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Originally posted by NorthSniper:
. . . My Idea at this point is to go with a lighter bullet in my 308 WarBird, 150gr TSX and use Reloader 19 rather than going 180gr and Reloader 25, this I assume will at least slow the process.

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Anybody know if there is any product you can apply to the throat area to stop or slow throat errosion? Thanks for any comments!

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Originally posted by NorthSniper:
...throat errosion ... causes are? Bottle neck magnum cartridges combined with slow burning powders, right? ...

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Originally posted by Old & Slow:
...I also wonder if high pressures and imperfect bores of rifles expedites gas cutting along the barrel as the bullet passes these wide spots?...

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Originally posted by DigitalDan:
Throat erosion is all about pressure.

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From what I have read on the throat errosion story as far as the big magnums go, the main causes are? Bottle neck magnum cartridges combined with slow burning powders, right?

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Originally posted by ricciardelli:


The only way to not cause wear is to not use the item.
The only way to minimize wear is to use the item only in an emergency.

Why should firearms be any different?

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Clearly, it is not just a pressure issue, though pressure must be a factor. Neck a 30-06 down to 223, and your barrel will be quickly gone, even though you run your cartridges at the same pressure. Being seriously overbore does have an effect.

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Originally posted by DigitalDan:
Y'all fellas believe whatever you want; ...

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Originally posted by DigitalDan:
Y'all fellas believe whatever you want; ...

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Anybody know if there is any product you can apply to the throat area to stop or slow throat errosion?

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Expansion ratio is (the) ratio between the total volume of the bore and the volume of the case. It is the number of times the gas will expand by the time the bullet reaches the muzzle. High expansion rations mean good barrel life. Low ratios mean short barrel life.

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...we know by trial that a 35 grain .22 calibre case is about the most efficient, giving relatively high velocity, fair barrel life and good flexibility. By increasing the case size to a little over 40 grains, we get slightly higher velocity but barrel life suffers badly and flexibility suffers.... By increasing the case capacity to a point where the powder charge exceeds the weeight of the bullet, barrel life drops to very few rounds with no appreciable gain in velocity.

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except maybe for the claim that there are no overbore cartridges.

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�the mechanics of a pressure cooker demonstrate the correlation between heat and pressure. Boiling 2 cups of water in an open pot on the stove allows for a maximum temperature of 212.9� F or 100.5� C at sea level. If you put those same two cups of water into a pressure cooker, add and maintain 15 lbs pressure, the temperature can then be raised to 249.8� F or 121� C. This is accomplished just by adding pressure. Nothing else. Adding more water does not increase the amount of heat in the cooker, but adding more weight (i.e. more pressure) will. Thus a reduction in pressure results in a reduction of heat.

If you take the same 2 cups of water and place them in a larger cooker, it will take longer for it to reach the same temperature time-wise (such as Ken Howell�s example of a pressure curve taken from his 220 Howell) than it would in a smaller cooker (such as the 220 swift).�

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Pressure in and of itself cannot be the primary cause of erosion as many cartridges, large and small, have the same peak pressure.

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Ken Howell

Ken Howell, Dept. GA, 407 Spring Street, Stevensville, MT 59870, or call (406) 777-2878.

This question is in reference to overbored .224 cartridges. Given the same bullet at the same velocity, which cartridge would give you longer barrel life?

A. A smaller case, using less powder but with higher pressure or................
B. A larger case, using more powder but at lower pressure

what do you think?

Now here's a case where I HAVE to correct a term you've just used, not to scold you but to clarify (for you and all others who may read this) � because it's a term so widely and badly misunderstood. So please don't take this as personal � it isn't � it's purely technical, and this little explanation is vital to full understanding of the answer to your question.

The term "overbore" is a corruption of the original "over bore capacity," which in turn rests on the term "bore capacity."

"Bore capacity" for a given cartridge is the net powder space, behind the seated bullet, just roomy enough for safely using a case-filling charge of the slowest available powder. Or it can be used to refer to the net powder space behind the seated bullet FOR A SPECIFIC POWDER.

