A picture, a thousands words . . .





Flake









Ball
























Extruded














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So other than the process to make them which is the best for reloading and/or using? It does seem like from the pics that Extruded is the most consistence.

The spherical meter the most consistently. But the real test is how they shoot. There are examples of each type that produce the best accuracy (at least in pistols, since that is the area I'm most familiar with) in some calibers.

Some folks distinguish between ball and spherical. Winchester calls many of their powders 'ball', but they look more like irregular flattened flakes than ball-like objects. Examples include 231 and 572. Spherical is the term that best describes the true ball-like round pellets.

There is also one donut shaped powder... IMO, Trail Boss is the powder that should have been called unique...

not my pic:

I'll see if I can get a pic of VV N32C "Tin Star".



I think it's a really fluffy flake.

Possibly a million words...
Been around for a while.

http://www.ilrc.ucf.edu/powders/search.php?resultPage=1&resultPageSize=50

That "best" question is pretty much philosophical, verging on religious!  

The process that is used to make each powder has a lot to do with the powder's characteristic burn rate and energy content, but it also contributes to things like loading density, ease of metering, and issues with filling cases.  Consistency of each grain's size is not nearly as important as other factors.  For example, with ball/spherical powders, there will be a variety of different sized grains, but any powder throw will have an essentially identical mix of the different sizes, which gives each powder throw essentially identical burn characteristics.  And it's important to understand that smokeless powder burns ONLY on its surface, so the grain structure (like the donut-shaped grains) has a very strong affect on burn rate.

The smokeless powder used in 16" naval rifles (the big guns on battleships) had granules of about the same size as a loaded .45ACP round, with 7 lengthwise holes in each grain - these guys burned really slowly, but they had a HUGE barrel length in which to burn.  And that powder was used to throw a projectile the size of a Volkswagen to a range of about 25 miles...  So smokeless powder is kind of a complex subject, even for a small time handloader.

"Extruded" can also have passages running the length of the extrusion to alter surface area.

"Ball" is flatt4ened to make fine adjustments in surface area to volume ration that affect burn rate.

True spheres have a smaller surface to volume ratio.

Flakes have a huge surface to volume ratio.

Volume is often used instead of actual weight.

And NOT 'bulk' volume.

Granule volume.

Also remember that the lengths of the extruded powers vary greatly. Varget is a mid-length where IMR 4198 is very long.

Thanks for the link, great info and pics

No problem.

The last two pictures in the "ball" category are generally referred to as "flattened spherical" powders as they are no longer strictly ball powders.

Flattening them increases the surface area relative to their weight, and effectively increases the burn rate.

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Ball powders became very popular in the 1960s as they could be manufactured from recycled cannon powders, used in both artillery and naval guns.   They could also be made very quickly - on the order of 2 days compared to about 8 weeks for an extruded powder.  In addition, different lots of colloidal ball powder with different properties can be mixed by the ballistician to create powders with very specific burn traits.

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Size, shape, the size and number of longitudinal holes in the grain and retardant coatings on the grain all can be used to manage the burn rate and the pressure curve.

For example, an extruded cylindrical powder grain will start with maximum surface area and that area that is actively combusting will get smaller as the cylinder burns from the outside in.  However with a longitudinal hole in the middle, it will have a slight increase in initial surface are, and the hole will cause it to also burn from the inside out - increasing the interior surface that is burning to partially offset the decrease in the exterior surface that is burning.  

Loaded into case before necking to final size.

Rather than screening the "Ball Powder" to achieve uniform pieces, the still moist and flexible pieces are run between rollers to flatten the pieces to the same maximum thickness. The fact that a piece may look almost like a pancake doesn't matter since burning is a surface phenomenon. If each piece is the same thickness, each one will burn through from side to side in the same time.
This is called "Rolled Ball Powder".

Excellent pictures of Naval Gun propellant. Only large guns can use such large propellant granules. They have two advantages unavailable to "smaller" guns.
  1) The larger pieces of extruded propellant can be made with seven perforations through their centers. Each perforation will burn larger with time while the outside of the granule decreases in size with time. This results in 7 increases in burning surface with only one decrease in burning surface. The net result is a progressive rate of gas production.
  2) While "normal" calibers use double or single base propellant (Nitrocellulose and Nitroglycerine or Nitrocellulose only formulations), the large guns can use triple base propellant (NC, NG, and Nitroguanidine). Triple base propellant has a burning rate too slow for smaller calibers; however,for the big guns, it is great.

Large guns have a 'pre-stress' built into their construction.

By heating the outer portion at the breech end and shrinking the inner portion and then forcing them together a huge mechanical stress is left on the inner layers.

Those 'steps' you see on a larger gun barrel are not just for weight savings.

Until pressure inside the barrel exceeds this pre-load there is no actual outward (hoop) stress on the barrel material that would cause failure.

What did you say that 'chamber pressure' is?

Thats really nice powder.  Meters great and very accurate.  Too bad its really hard to get around here.  And yes, very round, and messy if you spill it due to being very fine and almost perfectly round.

VV N32C "Tin Star"









Red Dot









IMR4064

Is that 4064 hollow? I'm off to look at powder now...

Yes, that powder is "hollow."  There's a lengthwise hole through each grain.  That hole increases the surface area of each grain, and since smokeless powder burns only on the surface, while the outside gets smaller, the inside will get bigger, for a more consistent burn rate.

Very interesting. I have never loaded 4064 but I do load Varget, 8208, 4895 and 4198. I had never looked at them closely enough to see if they have that feature.

The IMR-4064 picture sure looks like at least some grains are hollow, though not to the extent that Tin Star is.  That may just be shadows cast by irregularities at the cut ends of the grains.