Beware of moisture when reloading

By PIERRE VAN DER WALT – For the competitive shooter or the reloader hell-bent on high precision and consistency, it is undoubtedly worth it to properly control the moisture content of the propellants used. 

 

Smokeless powders are complex chemical formulations typically based on nitrocellulose, sometimes combined with nitroglycerine (double-based powders), and stabilised with additives to prevent degradation. These powders are manufactured to exacting standards but remain chemically active, and physically porous and hygroscopic, meaning they absorb moisture from the environment.

In short, smokeless powder is not hermetically sealed against the environment. It breathes, and what it breathes in is water vapour. Propellants are loaded with moisture levels between 40% and 55%.

Humidity affects smokeless powder in two primary ways: chemical stability and ballistic performance.

Chemical stability

• Long-term exposure accelerates nitrocellulose breakdown.
• Moisture reacts with stabilisers, reducing their effectiveness.
• Acids form, leading to sour odours, clumping or discolouration.

Ballistic performance

Short-term exposure alters burn characteristics. Moisture reduces energy density, lowering velocities. Uneven absorption creates erratic ignition. The result: cartridges that chronograph slower than expected.

This graph shows how much moisture can potentially be absorbed from the atmosphere by propellant.

TAKING PRECAUTIONS

In the flying sector, they refer to pilots who fly by the seat of their pants as “bush pilots”. For the “bush reloader”, the impact of moisture content is not that important, but for the precision and competitive reloader, it is.

Humidity is essentially invisible and does not announce itself until it has already compromised  your propellant. However, any of the following signs can be interpreted as a sign of a potentially compromised propellant:

• clumping
• colour changes
• oily residue
• acrid odour

For reloaders, vigilance against moisture is as important as vigilance against double charges. The expensive solution is to install an air-conditioning system with humidity control capability in the reloading room and run it at a selected atmospheric level every time before reloading. Furthermore, you should only open propellant cannisters at the selected atmospheric conditions, which can be room temperature and a selected humidity level in the region of 40%-50%.

A cheaper system is to use potassium carbonate (K₂CO₃) to stabilise the moisture content of propellants at around 43%.

Create a saturated solution of potassium carbonate and water and place that, together with an open propellant cannister, in an airtight, sealable container like a clear plastic bottle with a wide mouth (for easy access). Seal the container and let it stand for about five days. Then remove the stabilised propellant and seal the cannister well. I recommend painting the screw cap joint with nail polish and then wrapping electric tape around the joint as an extra precaution against moisture intrusion. This eliminates propellant combustion inconsistency.

Propellant must then be stored in an air-still, temperature-consistent environment. For most of us, a cupboard is good enough, but some guys place the cannis￾ters in airtight plastic range or storage crates and place a desiccant inside the crate.

RISK ANALYSIS

Imagine you develop a maximum load with a “wet” propellant and then later use “dry” propellant to load! The load can then, for example, deliver 140 fps higher velocity if nothing else has changed.

It is not that simple, though. Dry propellant is lighter than wet propellant burdened with moisture. To get to the same charge weight, the chances are that you will load more granules of dry propellant to equal the weight of the wet propellant.

The combination of faster combustion and extra propellants can be potentially catastrophic.