"all things equal" barrel life question

[SquarePizza]

I read all the time that speed kills. But let us say that you have a 243, 260 rem, and a 308 win and fire appropriately heavy projectiles so that they are all running 2750fps.

Given an equal velocity, why would the 6mm still be assumed to wear out quicker?

 

[RobertB]

I would believe it to be a yes, If I'm not mistaken its pressure that kills the bbl. More powder down a smaller hole. You should still have more powder in small calibers igniting about the same amount of powder whether its a small bullet or heavy. You would have to use less powder in smaller bore rifles to get the bbl life, then its no point to choose that cartridge.

 

[tnichols]

Same amount of pressure/heat, but concentrated into a smaller/tighter area (the throat of the chamber). Just my opinion, I'm wrong a lot.

 

[damoncali]

Barrels erode for a lot of reasons. One of those is that the heat from the burning propellant melts the surface of the bore - the temperature of the gasses is higher than the melting point of steel for a small fraction of a second. The more heat per square inch of bore surface, the greater the effect.

But this is not a the only cause of erosion, so it's not as simple as grains of powder per inch of bore circumference.

 

[SquarePizza]

I kinda figured that was the a factor but I wanted to ask anyways. =)

 

[40xs]

Did you ever do any welding/burning with a torch? cutting metal with a torch requires that you adjust the flame down to a more narrow pinpoint flame verses a larger slower flowing gas and oxygen mix. A similar concept and one that explains why the throat always goes before anything else.

 

[Ring]

more powder down a smaller hole, and PSI of your load....

IE: running "factory" loads in a 243 VS 260, the 260 will last longer, running "light" loads at a lower chamber PSI, the 243 will last longer..

IE the 6.5 SAUM from GAP...
200fps faster then a 6.5-284, but since its running at a lower PSI, the barrel life is 2 to 3x more

 

[HodgdonExtreme]

A question that dovetails nicely into this thread:

What is gentler on a barrel:

A 6x47 running 105 berger @ 3150fps using 39.5gr H4350

Or, a 243 running 105 berger @ 3150 using 43gr H4350?

 

[wigwamitus]

When I bought my Savage 110BA .338LM ... I believed the .300WM would cut my factory ammo costs in half ... but also cut my barrel life in half ... this based solely on internet reading ... hence I got the .338LM ... I'm still trying to get reloading going for the .338LM ... my current ammo prices are $3/rd for 250SMK or 300SMK ... HSM or $4/rd for Lapua brass version ... I believe Lapua brass to be good for about 11 reloads and non-Lapua (good) brass to be good for about 4 reloads, based on talking to people who have reloaded both for .338LM. So I think with reloading, I can get cost down to between $1.50 and $2.00 per round (not counting reloading gear which I have already acquired). But it remains to be seen whether the barrel life of the .338LM will push up into the 4,000 to 5,000 round level for me. I do not want to push the edge of the envelop of speed, I just want to get sub-MOA out as far as I can, hopefully 1-mile to 2k. That is my "mount everest" but I expect it to take another 1-2 years to get there ... and I'm fine with that.

 

[jake6547]

If I were to guess the 6x47 seems like a more efficient cartridge because its reaching the same velocity with less powder so I chose that one to be gentler out of the two. Judging by your name im thinking that was a rhetorical question and Im about to find out the answer. ??

A question that dovetails nicely into this thread:

What is gentler on a barrel:

A 6x47 running 105 berger @ 3150fps using 39.5gr H4350

Or, a 243 running 105 berger @ 3150 using 43gr H4350?

 

[HodgdonExtreme]

If I were to guess the 6x47 seems like a more efficient cartridge because its reaching the same velocity with less powder so I chose that one to be gentler out of the two. Judging by your name im thinking that was a rhetorical question and Im about to find out the answer. ??

It wasn't a quiz, it was a real question asked in earnest.

I don't know the answer. On one hand you are creating more pressure with less heat, and the other is less pressure with more heat.

We know both heat and pressure eat throats. Which is the prevailing one?

 

[damoncali]

I've read a good bit about military erosion tests, and I can honestly say I have no idea. It gets so complicated so quickly... Unfortunately most of the scientific effort that I have seen has gone into figuring out ways to reduce erosion, not ways to predict it. You get the standard "increases with pressure, velocity, charge weight, flame temperature, etc", and then lots of discussion about bore coatings and propellant additives. Very little about rates for different bore sizes, shoulder configurations, bullet weights, and the sorts of things that we care about.

 

[jake6547]

Another good comparison is the 260 Ackley improved compared to the 6.5-284,

-6.5-284 140 gr projectile 2950 fps barrel life 900-1000 rounds

-260 Ackley 140 gr projectile 2950 fps barrel life I have heard is around 2000?
-So very similar in everyway except the 260 AI is a more efficient case design and gets to 2950fps with roughly 3 grains less powder which equates to less barrel erosion? keep in mind im just theorizing here.

It wasn't a quiz, it was a real question asked in earnest.

I don't know the answer. On one hand you are creating more pressure with less heat, and the other is less pressure with more heat.

We know both heat and pressure eat throats. Which is the prevailing one?

 

[HodgdonExtreme]

An interesting point I don't see made often regarding barrel wear and throat erosion is how far down the barrel it extends.

When we discuss erosion, I think it usually sounds as if the affected area is mainly relegated to just the throat, but in fact, it extends a LONG ways down the barrel.

For example, I recently scoped out:

~800 round 6XC
has had 500 fireforming loads with the Berger at 2950, and about 300 full power loads at 3140fps.
Shot at matches and for some recreational target shooting
Melonited Benchmark barrel
Shows some definitive erosion in the throat and heat cracking extending 6" or so down the bore. Not in bad shape, but certainly shows as USED.

~2000 round 284Win
loaded with 175smk at 2825fps
Shot mostly at matches and some target shooting
Krieger 4 groove barrel
Shows *well* used but not trashed, small chunk out one of the lands just ahead of the leade. Heat checking extends 6-8" down the bore

~1800 round 260
run with the 142smk at 2830fps
mainly been used for match shooting and spirited target shooting. Not babied
Bartlein 5R
Shows the worst wear of the three barrels. Throat is eroded, significant heat checking for 6-8". Heat cracking/checking is present all the way to 15" or so down the bore. Doesn't appear "trashed" but looks like it's well past 1/2 life.

Anyway, the point I'm making is the erosion isn't *primarily* focused right on the throat. Yes, the throat is the worst, but it's not as if the rest of the barrel isn't also heavily affected. It is.

 

[Fred_C_Dobbs]

Excel Formula Predicts Useful Barrel Life

 

[Frank Green]

smaller the bore and same case capacity = less barrel life

.243win., .260 Rem. and .308win. all basically the same case capacity.

Other factors....

What type of powder are you loading? Double based powders will burn the barrels faster. No way around it.

Neck length of the case/shoulder angle etc....have an effect as well. One reason I don't like .243win. it notorious for frying throats.

Also as HodgdonExtreme said the wear isn't confined to the throat it will extend down the barrel farther than what most think it does. That's why I'm against setting a barrel back. So you cut an 1" off the breech end and rechamber and yes you will get into nicer rifling but the wear is there already. You are not going to get the same barrel life like you did when the barrel was new. Also if you have to pay a gunsmith to set the barrel back and he charges you another $200-$300 are you getting your money's worth out of setting the barrel back? To me no. If you can do your own work than all your out is your time (my time is precious to me so I again I won't waste my time doing it).

Later, Frank
Bartlein Barrels