Reloading - Different powder types
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- Last updated: 14/02/2022
All aspects of reloading are not a singular consideration. In fact, the whole picture has to be assessed, as lots of little procedures lead to the ultimate reload, leave one out and the whole shebang will collapse.
Probably one of the major components, after the case and bullet, is the powder type, weight and loading. Get this wrong and you will not only get poor reloads but also may suffer some dire overpressure consequences.
Barrels have a resonance to them when fired, so changing the powder weight by ½ grain and sometimes ¼ grain increments, will have a marked effect on performance. What you will notice from the group sizes is not only a change in overall size, but also the orientation of the group, either vertical or horizontal. This is because every load puts different vibrations through the barrel and so the harmonics, as the bullet travels down the barrel, will alter with movement at the muzzle end, influencing accuracy. With a correct powder, you are trying to achieve a load where the bullet exits the barrel when it is in exactly the same orientation, shot for shot. This means that the correct barrel timing, powder, primer and bullet (type and seating) all play their part. There will be a sweet spot of harmonisation with a particular load of powder and whilst experimenting, that will drastically affect the group size and muzzle velocity of a reload.
A significant part of reloading is getting close to that goal of one-hole groups while achieving low SD values. However, if you are using the wrong powder type, it just isn’t going to work and many hours can be wasted.
Powders burn at differing temperatures and for different durations of time (burn rate). So, this turbulence of the powder combustion in the case needs to be consistent to provide 100% efficiency each time. Using the wrong type or burn rate can cause incomplete burn and over or under pressure, which is easily seen as it changes velocity and horizontal spread to groups, due to changes in barrel timings.
Most modern-day powders are single or double based propellants, meaning that Nitrocellulose (NC) single based can be combined with Nitro-glycerine (NG) to form a double base/high energy powder. The trouble is that powders can be all manner of sizes and shapes, with mixtures of deterrents/retardation coatings, fouling suppressors and flash eliminators, so where to start?
The powder burns in an oxygen-free environment of the barrel due to hydroxyl groups of cellulose being substituted for Nitro ones. Stabilizers are used to prolong storage life, as Nitrocellulose deteriorates quite quickly, and graphite is often added to the surface to stop static electricity build-up. All are important, but the most significant to us reloaders is the use of surface treatments that control the burn characteristics of the powder. They slow the initial ignition down to provide a progressive burn and thus the highest velocities, while maintaining safe pressures for longer. Basically, it does not all go off at once!
You are wanting the chemically stored energy of the powder to be converted to kinetic energy, with safe pressures and maximum efficiency. However, this is not always 100% due to thermal/heat conversion. That’s why your barrel gets hot.
Now you can see why choosing a powder that is right for your load is very important. There is a lot going on unseen inside the chamber and barrel of your rifle.
The energy that you need to propel a bullet all comes from the stored energy in the powder itself, so the cartridge/ reload performance is significantly altered by changing the powder type. It’s a balancing act, as often compromises have to be made between best accuracy and best velocity. Seldom do the two live well together and often the best load is not at maximum pressure.
You are after a powder that produces uniform pressures and muzzle velocities that optimize for the case size, plus an efficient burn rate and charge to volume ratio (how full the case is). Add to this temperature changes, moisture content, differing lot numbers of production and it can be a chore achieving the best load.
The chain reaction of powder ignition after the primer is ignited is largely influenced by the differing types of powder used. As peak pressure is reached, very soon after the bullet starts to travel up the bore, pressure soon drops off as the increased volume caused by the moving bullet negates it. This is why the right burn rate is critical for best results.
If you change the shape of the powder you use, it can greatly affect the performance with regard to velocity and pressure. Flake, ball, tubular/extruded and single or multi-perforated grained powder, all have their characteristic performance values. In short, the size and relative thickness of the powder affects its burn rate too, determined by the so-called web thickness, i.e. surface to core thickness.
The change of the surface area of each powder type causes a change of ‘form function’ or combustion.
An increase in form function is described as progressive (Tubular powder) and a decrease is degressive (flake and ball powder). Long tubular grains are usually quite neutral. The shape can have a marked performance on ballistics as progressive powders achieve good velocities at lower maximum pressures and vice versa for degressive powders.
Flake-type powders are very common as they are easy to manufacture, with no special technique. They are good for a wide range of applications from pistols to rifles and allow a reload to fill a case very well, due to their good packing density and compressibility. However, it must be stressed that a good packing density is after it has settled in the case. Some flake powders, after metering into the case, can settle by up to 25%, some even 35%! That’s why with flake powder it is essential to use a consistent loading technique to maintain a consistent mass. That’s why tapping a case after powder dispensing will settle or drop the powder level. Short, stubby tubular powder and flattened ball-type powders suffer from the same issues.
Tubular or extruded powder is probably the most common type of rifle powder and is available in a variety of diameters and lengths, with a porous or solid construction, dependent on how the burn rate is deduced. Due to the shape of these types of powders, fewer additives are used and thus size is not necessarily indicative of burn rate. In fact, short cut tube powder is popular due to it metering well through a powder dispenser, as it stops the crunching between measuring bowl and frame. That is why I switched from my culver powder measure to weighing individual weights of powder on a beam scale, so I could achieve an absolute precise load.
The tubular or extruded powders also have less deterrent in them, which make them relatively clean-burning, allowing more time between cleaning the barrel. Unlike ball powders, extruded powder is less temperature sensitive, and so can often be far more reliable in a wider range of environments.
Onto ball powder, which is a double based propellant that was invented by the Olin ammunition company back in the 1940s. It was devised to be stable in a spherical form with the addition of NG to the mix. Also, by consequence, it meters, packs and burns consistently. The burn rate is uniform and often the sphere-like powder can be flattened or squashed to increase surface area and thus influence the burn rate accordingly. Ball powders also have quite a few deterrents within their mix to regulate burn rate and so this ultimately reduces the flame temperature and can prolong barrel life.
Their main attribute is their case packing ability. By being spheroid, you can use a heavier charge of a slower burning ball propellant, compared to a tubular/ extruded powder. Hence, some higher velocities with ball powders can be achieved, but care must be taken not to exceed max pressure, considering their susceptibility to temperature change. Also, as said before, the higher deterrents used in manufacture can cause a far dirtier barrel, which is evident when looking down the bore.
Regardless of what powder type you settle on, Lot numbers are also really key, just like a good batch of factory ammo. When you finalise a good reload, try and buy as much of that powder Lot as possible.
This is just an overview really, as there are so many variances to powder choice and burn rate. I do use the Quickload Ballistic program to help with the initial load set up, as it can warn against pressure and importantly load density, plus burn efficiency too. At the end of the day, you need to try each load out for real in your rifle as every barrel is different and finding that magic load is still partly patience and luck!
Henry kranks - Ramshot Powder - www.henrykrank.com
Norman clark gunsmiths - Reload Supplies - www.normanclarkgunsmith.com
Edgar brothers - Alliant Powders - www.edgarbrothers.com/shooting-sports
JMS sporting - Quickload Ballistic Program – www.quickload.co.uk
Hannam’s - Reload supplies - www.hannamsreloading.com