Hi all, 

I've been shooting with just single based (nitrocellulose) smokeless powders over the years. I don't have any experience with double based (nitrocellulose and nitroglycerin). From a lot of my reading of old (Kelver, Whelan, Sharps, etc...) the authors mention that single-based powders burn 'cooler' than the double-based powders. And the higher burn temperatures in the double-based powders can cause faster erosion of the barrel. 

So my question is: has anyone experienced with some of the modern double-based powders excessive erosion in their single-shot rifles? I don't know if modern powders use less nitroglycerin so perhaps this isn't as much of a problem, but with my original Schuetzen rifles with soft-steel barrels I'm hesitant to try them before asking around. I don't want to trade extra accuracy if barrel life will suffer. 

Just for specifics, I'm using IMR 4227 in 8.15x46R (similar to 32-40) but a lot of the other powders I've read about including Accurate 4100, No. 9, 5744, Alliant 2400, 300MP are all double-based. I'm not having as uniform velocity out of 4227 as I was hoping (standard deviations around 30 fps) so I'm thinking the double-based may have better ignition characteristics and lower standard deviation. 

Thanks for reading!

This is for my Aydt so antique circa 1900 barrel. I’m assuming it’s a softer steel, hence my hesitation to subject it to anything too severe.

I would disagree - double based powders have more energy content per mass so when they burn they add more heat into the volume behind the bullet. So you will get a higher gas temperature behind your bullet when using a double based powder versus a single base, for the same charge weight. 

Now as you point out with the smaller charge for a cast bullet you have a lower pressure and temperature compared to a modern style rifle with jacket bullet, which will minimize propensity for erosion. If you have modern steel as Randy noted your barrel life will probably be very very long. What I don’t know is with original barrels with softer steel if the reduction in barrel life with double based powders is any bit appreciable. Hence my question. 

I forget which book I read but it mentions the pressure/temperature or black powder gases are so much lower than any smokeless that those barrels never wear out, just rust out…with an old antique barrel I’m just trying to find what’s going to keep it in good shape the longest.

Right, so assuming volume is fixed (say in that initial moment before the bullet starts moving) and the number of miles of gas will increase as the powder is burned. Then ideal gas law says as the molecules increase and the temperature increases from the burning the pressure will correspondingly increase. 

Looking at the Vihtavuori reloading manual chapter 3 it states that their single base powders contain about 3700 Joules per gram of energy whereas the double base are 4000. So you will be adding more heat and get a higher temperature when burning the same amount of powder. This website for Swiss powders notes for standard rifle cartridges there is a couple hundred deg C increase in temp when burning their double base powders.
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So I do believe that burning double base powders does cause higher gas temperatures, which are above the melting point of steel for a brief instant, hence there will be increase erosion. How much? That I don’t know - it’s hard to say, so hopefully others can chime in if it is significant or not.

If the bullet were never to move (so a constant volume) then I would say more heat (from double base powders) would lead to an increase in temperature and pressure per the ideal gas law.

When the bullet starts moving that’s when things get a lot more complicated. You can’t just use ideal gas law alone, you have to also consider more thermodynamics and the change in volume as the bullet rides down the barrel. That’s when both the composition of the powder and burning rate begin to matter. 

I’ve run these through an internal ballistics calculator and it shows that you do get higher temperatures behind the bullet with the same charge with double base powders even if you adjust the charge weight so you have the same muzzle velocity. I’d be happy to share more results if you like. 

The most popular commercial code is Quickload
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The one I have is similar and uses the equations in chapters 1-5 in this book:
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They both calculate the motion of the bullet down the barrel and include the chemistry of burning the powder and relevant thermodynamics. They are pretty nifty tools.

You won´t be using the same powder quantity with double-based powder, assuming your goal is the same MV. Assuming identical burn rate and bullet weight, you'll be loading to the same pressure/ temp .So IMO there' no appreciable difference.  Burn rate, regardless of powder composition,  will be more important.

Thanks for the input MartiniBelgian. So I gather then you haven't seen any erosion with double-based powders.

So I ran a comparison case in my internal ballistic calculator, I think this will be interesting. I used a high-power cartridge (7.62x53R) since that is what I had on-hand with the input file. I ran the simulation with a single-based powder and a double-based powder, both with the same burn rate.  The single base powder used 42.5 grain and had an muzzle velocity of 2626 fps.  For the double-based powder simulation I iterated on the charge weight until I got the same muzzle velocity, which was 40.2 grains. The double-based powder has 8% more energy content per mass. See the attached photo for the time curves. 

End result from the simulation, the peak pressure and temperature for the single base powder was 41,300 psia and 3865 deg K (6956 deg F). For the double-based peak pressure and temperature were 40,990 psia and 4125 deg K (7425 deg F). In other words, reducing the charge weight of the double-base powder to match muzzle velocity does bring the peak pressure close to that of the single-based, but the peak temperature is still 400 deg F hotter. 

I also ran a couple more simulations with even further reduction in double-based powder charge. The peak pressure reduced but peak temperature still remained higher than the single-based. So I am fairly sure no matter what the double-based always burns hotter, which is why I'm trying to understand if this is problematic if one has a softer-steel barrel. I'll redo the simulations later with more appropriate single-shot cartridges, but I'm expecting the same result.