Rifle barrel burnout question?

[Roughwater]

It's long been said that speed will kill a rifle barrel.

My question is one that's long been in the back of my mind.

Ok, These are extreame situations so just using them as an example.

Say you have a 270 Winchester rifle generally thought to have long barrel life but you're using it to hunt varmits and using 110 grain bullets blazing along at 3500 FPS.

On the other hand you have a 28 nosler not known for great barrel life but you are using it for big game so you load up with 195 grain bullets at 3000 fps out of a 26", 9 twist barrel.

So which will have the longer barrel life? I'm asking cause I've always assumed it was the speed of the bullet that was the main cause of barrel wear so long as its cleaned and broke in properly. Or do the longer for caliber bullets also accelerate wear even if they are generally kept under 3100 FPS? Also does twist rate affect barrel life much? I'm thinking a 8 twist could wear quicker than a 10 everything else being the same but again I don't really know so am asking. Thanks in advance for your input.

 

[HellsCanyon]

First, barrel life is 99% of the time determined by throat erosion. The portion of the rifling that the bullet first engages the lands/grooves. The throat erodes from the explosion and burning of powder. The lands/grooves of the rest of the barrel will take infinitely more rounds to "wear out" than the throat does to erode from burning powder.

Speed in this case is "relative". I've measured the throat of multiple 28 noslers. A 195 out of a 28 Nosler/26" barrel at UNDER 3050 fps (typically 3035ish depending on barrel and powder) at 500-600 rounds down the pipe will typically have .015" throat erosion.
There's a higher velocity node with that combination that exists around 3125fps-3150fps. Same round count and I've seen throat erosion in the .030"+ range. You effectively reduce your barrel life by 1/2 by shooting that higher node.

Hope this helps.

Mike

 

[Roughwater]

First, barrel life is 99% of the time determined by throat erosion. The portion of the rifling that the bullet first engages the lands/grooves. The throat erodes from the explosion and burning of powder. The lands/grooves of the rest of the barrel will take infinitely more rounds to "wear out" than the throat does to erode from burning powder.

Speed in this case is "relative". I've measured the throat of multiple 28 noslers. A 195 out of a 28 Nosler/26" barrel at UNDER 3050 fps (typically 3035ish depending on barrel and powder) at 500-600 rounds down the pipe will typically have .015" throat erosion.
There's a higher velocity node with that combination that exists around 3125fps-3150fps. Same round count and I've seen throat erosion in the .030"+ range. You effectively reduce your barrel life by 1/2 by shooting that higher node.

Hope this helps.

Mike

Thanks Mike, good to know. So how is erosion affected by going beyond say 3200 FPS?

 

[5MilesBack]

You effectively reduce your barrel life by 1/2 by shooting that higher node.

So, how many rounds can I expect to get down the pipe of a .270 WIN shooting 85gr Barnes at 3900+ fps?

 

[KurtR]

erosion is caused not as much by speed as it is an over bore condition. you are shoving that big fire ball down a small hole. There are also so many other factors like how long of strings you shoot. shooting a .264 win mag slow speeds is still going to erode the throat way faster than a .308 with fast load.

 

[Rthur]

Barrel life for the most part can be semi predicted by powder volume/bore diameter.
Some factors help with the overbore chamberings but not by huge margins.
Case design and "cooler/slower powders" can and do help to some degree.
When discussing "magnums" or magnum like cartridges for hunting it'll take a bit even with a 1500ish barrel life.
Barrel material types can have some effect as well.

R

 

[Wapiti1]

I'll state it a little differently than Kurt and HCA have. Throat erosion is simply the amount of time the throat is in contact with hot combustion gases. The erosion is actually melting and vaporization of the throat area by these hot gases.

Slow powders, big charges and large volumes of combustion gas mean that the throat will be subject to erosion conditions longer, and be eroded more per shot than the opposite situation.

This is also to some degree dependent on the powder. Some powders burn at low temps relative to other powders. If you are a revolver shooter, there is a stark difference between H110 and lil' gun. I have not seen quantitative data on rifle powder burn temperatures, but do know they don't all burn the same.

Speed and weight of the bullet are somewhat irrelevant. I say somewhat because heavy bullets necessitate slower powders that burn longer and in turn set up the conditions for throat erosion. Actual speed of the bullet has no effect.

So, the more overbore, the longer the throat is in contact with hot gas and the more erosion per shot you get.

This is exacerbated by fast shooting, or long shot strings where the throat never recovers to a low temp. It starts at a high temp and takes less energy to get to erosion temps with subsequent shots. The very reason machine gun barrels are often chrome lined.

Jeremy

 

[Roughwater]

Thanks Jeremy. Based on that statement then I would have to think midrange or maybe even bullets on the light side for the caliber would cause less erosion that the heavies? I wonder why hunting rifle throats are not chrome lined then? Seems a cheap SKS I bought many years ago advertised as being chrome lined.

 

[Gatorgrizz27]

Thanks Jeremy. Based on that statement then I would have to think midrange or maybe even bullets on the light side for the caliber would cause less erosion that the heavies? I wonder why hunting rifle throats are not chrome lined then? Seems a cheap SKS I bought many years ago advertised as being chrome lined.

Chrome plating reduces accuracy in most cases, as it cannot be controlled as precisely as machining stainless or chromemoly. My SKS isn’t going to win an accuracy competition against a decent slug gun.

This “issue” is also a relatively new deal with the overbore/long range hunting increase in popularity. Most hunting rifles will never wear out a barrel as even one with a really short life of 1,500 rounds is a lifetime for most shooters. It’s not just going to shoot horribly all of a sudden either, the groups gradually open up and a lot of people wouldn’t even notice. The guys that shoot a lot and compete spend so much $ in ammo the barrel cost isn’t a big deal in comparison.

 

[hodgeman]

Yeah...lots of good comments on this thread so far.

Throat erosion is a function of how much gunpowder you're trying to burn, how fast...and for how long. "Overbore" rounds- where you're really trying to burn more powder than will actually burn in the bore are fairly hard on barrels. There's just a lot of gunpowder burning for the entire duration of the shot and lots of heat transfer to the barrel. Something like a 30-30 might last darn near forever, heck- mine is nearly 100 years old and still shoots great. A real hot number like the 26NOS or 6.5-300WBY might be done in just 500-600 rounds.

Couple of points though- in a hunting rifle, 500-600 rounds is a genuine lifetime of hunting use and even real barrel burners like the .257 Weatherby will rarely ever be shot enough to genuinely burn out. Hardcore competition guys might zing through a barrel per year, but even then...their cast off barrels might still be perfectly acceptable for most hunting applications.

After messing with hundreds and hundreds of hunting rifles..the sole rifle I've ever seen that would really qualify as burned out was a 60s vintage 22-250 that had seen plenty of prairie dog towns- the first 4" of rifling was just gone. Barrels have come a long way since then and I may never see another one like that.

 

[elkchsr]

Anybody have any thoughts as to weather case design plays a role in barrel life? A good example would be a 243 win compared to a 243 AI. I’ve read that the sharper shoulder angle of the AI case will direct more of the hot gas to the inside of the case neck instead of the throat.