Barrel life vs. Wind Drift

[atek3]

It seems there is a great inverse correlation between Barrel life and Wind Drift numbers. 7RM with VLD's, 6.5x284 and 6mmXC throwing the 115gr DTAC all have great wind drift numbers, but very poor barrel life. 223 and 308 have relatively poor wind drift but good barrel life. The high BC bullets favored by long range shooters tend to have long bearing surfaces that are harder on barrels, and the relationship between muzzle velocity and wind drift means that long range shooters tend to drive the bullets as fast can while still maintaining accuracy and safety. Are there any cartridge/bullet combos that defy this relationship, ie good barrel life and good drift numbers?

atek3

 

[Jim Watson]

I am confident that if there were a way to shoot closer to the wind without burning barrels, that somebody would have found it and made a lot of money off of it.

 

[Gewehr98]

It's not the bullets that are particularly hard on the barrels.

It is, however, the amount of powder one burns through the barrel throat that leads to short barrel life.

Heavyweight VLD .223 Remington loads, say those 80gr Berger VLD loads folks like for NRA High Power, aren't so tough on barrels compared to that same bullet loaded into a .22-250 or .220 Swift, with a bunch more powder behind it. That extra powder's gotta go somewhere when it's lit off, and it does, continuing the burning process down the throat and the bore. Some would argue that unignited powder grains bead blast the throat before igniting further down the barrel. Result - eroded barrel throats, and lost accuracy after X amount of rounds fired.

Bottleneck rounds with small diameter necks, like the 6.5x284 and 7mm Remington Ultra Mag, concentrate their erosive effects compared to rounds like the .416 Rigby or .458 Winchester Magnum. P.O. Ackley described the former as "overbore", and noted a diminished return of velocity improvement with each extra grain of powder added once a certain "efficiency" was met. In other words, extra powder may mean more velocity in an overbore case, but the velocity increase won't be as dramatic as it would be with a more efficient, less overbore case. The difference between a 6.5-06 and 6.5-06 Ackley Improved or 6.5 Gibbs is an example of that. The improved versions do offer an increase in velocity, but not as much as the extra grains of powder would make one think.

Another way to look at barrel life is as a simple function of powder burned through it.

One would never think a .22 Long Rifle barrel would be burned out and have a chewed-up throat after a thousand or so rounds. There's maybe about 5-10 grains of powder per each round fired, right? Just getting to a pound of powder is going to take roughly 700 rounds at the higher figure.

Now take .30-378 Weatherby Magnum, with well over 100 grains of powder in each round. That beast is burning up to 122 grains of powder behind a .30 caliber 180gr bullet. That's 57 rounds per pound of powder, roughly 12 times as much powder per round as the little .22 Long Rifle.

 

[RecoilRob]

Just weighed a Remington Thunderbolt's powder....1.7gr. Doubt any .22 has more than 2gr but your point is correct and well taken.

I have had a .22 barrel hot to the touch but it took a couple hundred rounds as fast as I could fire and change 30rd mags. The AR-15 gets as hot or hotter with a single 20rd mag. Heat causes erosion and burning powder makes heat.

And, trying to funnel a bunch of powder very quickly through a tiny hole surely causes some wear ala sandblasting. Which brings up the case volume/bore relationships in US military ammo. No crazy overbore ammo makes it into the inventory because it is harder on throat life.

 

[js2013]

As mentioned above overbore and heat (rapid fire) have the biggest influence on throat wear. However case dimensions will play a lesser but still significant role. For example a 243 will wear out a throat faster than a 244/6mm AI, even though the AI uses more powder and can push a bullet faster.

 

[USSR]

How 'bout that, an inverse relationship of velocity and barrel life? Seriously, the best you can do is use the most efficient cartridge for the velocity you want to attain. Example: I load my .30-06 with 60-61gr if RL-22 to drive a 190SMK at 2900fps; with a .300WM it may take 71-72gr of the same powder to drive the 190SMK at the very same 2900fps. Using less powder in a smaller case to reach the same velocity as a larger case with more powder will improve barrel life while giving you the same elevation and wind drift #'s.

Don

 

[atek3]

I wonder what the barrel life of the very very efficient 6.5 grendel will be?

atek3

 

[JohnKSa]

Some believe that boat-tail bullets increase the rate of bore wear. If that's the case (and I've seen it reported by some pretty experienced shooters) then there's sort of a triple threat in terms of factors that increase barrel wear but which improve wind-drift.

high velocity
boat-tail design
longer bearing surface

 

[Coronach]

An aside, re: bearing surface

Query: what is it about greater bearing surface that allows bullets to better withstand the effects of wind? Is it merely that longer bullet lengths are associated with greater BC, or is it something else?

Mike

 

[JohnKSa]

Very roughly speaking, it's length vs weight that makes the difference. You're right, it's not necessary to have long bearing surfaces to achieve good sectional density/BC, but that's the way most bullet makers do it.

While I'm typing this, I'm looking at a fired 20mm bullet that has a very short bearing surface but is a relatively long bullet. The bearing surface is a narrow band around the diameter of the bullet right at the point where bullet would normally meet the case. It has taken a good rifling imprint, but the rest of the bullet is unmarked. The bullet looks like some sort of an AP round (it hasn't deformed a whit even though some deep scratch marks on the nose and the rifling marks clearly indicate it has been fired) so in this case, I suspect the bearing surface was implemented this way to prevent the hard material of the AP round from prematurely wearing the barrel rifling.

 

[Jim Watson]

Long bearing surface works AGAINST high BC. Look at a VLD. It has a lot of nose and boattail for good form factor and high BC but such a short bearing surface that it is usually seated so as to set the ogive into the rifling to improve alignment with the barrel at launch. Conventional bullets have longer bearing surface and are less critical in seating, but have lower BC for the same SD.
Then there was the Century XIX Krnka-Hebler bullet, completely torpedo shaped, tubular, and sealed by a sabot. Inaccurate but claimed range of 8000 yards.

 

[carebear]

Then there was the Century XIX Krnka-Hebler bullet, completely torpedo shaped, tubular, and sealed by a sabot. Inaccurate but claimed range of 8000 yards.

That'd be for.... what? Nebraska prairie dogs? From Wisconsin?

Tubular meaning "ring air foil" hollow all the way through?