Erosive Effects of Different Powders

[South Pender]

I've been doing some load development work, with QuickLoad by my side, for my 6.5x55 SE. I've found that the powders that offer the best velocity/pressure combinations, particularly with heavier bullets, run from some Alliant powders (Re22, Re23, Re25) to IMR 7828, and to Vihtavuori N560. However, these powders vary greatly in their flame temperature (as shown in QuickLoad), with Re25, for example, showing a flame temperature of 3810 to Vihtavuori N560 at 4020. According to the barrel life calculator, this difference will result in quite different barrel life, with N560 showing much lower barrel life than Re25 (with powder charges that produce the same velocity/pressure)--about 80% for N560 when compared to Re25.

Is this differential real? Or merely the result of a theoretical algorithmic model? Do you guys take the issue of flame temperature into account in your handloading?

 

[deadidarren]

I do it's the main reason I steer clear of H4831 and where I can I stay with H4350 and H1000

 

[Hudge76]

Did you watch the recent Winning in the Wind video on this topic?

 

[ShaunBrady]

Those are not flame temperatures, they're the heating value of a given amount of powder.

The flame temperature will depend more on the pressure you load to than the powder used.

Reloder 22, 23, and 25, as well as IMR 7828 are single base powders. N560 is double base. Double base powders contain nitroglycerin which brings more oxygen to the combustion process. It's the difference in combustion products that affects the barrel life estimate in calculators that include that effect.

 

[South Pender]

Those are not flame temperatures, they're the heating value of a given amount of powder.

The flame temperature will depend more on the pressure you load to than the powder used.

Reloder 22, 23, and 25, as well as IMR 7828 are single base powders. N560 is double base. Double base powders contain nitroglycerin which brings more oxygen to the combustion process. It's the difference in combustion products that affects the barrel life estimate in calculators that include that effect.

It was my impression that the Alliant Reloder series (22, 23, 25, and others) are double-base powders. I've read that more than once.

 

[FeMan]

In my experience, there does seem to be a real correlation between the Ba and barrel life. Another factor I believe contributes to throat erosion is how fast the powder is consumed in the barrel. All things being equal, a powder that has 100% burn in 50% of the barrel seems like it would flame crack the barrel faster than one of equal Ba and pressure curve that is 100% or less at the muzzle.

 

[South Pender]

In my experience, there does seem to be a real correlation between the Ba and barrel life. Another factor I believe contributes to throat erosion is how fast the powder is consumed in the barrel. All things being equal, a powder that has 100% burn in 50% of the barrel seems like it would flame crack the barrel faster than one of equal Ba and pressure curve that is 100% or less at the muzzle.

Doesn't Ba refer to the burning rate, rather than what QuickLoad calls the "heat of explosion," what I earlier termed flame temperature? As I understand it, Ba follows pretty closely the usual burn rate charts, but that shouldn't affect throat erosion, should it?

 

[FeMan]

I miss poke earlier. I was typing way past my bedtime!

I meant to say, "...there does seem to be a real correlation between the Heat of Explosion and barrel life."

The Heat of Explosion refers to the amount of energy that is released when the powder burns. The units are energy/weight. I think that relates more to flame temperature although it isn't actually a temperature.

Sorry for the confusion.

 

[K22]

In my opinion, you shouldn't be worried about this issue. Use the powder that gives you the best performance in your rifle to give you the most enjoyment.

If you shoot a lot, like I use to before this component mess, then barrels are consumables. It's like replacing tires on your vehicle. Don't limit your enjoyment trying to extend the life of a rifle barrel. Your goals should be to wear out the barrel before you pass to the "big range in the sky". "He who shoots the most wins in the end!"

If barrel wear is a concern, then choose cartridges like the 308 and 223 and avoid heavily overbore cartridges like the 6mm-284. However, those who shoot those overbore cartridges do so for the performance aspect and therefore accept the tradeoff of shorter barrel life for the extra performance that these overbore cartridges offer. I think the cartridge you listed is like the 308 and 223, relative to barrel wear, i.e., favorable bullet diameter to powder ratio.

