Reloading conundrum

oremike · Apr 23, 2024

It's a given that different powders have different burn rates and that can equate to time. By that I mean to generate the same pressure behind the same weight of bullet a slower powder will burn longer than a faster powder. This will cause a different rate of acceleration and it is my thought that once the powder quits burning the bullet can go no faster. Everyone knows that a given load will shoot faster in a longer barrel as compared to a shorter one but is there a way to determine barrel dwell time to optimize the powder to the load?

P7M13 · Apr 23, 2024

Gordons Reloading Tool -- GRT

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Pepe-lepew · Apr 23, 2024

oremike said:
It's a given that different powders have different burn rates and that can equate to time. By that I mean to generate the same pressure behind the same weight of bullet a slower powder will burn longer than a faster powder. This will cause a different rate of acceleration and it is my thought that once the powder quits burning the bullet can go no faster. Everyone knows that a given load will shoot faster in a longer barrel as compared to a shorter one but is there a way to determine barrel dwell time to optimize the powder to the load?

What is it we are trying to optimize?

The area under the pressure curve tells a lot. If you want velocity, you want a pressure curve that reaches max instantly and stays at max until the bullet leaves the barrel. However, it does not work that way. Slower powders are slow to rise and may still be burning when the bullet leaves the barrel. They can increase velocity but are limited by many things such as case capacity and barrel length. Faster powders come into play to deal with those limitations. You will see trends in velocity as the powder burn rate changes for a given case, bullet and barrel.

I like to optimize time and money. I see what is working well for others in a similar application and mimic what they are using.

Koda · Apr 23, 2024

oremike said:
but is there a way to determine barrel dwell time to optimize the powder to the load?

A ballistic calculator will give the time of flight to a distance, maybe you could subtract the barrel length from that but not certain how accurate that would be from ignition to muzzle velocity.
The only other way I can think of is to use a high speed video camera to film super slow motion and time the frame rates from the trigger pull till you see the bullet leave the bore.

BigGame · Apr 23, 2024

Like GRT, QuickLoad software also estimates barrel time.

gmerkt · Apr 23, 2024

I'm thinking that how much pressure builds during dwell time is an important thing to know. I agree that one of those computer simulation programs would be the way to go. Modern and scientific.

Maybe barrel dwell time is determined by other factors, not the other way around.

"Optimize the powder to the load." In terms of velocity? Or in terms of economy? When I've looked at load recipes that show them together in comparison, I have a habit of seeing how much velocity is obtained in relation to the weight of the charge. An optimized load in that case would be the highest velocity for the least amount of powder expended.

DuPont (and later, for a time, IMR) used to publish a reloading handbook. It was pretty neat, they had CF rifle loads for all popular calibers using every powder in their line. It was really easy to compare charges and velocities for the otherwise same components. You could see which cartridges "liked" slower powders, and which liked faster ones, and those that were more versatile across a wider range of propellants. But of course, that was just for their own products. Which are almost non-obtainable now.

P7M13 · Apr 24, 2024

oremike said:
It's a given that different powders have different burn rates and that can equate to time. By that I mean to generate the same pressure behind the same weight of bullet a slower powder will burn longer than a faster powder. This will cause a different rate of acceleration and it is my thought that once the powder quits burning the bullet can go no faster. Everyone knows that a given load will shoot faster in a longer barrel as compared to a shorter one but is there a way to determine barrel dwell time to optimize the powder to the load?

I have never used Quick Load, and have not used GRT enough to see its calculus nuances.
However, the burn characteristics, and thus pressure curve, of many powders will change with increased powder amount. It's not a simple, linear relationship between powder amount and pressure. Many powders will burn inefficiently (dirty) at lower pressures, but will give a lot more oomph (and burn much cleaner) when they are loaded to their ideal pressure curve.
Just like the burning of natural gas is a multi-part chemical reaction (CH4 + O2 -->> formaldehyde + O2 -->> CO2 + H2O), the burning of smokeless powder likely has more than one step in the oxidation reaction.
But, the above is s not a statement of "more = better". Some powders will react violently, resulting in a kaboom, when the pressure causes the burn rate to accelerated to that of a much faster powder.

oremike · Apr 24, 2024

What got me thinking about this was loading and shooting 357 Sig. I'd made a load with a 125gr bullet and AA#9 powder that I got a lot of muzzle flash out of my 3"" Shield but no so much out of my 4" Sig.

Pepe-lepew · Apr 24, 2024

Some things to keep in mind, chemical reactions never occur as predicted. Computer models are only as good as they are built and are never perfect. An example is crimp or bullet hold, it will change the pressure curve. It is hard to add to a model and changes the reaction rate.