"Over bore capacity," in reference to a specific powder ("The .220 Swift is dangerously over bore capacity for Unique," for example), means that a case-filling charge of Unique is too much. "Over bore capacity" in reference to a cartridge in terms of its design, without specifying a powder, means that a case-filling charge of ANY available powder is too much(Emphasis mine).

This means that a cartridge that was "over bore capacity" when the slowest thing we had was surplus 4831, while it's still over bore capacity for 4831, is no longer per se "over bore capacity" if there's a canister-grade powder that you can fill the case with, without boosting pressures too high. My .220 Howell, for example, would've been "over bore capacity" when 4831 was the slowest available (and still is over bore capacity for 4831) but (a) isn't over bore capacity for IMR-7828 and a few others and (b) is under bore capacity for Hodgdon 50MG.

Now to answer your question ("Given the same bullet at the same velocity, which cartridge would give you longer barrel life? A. A smaller case, using less powder but with higher pressure or................ B. A larger case, using more powder but at lower pressure what do you think?")

What I think is merely what I fortunately know to be true � because ballistics science has shown it to be so. The answer lies right there in your question � the cartridge with the lower pressure.

This is the basis of a few dozen of my cartridge designs, in fact. The PEAK pressure (actually the peak temperature irremovably connected to the pressure) is what erodes throats � proven, not a private Ken Howell notion.

Wish I could post here some comparative pressure curves I have � the pressure curves for a maximum .220 Swift load and a moderate-pressure, barrel-coddling .220 Howell load. You'll just have to try to imagine 'em from this description:

� The .220 Swift curve for a faster powder and lighter bullet rises steeply to a high, sharp peak just under the red line, then immediately drops off steeply to a rapidly waning low curve to a muzzle pressure noticeably lower than the next curve.

� The .220 Howell curve for a slower powder and heavier bullet rises more gently and gradually, to a longer, lower peak, then tapers off more gradually to a higher muzzle pressure than the other curve.

The Swift curve goes high � HOT � and rapidly erodes throats, while its net volume of expanding, propelling gas is smaller than that of the Howell cartridge.

The Howell curve doesn't go as high or peak as soon � NOT nearly so hot � so it doesn't erode throats as soon, while its greater volume of propelling gas (a) starts the bullet moving more gradually yet (b) accelerates it faster than the smaller volume of gas from the Swift charge would.

To drive any bullet faster than X ft/sec, you have to light-off more powder behind it � but not necessarily in the same powder space. The greater amount of expanding gas behind the bullet accelerates it to a higher exit velocity than a smaller amount of gas could give it.

� If you load the heavier charge in the same space, you raise the pressure.

� If you load the same heavier charge in a larger space, it produces a lower peak pressure.

� Somewhere between lies the happy medium that I seek and that I design for � a larger space to accommodate a heavier charge (usually of a slower powder) that drives the same bullet faster or (better still) a heavier bullet with a better ballistic coefficient at the same or lower velocity, but at a lower peak pressure.

The lower peak pressure is the key.

All this has been well known for decades but not published enough to counter the hype of high velocity as the major criterion for judging performance. My everlasting personal gratitude goes to the late Homer Powley for pointing this out so clearly about forty years ago, long before I came to understand how it works.

It's just too bad that the high-velocity, maximum-pressure fetish has become an obsession for most shooters.

Some shooters pooh-pooh the idea of choosing a magnum cartridge and then loading it to moderate pressures. They're looking through the microscope wrong-way-to. Looking the other way, I see choosing a desired level of performance, then choosing a slightly larger cartridge that will deliver it at moderate pressures, rather than a smaller cartridge that can deliver it only at seam-straining, throat-eroding pressures.