Also, if you can avoid it, don't shoot rapid fire strings overheating the barrel which I believe does more harm than the type of powder you are using.

 

[South Pender]

I miss poke earlier. I was typing way past my bedtime!

I meant to say, "...there does seem to be a real correlation between the Heat of Explosion and barrel life."

The Heat of Explosion refers to the amount of energy that is released when the powder burns. The units are energy/weight. I think that relates more to flame temperature although it isn't actually a temperature.

Sorry for the confusion.

Yes, thanks for that FeMan. "Heat of Explosion" describes the phenomenon much better then "flame temperature."

 

[South Pender]

In my opinion, you shouldn't be worried about this issue. Use the powder that gives you the best performance in your rifle to give you the most enjoyment.

If you shoot a lot, like I use to before this component mess, then barrels are consumables. It's like replacing tires on your vehicle. Don't limit your enjoyment trying to extend the life of a rifle barrel. Your goals should be to wear out the barrel before you pass to the "big range in the sky". "He who shoots the most wins in the end!"

If barrel wear is a concern, then choose cartridges like the 308 and 223 and avoid heavily overbore cartridges like the 6mm-284. However, those who shoot those overbore cartridges do so for the performance aspect and therefore accept the tradeoff of shorter barrel life for the extra performance that these overbore cartridges offer. I think the cartridge you listed is like the 308 and 223, relative to barrel wear, i.e., favorable bullet diameter to powder ratio.

Also, if you can avoid it, don't shoot rapid fire strings overheating the barrel which I believe does more harm than the type of powder you are using.

Good advice, K22. The time between shots is a key variable in the Accurate Shooter barrel life calculator: (http://bulletin.accurateshooter.com/2008/10/spreadsheet-formula-calculates-useful-barrel-life/).

I ran some data for a 6.5x55 with a full charge of an appropriate powder, and the predicted barrel life went from 424 shots with a 10-second interval between shots to 1685 with a 1-minute interval between shots. That much difference seems a little hard to believe, but that's what the program spat out.

 

[Sechrist2015]

All I know about erosive effects, is that varget is terrible on the barrel of a 30BR gun built for lead. It makes the barrel run super hot in match strings, and the throats will start to show fire cracking by 1000-1200rds on some barrels.

So we run VV and call it a day. Better barrel life and they don't get hotter than ©$&@.

 

[K22]

Good advice, K22. The time between shots is a key variable in the Accurate Shooter barrel life calculator: (http://bulletin.accurateshooter.com/2008/10/spreadsheet-formula-calculates-useful-barrel-life/).

I ran some data for a 6.5x55 with a full charge of an appropriate powder, and the predicted barrel life went from 424 shots with a 10-second interval between shots to 1685 with a 1-minute interval between shots. That much difference seems a little hard to believe, but that's what the program spat out.

I have a real-world example. The 243 Win has a reputation for short barrel life. True it is somewhat of an overbore cartridge, but I got over 3,000 rounds through my Rem 700 until groups started to open up a bit from about 1/2 moa to about 1 1/4 moa. Still with hunting capability limits.

The key I believe was that I never shot hot barrel strings. Oh, a few times I may have shot two in row while hunting but it was rare. My range practice was based on cold / cool barrel shots under the premise that the cold barrel shot is the "money" shot. So, it would normally take me about an hour to shoot 10 rounds out of one rifle.

 

[South Pender]

All I know about erosive effects, is that varget is terrible on the barrel of a 30BR gun built for lead. It makes the barrel run super hot in match strings, and the throats will start to show fire cracking by 1000-1200rds on some barrels.

So we run VV and call it a day. Better barrel life and they don't get hotter than ©$&@.

Yes, according to QL, Varget has a Heat of Explosion of 4050 kJ/kg--among the hottest of all the powders.