High Velocity Throat Erosion

[RockyMtnMT]

I want to start a thread to discuss throat erosion as it relates to velocity. There has always been the thinking that the higher the velocity of a gun the faster the barrel will wear out. I think this thought comes from comparing slower cartridges to faster cartridges. Like comparing a 300 rum to a 308 win. Obviously one is faster than the other and the faster of the two has much less barrel life. I want to discuss barrel life of the same cartridge loaded at high or low velocity.

The way I see barrel life and how a barrel wears out, is a function of heat and pressure. Cartridges that are more over bore well wear out barrels faster. It is relative to the amount of powder burnt compared to the relative size of the bore. So a 22-250 runs less powder than a 30-06 and burns out a barrel faster. Not because of the amount of powder burnt but because the relative amount of powder to bore size is much higher for the 22-250. So this validates the thinking that overbore cartridges will have less barrel life. The higher concentration of powder burning in a smaller area of throat creates more heat per square inch of bore surface. This all makes sense and is proven out.

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.

 

[powermax]

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[cabelasken]

The longer bearing surface of the heavier bullet will create more temp instantaneously and I believe it will advance the wear on the barrel by 1) temp 2) more bearing or surface area wear. The higher velocity of the shorter and lighter bullet may have some effect on temp also, but being faster and the contact being even more instantaneous may not transfer as much heat. but I think most overbore cartridges wear the barrel somewhat from the unburned kernals being pushed thru the throat at an increasing velocity. I have seen some actually fall to the ground past the shooting bench, so these travel down the barrel doing damage also. Mark Brown of Brown Precision told me that barrels die from heat - no matter how it is occurs. I've gotten over 5000 rounds thru the original barrel in my 284 and another 6000 thru the shillen Mark installed in 2002. Just now groups have opened up to beyond 1/2 MOA.

 

[cabelasken]

Also, the pressure curve from a heavier bullet is extremely different than that from a lighter bullet. As it imparts more back pressure from the increased bearing area, it makes more efficient use of the powder charge, so the curve should peak and stay at a high level for a longer duration thus adding to velocity. That is why when you shoot a short barrel with an overbore cartridge, it is adviseable to use at least a midweight bullet to make efficient use of the powder.

 

[ShtrRdy]

I'm not smart enough to make sense of all this but if we're mostly wondering if velocity is a major contributing factor then consider the 223. It can get a 55 grain bullet going 3000 fps yet the barrel life is rather long. The 223 would be a good example of the lower powder charge, relative to bore diameter, improving barrel life.

 

[elkaholic]

I want to start a thread to discuss throat erosion as it relates to velocity. There has always been the thinking that the higher the velocity of a gun the faster the barrel will wear out. I think this thought comes from comparing slower cartridges to faster cartridges. Like comparing a 300 rum to a 308 win. Obviously one is faster than the other and the faster of the two has much less barrel life. I want to discuss barrel life of the same cartridge loaded at high or low velocity.

The way I see barrel life and how a barrel wears out, is a function of heat and pressure. Cartridges that are more over bore well wear out barrels faster. It is relative to the amount of powder burnt compared to the relative size of the bore. So a 22-250 runs less powder than a 30-06 and burns out a barrel faster. Not because of the amount of powder burnt but because the relative amount of powder to bore size is much higher for the 22-250. So this validates the thinking that overbore cartridges will have less barrel life. The higher concentration of powder burning in a smaller area of throat creates more heat per square inch of bore surface. This all makes sense and is proven out.

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.

I think you are correct in your thought process in general. when it comes to velocity. There are a lot of other factors that affect barrel (throat) wear obviously, but I don't think that velocity, in and of itself, is much of a factor. If you think about it, the velocity of a bullet at say 1/4" in front of the chamber isn't going to vary at the same ratio as velocity at the muzzle. i.e., acceleration takes time! I believe that one of the overlooked things affecting barrel life (and velocity for that matter) is WHERE is the bullet in the barrel when peak pressure occurs? I say this because elapsed time under pressure has to be a factor in moving metal that has been heated and under pressure.
This is a little ofF topic, but to make a point, that is why I argue that equal CHAMBER pressure does not equal the same velocity at the muzzle.
That is why case design affects all these things as well as changing a powder to a different burn rate.
All this happens in milliseconds and it would take someone a LOT smarter than me to explain it, but I base it on a lot of results Ive seen in my tinkering with case design.
The abrasiveness of certain unburned powders have to be a factor in eroding throats as well, by scrubbing the heated metal thats under pressure.

 

[RockyMtnMT]

I think you are correct in your thought process in general. when it comes to velocity. There are a lot of other factors that affect barrel (throat) wear obviously, but I don't think that velocity, in and of itself, is much of a factor. If you think about it, the velocity of a bullet at say 1/4" in front of the chamber isn't going to vary at the same ratio as velocity at the muzzle. i.e., acceleration takes time! I believe that one of the overlooked things affecting barrel life (and velocity for that matter) is WHERE is the bullet in the barrel when peak pressure occurs? I say this because elapsed time under pressure has to be a factor in moving metal that has been heated and under pressure.
This is a little ofF topic, but to make a point, that is why I argue that equal CHAMBER pressure does not equal the same velocity at the muzzle.
That is why case design affects all these things as well as changing a powder to a different burn rate.
All this happens in milliseconds and it would take someone a LOT smarter than me to explain it, but I base it on a lot of results Ive seen in my tinkering with case design.
The abrasiveness of certain unburned powders have to be a factor in eroding throats as well, by scrubbing the heated metal thats under pressure.

This falls in with my thinking exactly. I get asked often by customers if they are going to wear their barrel out by using a lighter faster bullet. The short answer is no. If you go to a bigger cartridge to run the same bullet faster, then yes. The barrel wear has little to do with projectile velocity.

 

[Calvin45]

Velocity itself can't be the problem. Otherwise the worst of the erosion would be toward the crown where it's going real fast, not in the throat where it's just starting

 

[Creedmoor shooter]

To me id think chamber pressure has more effect than bullet speed. Another interesting thought is high energy powders that create alot of heat.

 

[Northkill]

To me id think chamber pressure has more effect than bullet speed. Another interesting thought is high energy powders that create alot of heat.

Like n570

 

[codyadams]

I think one of the biggest factors in any of this is the powder used. Higher energy powders like RL17, RL26, N570, and others known to get top velocity in certain cartridges also tend to be harder on barrels. My non scientific and very possibly incorrect hypothesis is due to maintaining peak pressure for a longer period of time, thus creating more heat in the barrel leading to shorter barrel life. I don't think bullet speed makes much of a difference in a particular cartridge, it think powder choice is the biggest factor. For instance, using H1000 vs N570 in a 300 rum, I would bet my lunch money the H1000 would give longer barrel life. I would think if your shooting a 165 grain bullet going faster or 245 grain bullet going slower, likely wouldn't make a measurable difference.

 

[Mark37082]

Following…. I'm sure there are some metallurgy based engineers that will chime in. Interesting topic!

 

[Calvin45]

Velocity itself can't be the problem. Otherwise the worst of the erosion would be toward the crown where it's going real fast, not in the throat where it's just starting

But I've yet to see any report of terrible erosion in the last 3 inches of a barrel…the first three tho…that i do hear about here haha.

 

[pdog shooter]

I have no explanation, only picture evidence for the discussion. aprox 2000 rounds and still shot pretty good

edit

55gr nosler ballistic, 43.4 SuperF, 26 inch barrel, 3800FPS.
Thats fast for that bullet