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Ken, I'm going to state this another way, because these guys just don't seem to get the principle. I have no interest in which cartridge is better, but I do understand the physics involved. There's a physical chemistry equation that governs pressure, volume, and temperature. It goes PxV=NxRxT Pressure times volume equals amount of gas times constant times temperature. Given a particular substance, the constant is the same. The volume and the space they take up initially are proportional, so they drop out of the equation. The Temperature of the burning gas is then proportional to the pressure only. The higher the pressure, the higher the temperature. Temperature is not the same as amount of heat. A match is hotter than a bathtub full of hot water, but has a lot less heat. It's the peak heat, which is hotter than the melting point of the steel that damages the steel surface. It doesn't melt the whole barrel, because it only lasts for a few milliseconds while the pressure is highest. However, higher temperatures will damage the surface more. The hotter temperature we feel on a barrel after firing a larger cartridge is only an indication of the overall heat put off by the cartridge, and not of the peak temperature reached. A good example of this is my black powder cartridge rifles. They fire upwards of 85 grains of powder. Barrel heats up a lot more than my 264 mag with 55 or 60 grains of smokeless. However, the 264 concentrates the heat on less surface, and has a higher peak pressure (temperature). Guess which has the lowest barrel life? Slow powders and large case capacities lower peak pressure and increase the volume the gas expands in. This, through the PV=NRT equation equates to a lower temperature. This equates to less steel melting/erosion. Doesn't necessarily make a better cartridge depending on your point of view, but does change the wear on the barrel. Thanks for your patience, Ken, in trying to explain this for all our benefit. Don't let anyone with limited knowledge and a chip on their shoulder drive you off, we appreciate your reasoned input. Dave

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Show me a commercial cartridge that reaches peak pressure before the case is full of H-50BMG and I will show you a cartridge that is 'overbore'.

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I do understand the physics involved.

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It goes PxV=NxRxT Pressure times volume equals amount of gas ....

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That's indeed a true formula, but it applies only to monatomic ideal gasses. It doesn't even work with pure nitrogen or oxygen, because they are diatomic. When you start talking about polyatomic gasses found in a comubustion chamber, it is not a good model at all.

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It is true that pressure and temperature are intimately related, but the pressure cooker example is an awful exaggeration. If you want a more correct example, look at what happens to pressure, volume, and temperature in a diesel engine.

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Yes the pressure cooker is an exageration/simplification. That is due to the target audience it was aimed at. Some wont read past the first line should it contain technical jargon and formulas. I for one would like to hear the better explanation using the diesel engine, but do try to dumb it down for me .

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I hope you have room to welcome this long excerpt from the Powley & Howell book "Inside the Rifle" (Copyright � 2001, Dr Kenneth E Howell), Chapter 15, "Pressure and Erosion."

NB: In this interim version, Homer uses "pounds per square inch" to refer to what we now call "copper units of pressure." Homer wrote the original manuscript a looooooong time ago!

"A bullet in a rifle barrel travels at a higher velocity near the muzzle than at the breech, and we might expect that more wearing (erosion) might occur nearer the muzzle.

"However, we have already studied the fact that the highest gas pressures (and therefore the highest temperatures) occur during the first few inches of the bullet�s travel. The temperatures are high enough to melt steel, so we should expect that at least a very thin film of steel would melt on the surface of the rifle bore where it is exposed to the high-pressure, high-temperature gas.

"The velocity of the bullet increases rapidly, and the molecules of the powder gas follow the bullet with the same velocity, so we would expect this stream of gas to wash some small quantity of molten steel along with it. Also, nitrocellulose gas at a pressure of 45,000 pounds per square inch has an average molecular velocity of about 5,000 feet per second.

"During the time the pressure is high enough to keep the temperature above the melting point of steel, this molecular bombardment scours away any molten surface. By the time the bullet and gas have traveled a few inches past the point of maximum pressure, the temperature of the gas has dropped, the gas is no longer melting the surface of the steel, and the only melting effect that remains is the amount caused by the scrubbing friction of the bullet against the surface of the bore.

"The severe erosion noticed in high-velocity rifles seldom occurs in low-power rifles, because the low-power rifles do not operate at pressures high enough to produce temperatures high enough to melt the surface of the steel. Occasionally, a very �hot� double-base powder used in a low-pressure rifle produces some erosion for a very short distance in front of the chamber.

