temp and duration--- the hotter a barrel gets the more erosion it's gonna see is my guess.
In the end, barrels are consumables --- I want accuracy and will do anything to get there regardless of barrel life.

 

[Calvin45]

I also have been coming to believe that lightweights can be loaded significantly hotter pressure wise without showing any pressure signs. Just a theory…based on experience…

Pressure and heat together work as a blowtorch. A 60-75kpsi blowtorch.

 

[Hard rock]

I also have been coming to believe that lightweights can be loaded significantly hotter pressure wise without showing any pressure signs. Just a theory…based on experience…

Pressure and heat together work as a blowtorch. A 60-75kpsi blowtorch.

It seems a longer barrel with a uniform burn rate from the throat too the muzzle would be my powder choice , and should produce the most velocity with less throat erosion. I try too achieve that , and it seems too work when trying too get all the potential out of a given cartridge and bullet weight .

 

[venatic]

Heavier bullets erode throat faster due to dwell time in throat and focusing heat there longer...this was written about by the late Glen Zediker in one of his AR books I believe

 

[Calvin45]

Many of you will have heard of the .22 eargesplittenloudenboomer by PO Ackley (.22-378 wby) but how many have heard of this historic beast!?!? 7.92x107mm anti tank round, Polish…a 225 grain tungsten core 8mm at 4100+ fps out of a 40+inch barrel with over 8000 foot pounds At the muzzle.


I reckon that's gonna erode the barrel from throat to crown haha…make a .30-378 look like a BB gun.

A google search for 7.92x94 patronen or 7.92x107 polish will tell you more.

 

[orkan]

My thoughts on the matter from several years ago.




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