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RELOADERS CORNER: Picking Propellants
July 11, 2019 glen Zediker 5 Comments
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There are a whopping lot of propellants on the market. How do you choose one? Well, usually it’s more than one… READ WHY

PROPELLANT

Glen Zediker

All we ever really want is a propellant that provides high consistent velocity, small groups at distance, safe pressures over a wide range of temperatures, and burns cleanly, and, of course, it should meter perfectly. Dang. I know, right?

Ultimately, propellant choice often ends up as a compromise and it may well be that the smallest compromises identify the better propellants. Getting the most good from your choice, in other words, with the fewest liabilities.

There are two tiers of basics defining centerfire rifle propellant formulas. The granule form can be either spherical (round granules) or extruded (cylindrical granules). Next, the composition can be either single- or double-base. All propellants have nitrocellulose as the base; double-base stirs in some nitroglycerol to increase energy.

There’s been a good deal of effort expended and applied over the past several years to reduce the temperature sensitivity of propellant. Coatings come first to mind, and I use nothing but these “treated” propellants.

This attribute is very (very) important! It’s more important the more rounds you fire throughout a year. A competitive shooter’s score hinges on consistent ammunition performance. Test in Mississippi and then go to Ohio and expect there to be some change in zero, but a change in accuracy or a sudden excess of pressure and that’s a long trip back home. It’s common enough for temperatures to (relatively speaking) plummet on at least one day at the National Matches, so my 95-degree load has to function when it’s 50.

extruded propellant

Some are decidedly better than others in this. There are several propellants I’ve tried and will not use because I didn’t get reliable results when conditions changed. Some gave outstanding groups on target, on that day, at that hour, but went goofy the next month when it was +20 degrees. Heat and cold can influence pressure in a sensitive propellant.

Single-base extruded (“stick”) propellants are my first choice. A good example of one of those is Hodgdon 4895. These tend to be flexible in maintaining performance over a wider range of velocities, related to a wider range of charge weights. For instance, I’ll vary the charge weight of the same propellant for ammo for different yard lines. I’m reducing recoil or increasing velocity, depending on what matters more. Zero and velocity are different, but accuracy doesn’t change.
H4895
There are a few single-base extruded propellants that show impressive flexibility in load levels as well as in different round structures. This is one of the most flexible I’ve used, and I use a lot of it!

Spherical or “ball” propellants (these are double-base) are a good choice for high-volume production, and also tend to be a great choice for highest velocities at safe pressures. These meter with liquid precision. They, however, tend to be less flexible. That means they tend to work best at a set and fairly finite charge and don’t do as well at much less or more than that, and especially at much less than that. More in a minute.
spherical propellant
Spherical propellants tend to be volume sensitive. My experience has been they’ll perform best when the fill level is a good 90-percent. That means there’s a little smaller gap between one that’s good with, say, 50gr bullets and one that works well with 60s. It’s likely to be two propellant choices, not just one. Generally, spherical propellants do their best when loaded near-to-max.

Double-base extruded propellants (sometimes called “high-energy”) do, yes, produce higher velocities at equal pressures compared to single-base but also tend to be less flexible and exhibit performance changes along with temperature changes. Vihta-Vuori and Alliant are the best known for their formulations in these. Double-base usually burns at a hotter temperature (not faster or slower, just hotter) and can increase throat erosion rate. Some double-base spherical propellants claim to burn cooler. I’m not certain that this is a huge selling point, either way, for a serious shooter, but, there it is.
VV540
Double-base extruded propellants are mighty fuels, but, they tend GENERALLY to be more temperature sensitive and also burn hotter. Now. That’s not always true (I think NONE one of this is always true). With Viht. you can have a choice of double- or single-base in the same essential burning rate; N140 is single-base, N540 is double.

All propellants are ranked by burning rate. That’s easy. That’s just how quickly the powder will consume itself. All reloading data manuals I’ve seen list propellant data in order from faster to slower. For instance, if you’re looking at .223 Remington data and start off with tables for 40-grain bullets, you’ll see faster propellants to start the list than you will moving over to the suggestions for 75-grain bullets.

