Powder Shapes and Properties

[DMW1116]

Just looking over the powders I’ve used since I started reloading in May of last year. Most are ball powders like LEVERevolution and H335. However one stands out as the most reliable I’ve tried for accuracy and it’s a stick powder. What does shape have to do with properties of the powder? Are stick powders inherently more accurate? Do ball powders generally give higher velocities? If ball powders are just as accurate, why are stick powders still around?

To my knowledge I’ve not used a flake powder, though some of the ball powders are flattened a little to keep them from just rolling around and can therefore look like tiny flake powders.

 

[AJC1]

You may want to also observe in most cases extruded powders are single base and more temperature stable than their contemporaries. Shape is just one factor but generally means it shares other important attributes.

 

[DMW1116]

By temperature stable you mean they ignite reliably when cold or don’t ignite too easily when hot? Or do they give consistent velocity over a wide range of temperature?

 

[Demi-human]

I know that balls will bounce farther than sticks will…

 

[mcb]

The grain shape of the powder changes the effective burn rate of the powder (along with the ingredients in the powder) by how the available surface area changes as the grain burns. Only the outside surface of powder grain burns and as it burns the grains surface area available to burn changes. Spherical grain shape will drop off surface area the fastest than stick powder slightly slower a flat flake even slower to loose surface area. You don't see it often in small arms but with the bigger guns you will even see perforated stick powders.

https://www.vihtavuori.com/tech-blog-powder-grain-shapes/

Nice overview

http://www.prodas.com/XQ/ASP/P.603/QX/Documents/Propellant Geometry Type Descriptions.pdf

This paper has a nice graph showing how the surface area changes as the various powder grains burn.

 

[Ru4real]

Stick powders rely on (1) their shape and (2) burn inhibitors (chemicals) to control burn rate. Thus they are typically more consistent for similar velocities at a wider range of ambient temperatures. Mostly, but not always.

Conversely, most ball and flake powders only rely on burn inhibitors (chemicals) to control burn rate. You probably know ambient temperatures have a big impact on chemical reaction rates, thus smaller grain powders, with more chemicals, tend to be more variable. Mostly, but not always.

Stick powder shape controls burn rate in that the stick burns from the outside inward and the burning surface tends to shield the inside as it burns inward. Think charcoal briquette.

 

[Ru4real]

I see @mcb beat me to it.

 

[Jim Watson]

This paper has a nice graph showing how the surface area changes as the various powder grains burn.

Ah HA. I thought IMR powders were perforated and this says so for sure.
There was even perforated black powder developed with the cannons by Rodman.

Kind of confusing calling extruded powders "cord" type when the common usage is for Cordite which is actually loaded in long strands instead of being cut into short granules.

 

[mcb]

Ah HA. I thought IMR powders were perforated and this says so for sure.
There was even perforated black powder developed with the cannons by Rodman.

Kind of confusing calling extruded powders "cord" type when the common usage is for Cordite which is actually loaded in long strands instead of being cut into short granules.

I can remember using 3031 to load light bullet in 270 win with my father for groundhog hunting and seeing the perforated stick.

Trail-b0ss is the first perforated flake I had ever used. I suspect that is less about changing the burn rate in that case and more about decreasing the bulk density. Not doubt it effect burn rate to some extent too.

 

[DMW1116]

Ok that all makes sense. H335 is one of my favorites right now but I have not used it for an accuracy load and I don’t have much left. I’ve used it for FMJ loads in 30-30 and 223. It seems to have good velocity in those.

IMR 4064 is my favorite for my most accurate loads, but again I haven’t found any lately. It has produced sub 1” groups at 100 yards in 3 loads and 2 calibers. I know I’m giving up some velocity, but I’m ok with that as long as it shoots like these loads do.

 

[AJC1]

By temperature stable you mean they ignite reliably when cold or don’t ignite too easily when hot? Or do they give consistent velocity over a wide range of temperature?

Yes

 

[mdi]

The grain shape of the powder changes the effective burn rate of the powder (along with the ingredients in the powder) by how the available surface area changes as the grain burns. Only the outside surface of powder grain burns and as it burns the grains surface area available to burn changes. Spherical grain shape will drop off surface area the fastest than stick powder slightly slower a flat flake even slower to loose surface area. You don't see it often in small arms but with the bigger guns you will even see perforated stick powders.

https://www.vihtavuori.com/tech-blog-powder-grain-shapes/

Nice overview

http://www.prodas.com/XQ/ASP/P.603/QX/Documents/Propellant Geometry Type Descriptions.pdf

This paper has a nice graph showing how the surface area changes as the various powder grains burn.

Yeah, what he said!

 

[Walkalong]

Stick powder has always ruled at long distance.

 

[Jim Watson]

Yes. I really wanted to like AA2520 for F class, it meters so well as to eliminate the need for a trickler or dispenser. But any extruded powder I tried was at least a little more accurate. On to Varget.

 

[twarr1]

Spherical powders are cheaper, easier and safer to manufacture. A lot of extruded powders (H4198, H322, Varget, etc) are single base and don't contain nitroglycerin.
All double base propellants contain nitro. There are triple base powders as well, but none available to reloaders.

 

[ArchAngelCD]

Yes. I really wanted to like AA2520 for F class, it meters so well as to eliminate the need for a trickler or dispenser. But any extruded powder I tried was at least a little more accurate. On to Varget.

AA2520 is the ball powder version of AA2495. AA2495 is formulated to mimic IMR4895 so you are in good company with AA2495 if you want to stick with Accurate powders.