"We often read or hear that �high velocity causes very rapid erosion and short barrel life.� If this statement were strictly true, we would expect the erosion to be most noticeable at the muzzle, because that is where the velocity is the highest, even though sliding friction becomes less as velocity increases.

"The real reason for rapid erosion is the high temperature produced by the pressure customarily used to produce the high velocity. As an example of using pressure to produce velocity, let�s consider a load of 36.3 grains of a double-base powder in the .300 Savage cartridge. With a 150-grain bullet, the pressure is about 45,000 pounds per square inch, and the velocity is 2,530 feet per second.

"There are two ways to increase the velocity of the 50-grain bullet to 2,700 feet per second.�

"One way is to increase the powder charge to 39 grains in the .300 Savage case. In the .300 Savage case, the pressure becomes 49,500 pounds per square inch.

"The other way is to increase the powder charge to 44.0 grains and load it instead in, say, the .30-06 case. In the .30-06 case, the pressure remains at 45,000 pounds per square inch.

"The muzzle velocity is now 2,700 feet per second, but the maximum temperature in the .300 Savage barrel is at least 450� Fahrenheit higher, and the erosion proceeds much faster. The maximum temperature in the .30-06 barrel is of course unchanged, since the pressure that produces it is unchanged. If one made these increases in the powder charge without knowing and considering the pressures involved, he is likely to reach some erroneous conclusions.

"A shooter would fire several hundred rounds with the .300 Savage before noticing the increase in erosion. The usual conclusion would be that the increased erosion would be the result of the increase in velocity from 2,530 to 2,700 feet per second, in spite of the fact that 2,700 feet per second in the .30-06 produces no more erosion than 2,530 feet per second in the .300 Savage.

"Again, we have another example of the importance of pressure in relation to temperature and erosion. We have been considering 45,000 pounds per square inch as a practical maximum for most high-velocity rifles, because this level of maximum pressure produces good energy per grain and reasonably long barrel life. Safety at this level of maximum pressure is not a serious concern, as it must be when the maximum pressure approaches 60,000 pounds per square inch in modern military-type rifles.

"We have already discussed, in the beginning of Chapter 5, the importance of the relationship between the surface area and the volume of a substance to be ignited by the heat it absorbs from another source. The same relationship applies equally to the granule sizes of gun powders and to the relative dimensions of rifle bores.

"A relatively high ratio of surface to volume means a relatively fast transfer of heat.

"A relatively low ratio of surface to volume means a relatively slow transfer of heat, whether the transfer is from primer gas to powder granule or from powder gas to barrel steel.

"In a relatively small bore, the ratio of the bore�s surface to its volume is greater than the corresponding ratio in a larger bore. The transfer of heat from the hot powder gas to the relatively cooler steel therefore occurs correspondingly more rapidly and erodes the bore more rapidly than gas at the same pressure (therefore the same temperature) erodes a larger bore. At any given level of pressure, therefore, with all other contributing factors consistent, the smaller bore erodes with a lower number of rounds fired, while the larger bore accommodates the same or a larger number of rounds without eroding as rapidly as the smaller bore.

"Here, we have not only another example of the importance of the relationship of pressure to temperature and erosion but also another reason to maintain peak operating pressures well below safe maximums.

"The pressure of the powder gas increases in direct proportion to the confinement of the powder. Increased confinement increases the pressure. Confinement can be increased in either or both of two ways � by an increase in the amount of powder, a decrease in the volume of the container, or both. Whatever the mechanism of the increased confinement may be, it produces a higher pressure, which in turn produces a higher temperature.

"As we have already discussed, the great heat developed within typical cartridges erodes barrel steel. This heat is a direct product of high pressure, so it is the high pressure � the result of powder gas stubbornly expanding against reluctantly yielding resistance � that in producing the heat is the ultimate cause of the erosion of the bore."

"...heat (quantity, measured in Btu) is not the same as temperature (quality, measured in �F or �C). More powder � you're right � does produce more heat (Btu). But burned in a space enough larger, it produces a lower peak temperature (�F) � and it's the higher �F that burns barrels out quicker.

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