What additive in powder makes is less sensitive to temperature change?

[rap36case]

I'm a chemist. I know formulation of products make a big difference in perfomance by optimizing proportions of components. Usually there are only a handfull of components used in any industry. Analytical chemists and formulations chemists work as teams to deformuate competitor products (it's the real world out there).

So, anyone have any ideas as to what makes one powder more temperature sensitive than another?

 

[Laurie]

Mic McPherson (Metallic Cartridge Handloading, Safari Press 2013) puts it down to two factors. First, ADI uses hardly any graphite glazing. He speculates that the manufacturer uses 'an energetic conductive polymer' either in the ingredients mix or as a coating. By promoting faster ignition this may reduce temperature sensitivity. Second, McPherson says that NC powders are 'plastic', ie deformable. Plasticity is a function of temperature and a cold propellant charge deforms less than a hot one as pressure builds in the case after ignition. Powder kernels are covered in microfractures left after the solvents used in the NC propellant manufacturing process are evaporated out. His hypothesis is that when the charge is cold, the kernels are less plastic, deform less under pressure, and the micro-fractures remain open giving a larger overall combustion area. When hot, they are forced closed, reducing the overall burning area.

ADI, says Mr McP,

"............ accomplishes this extremely desirable goal (temperature insensitivity] through precise control of size, number and depth of microfractures ......... "

I'm not sure how good / accurate this explanation is, but it's the only one I've seen to date.

 

[CatShooter]

So, anyone have any ideas as to what makes one powder more temperature sensitive than another?

Nitroglycerin is what makes powders very sensitive to temperature changes - that being eliminated solves 70% of the problems...

But as too what manufacturers do too further stabilize single base (nitrocellulose) is fairly new, and not commonly known. Even in the industry.

Mic McPherson (Metallic Cartridge Handloading, Safari Press 2013) puts it down to two factors. First, ADI uses hardly any graphite glazing. He speculates that the manufacturer uses 'an energetic conductive polymer' either in the ingredients mix or as a coating. By promoting faster ignition this may reduce temperature sensitivity. Second, McPherson says that NC powders are 'plastic', ie deformable. Plasticity is a function of temperature and a cold propellant charge deforms less than a hot one as pressure builds in the case after ignition. Powder kernels are covered in microfractures left after the solvents used in the NC propellant manufacturing process are evaporated out. His hypothesis is that when the charge is cold, the kernels are less plastic, deform less under pressure, and the micro-fractures remain open giving a larger overall combustion area. When hot, they are forced closed, reducing the overall burning area.

ADI, says Mr McP,

"............ accomplishes this extremely desirable goal (temperature insensitivity] through precise control of size, number and depth of microfractures ......... "

I'm not sure how good / accurate this explanation is, but it's the only one I've seen to date.

None of McPherson's explanation fit the know manufacturing of single (or double) base powder burning characteristics of nitrocellulose. It is extruded through a perforated plate like spaghetti, and sliced as it comes out - there are no micro fractures.

Smokeless powder burns (actually it deflagerates) in a two stage process - in the first stage, it breaks down into a group of gases, and those gases deflagerate at a flame front, heating the grain, causing more gas to be given off.... it is the depth of this gaseous layer that is responsible for the progressive nature of smokeless powder, i.e., being able to change it's burning rate while burning. This is all know in the propellant industry - no secrets here.

 

[LHSmith]

I've read many of Mic McPherson's articles in Precision Shooting through the years, and was impressed with his knowledge. Don't recall a single article penned by a catshooter......ever. A proprietary coating would be my best guess also.

 

[CatShooter]

I've read many of Mic McPherson's articles in Precision Shooting through the years, and was impressed with his knowledge. Don't recall a single article penned by a catshooter......ever. A proprietary coating would be my best guess also.

When Precision Shooting published an article that stated that bullets slow down until the speed of sound, and then turn down at a 45 degree angle and go straight to the ground, I let my subscription drop.

I knew David Brennan (we live close and his office was about 8 miles from me).... David was a very lost and sad man, and though he liked guns, he knew little about precision shooting, which was the reason his magazine failed.

He also paid next to nothing for articles, and they would sit in a file for years until he needed to fill a space... based not on the article, but how many column inches he had to fill for the month.

 

[LHSmith]

Not sure how your taking the opportunity to discredit Brennan as an editor has any reflection on McPherson's expertise? You know Mic also?
By the bye, Brennan did accumulate shooter points in the early years of Benchrest, so he must have had some clue about precision shooting. I believe he also authored an article or 2 in the book The Benchrest Primer.

 

[Laurie]

Nevertheless, it remains the only printed explanation I've seen as to why Hodgdon single-base 'Extreme' powders (none of which have nitrolgycerine added, so we can discount any effect there). So, I await with some interest any informed comments from those who know just what ADI has done to achieve the effect.

So, smokeless powders deflagrate in a two stage process. And ..... ? This applies to every single-base extruded tubular propellant, but obviously not identically. Stating this doesn't add anything to the OP's question as to what ADI adds, removes, or does differently in creating this characteristic.

FWIW, some ball powders which DO contain nitroglycerine of course are acquiring a sound reputation for consistency and much reduced temperature sensitivity, in particular those manufactured by PB Clermont in Belgium which are sold as canister propellants under the Ramshot name, and in the US, as Accurate brand spherical grades.