Numerical technique to calc cartridge's barrel 'friendliness', ceribus parabus?

[Dannix]

I think I got down the 'general guidelines' pertaining to barrel life -- Octopus has a great post here. I'm looking for something more concrete than general guidelines though, for, say, comparing wildcats (or tweaking a wildcat's load). How can you tell, just by reading a cartridge's specs, how much of a barrel burner a cartridge design is likely to be? Can you experienced guys just tell, based on experience? If so, what do you look for? Is there a numerical technique to the determine barrel 'friendliness' of a given cartridge design?

Naturally, how one uses are rifle will influence barrel life. I'm talking just cartridge design here though, cerebus paribus (all else being equal e.g. ignoring actual use like rapid fire / heat et al).

I ask because sometimes it seems necking a case down, like the .308 down 0.62mm to 7mm for the 7mm-308 apparently doesn't create barrel life issues, but necking the .284 a smaller 0.5mm down to 6.5mm for the 6.5x284 drops barrel life by a significant margin. I would like to be able to calculate numbers to know if, say, necking the .408 ChevTac down to .375 is a non-issue like the 7mm-08 or a significant issue like the 6.5x284. Or, say, how much less barrel life could one expect when going from 7mm-08 to .260 Remington (6.5-08).


Aspects that would need to be represented a in formula for a numerical comparison (I think I got them all):

• Ratio of Case Shoulder diameter to caliber diameter -- I'm guessing this is what Octopus was really getting at when he said "Big case capacity with smaller diameter bullet"
• Powder weight
• Powder volume
• Powder burn rate
• Pressure
• Velocity
• Bullet weight -- as per Octopus. This one I don't understand. I'll have to re-read Octopus's post to see if he elaborates on this.

The real issue I imagine with coming up with a formula is getting the right ratios down. For example, varying the powder charge may cause a linear influence upon bullet wear, but "Ratio of Case Shoulder diameter to caliber diameter" may be a geometric influence.

Anyway, thoughs on this would be greatly appreciated. My brain is tired.

 

[navyrad8r]

Brian Litz is bsl135 on the forum. this is right up his alley. Sorry to throw you under the bus Brian...BTW Great shooting by you at Perry!!! i enjoyed talking with you at the Palma match.
Cheers,
Doc

 

[blawton]

The difference between a 408 and 375 is gonna average around 500 rounds difference. The 375 should easily get between 1500 and 2000 rounds down the tube before its done. The main reason why round count gets affected so much or so little is the size of the case and the amount of powder you are burning in the first place. Heat is the main enemy of barrel life.

 

[CPorter]

Do a search for barrellifeupdate.xls there is a copy on accurateshooter.com

 

[RonAKA]

The link below provides an empirical formula, which I think is reasonable. It is based on the assumption that a .308 Winchester provides about 3,000 rounds of accuracy, and the variables that change that life from the .308 are powder weight (heat in the boiler room), and bore area (how the heat gets out). For sure velocity has nothing to do with it. It is the area of the barrel right at the cartridge (throat) that burns out, not the muzzle. The bullet is stopped in the area that sees the damage. The throat however sees the heat for the longest period of time.

http://yarchive.net/gun/barrel/barrel_life.html