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Powder Sifters (aka propellant grain uniformers)
copyright 2017 - Stephen Redgwell

Disclaimer: For information only. Do not attempt anything described in this article yourself.



The federal government, two chemical companies, and three universities are working on an improved system of processing low explosive propellants. These propellants include the commercial brands found on reloader’s benches around the world. The main thrust of this work is to stabilize the burn rates of small arms propellants, thereby producing absolutely uniform velocities.

Deemed "Propellant Stabilization Screening" or PSS for short, scientists are applying an old fashioned idea, long used in household kitchens: Sifting flour, prior to baking, to improve the result.

How does it work?

Employing PSS ensures grain uniformity which stabilizes burn rate and combustion chemistry. Several independent university and military studies conducted since WWII have shown accuracy of SAA (small arms ammunition) can be improved by screening propellants.

The weather, or where you are on the earth, have nothing to do with the result because it is based on grain stabilization technology. This chemistry is unaffected by temperature, altitude, or relative humidity.

Scientists have known for years that sifting works. And it works well, regardless of propellant type – single, double or triple base. But manufacturing improved powders was dangerous. Until now, obtaining homogeneous propellant shape was impossible. So how do companies safely sift powder in the factory? The method may be secret, but here’s what we do know.

There are presently three commercial sifters being tested for spherical, extruded and flake propellants. A home version is also in the works.



How does this apply to me?

Simple. Home sifting may be added to the arsenal of precision reloading equipment on your bench. While it will be most popular with competition shooters, hunters will find it invaluable too. It will take time for all propellant manufacturers to start using PSS. In the meantime, reloaders will be able to use certified sifting technology to uniform any powder on the market, at home.

You won't have to figure this out, but here is a peek at part of the work to date. It is a burn improvement formula (BIF) presently in use by several companies and organizations. It determines how much improvement can be had using PSS powder.

BIF (Burn Improvement Formula)

(Bullet radius/3.14159) x SC (shape constant) x 1% of the propellant weight. Let's plug in some numbers.

SC (Shape Constant)
- a mathematical absolute in combustion chemistry

Spherical - .815
Extruded - .8735
Flake - .7 (varies)

Examples

So let’s take the BIF, SC and a load, put them all together to see what level of improvement PSS can produce.

308 Winchester

You're shooting a 308 Winchester with 42.0 grains of pre-sifted, extruded powder.

Here’s the BIF with SC and known propellant weight.

(.154 (bulrad)/ 3.14159) x .8735 x 0.42 = 0.018 (rounded)

Uniforming bullet powder will produce a 1.8% improvement in your groups.

30-06 Springfield

You're shooting a 30/06, using a 200 grain bullet and 55 grains of pre-sifted, spherical powder.

(.154 (bulrad)/ 3.14159) x .815 x .55 = 0.022 (rounded)

Uniforming bullet powder will produce a 2.2% improvement in your groups.

Conclusion



Propellant sifters are in the hands of testers right now. There has been no official announcement when they will be approved for retail sale.

Improvements to powder uniformity are ongoing. While some naysayers may not be impressed, benchrest competitors will tell you that a 1.8 percent improvement to your groups can put you in the winner's circle.