It’s tough to find a perfect propellant for a wide range of same-caliber bullet weights. Faster-burning propellants tend to do better with lighter bullets and slower-burning tends to get more from heavier bullets. That’s all about pressure and volume compatibility. Again, I have found that a single-base extruded propellant will work overall better over, say, a 20-plus-grain bullet weight range than a single choice in a spherical propellant.
scale pan with powder
Extruded propellants vary greatly in granule size, and, usually, the smaller the better. More precise metering. This is VV540, strong stuff, meters well. There are a few now that are very (very) small-grained (like Hodgdon Benchmark).

The idea, or at least as I’ll present my take on it, is that we want a fairly full case but not completely full. I don’t like running compressed loads (crunching a bullet down cannot be a good thing), and excessive air space is linked to inconsistent combustion. We ran tests upmteen years ago with M1As and found that out. Many details omitted, but here was the end: Settling the propellant back in the case prior to each shot absolutely reduced shot-to-shot velocity differences (the load was with a 4895, necessary for port pressure limits, and didn’t fully fill the case).

Generally, and that’s a word I’ll use a lot in this (and that’s because I know enough exceptions), spherical propellants have always performed best for me and those I share notes with when they’re running close to a max-level charge. More specifically, not much luck with reduced-level charges.

Too little spherical propellant, and I’m talking about a “light” load, can create quirky pressure issues. Workable loads are fenced into in a narrower range. This all has to do with the fill volume of propellant in the capped cartridge case, and, as suggested, that’s usually better more than less. That further means, also as suggested, there is less likely to be one spherical propellant choice that’s going to cover a wide range of bullet weights. That’s also a good reason there are so many available.

With some spherical propellants, going from a good performing load at, say 25 grains, and dropping to 23 can be too much reduction. One sign that the fill volume is insufficient is seeing a “fireball” at the muzzle. Unsettling to say the least.

Spherical propellants also seem to do their best with a “hot” primer. Imagine how many more individual coated pieces of propellant there are in a 25-grain load of spherical compared to a 25-grain charge of extruded, and it makes sense.

However! I sho don’t let that stop me from using them! I load a whopping lot of spherical for our daily range days. We’re not running a light load and we’re not running heavy bullet. We are, for what it’s worth, running H335.

So, still, how do you choose a propellant? Where do you start? I really wish I had a better answer than to only tell you what I use, or what I won’t use. There are a lot of good industry sources and one I’ve had experience with, including a recent phone session helping me sort out Benchmark, is Hodgdon. You can call and talk with someone, not just input data. Recommended.

When it’s time, though, to “get serious” and pack up for a tournament, I’m going to be packing a box full of rounds made with a single-base extruded propellant that meters well. As mentioned before in these pages, I have no choice in that, really. I’ll only run the same bullet jackets and same propellant through the same barrel on the same day. I need a propellant that works for anything between 70- and 90-grain bullets.

With time comes experience, and I know I sure tend to fall back on recollections of good experiences. I admittedly am not an eager tester of new (to me) propellants. I have some I fall back on, and those tend to be the first I try with a new combination. There are always going to be new propellants. That’s not a static industry. I may seem very much stuck in the past, but I no longer try every new propellant out there. I like to have some background with a propellant, meaning I’ve seen its results in different rifles and component combinations. Mostly, I ask one of those folks who tries every new propellant…

There is a lot of information on the internet. You’re on the internet now. However! There’s also not much if anything in the way of warranty. If you see the same propellant mentioned for the same application a lot of times, take that as a sign it might work well for you. Do not, however, short cut the very important step of working up toward a final charge. Take any loads you see and drop them a good half-grain, and make sure the other components you’re using are a close match for those in the published data.

One last: Speaking of temperature sensitivity: Watch out out there folks. It is easily possible for a round to detonate in a rifle chamber if it’s left long enough. Yes, it has to be really hot, but don’t take a risk. A rash of rapid-fire can create enough heat. Make sure you unload your rifle! Here’s an article you might find interesting.