How do you find the optimal rifle powder and load? Rifle load development can often be a trial-and-error effort where you have to put a lot of rounds through your barrel to learn what it likes best. The problem is that we’re trying to detect relatively minor performance differences between loads (e.g., one load has a 0.35 MOA group, and another might be 0.45 MOA). When you’re trying to differentiate between those minor differences, you need a large sample size to know with any confidence that what you’re seeing isn’t simply random noise in the data. (Read my Statistics for Shooters Who Aren’t Math Nerds articles for more details.)
That means if we are going to try a couple of different types of reloading powders and charge weights, then we’ll quickly end up putting hundreds of rounds on our barrel before we find the optimal load. For a barrel like the 6mm Creedmoor that may only have 900-1200 rounds of accurate barrel life, using up a significant portion of that to find a load is sure hard on your wallet! 😉
This guide will show you how to streamline your reloading process and pick the best rifle powder for your cartridge.
The only shortcut I knew of was to try what the top-ranked precision rifle shooters were using, and maybe that would get me on a very accurate load quickly. I published very detailed load data from top 200 shooters in the PRS, and it’s often where I personally go to get an idea of what loads to try:
If you’re looking for another cartridge, you can also browse my personal load data. That’s the page where I save all my load data and reference back to it when I’m reloading.
I will warn anyone thinking about copying someone else’s load data to start with the minimum safe loads from a reloading manual and slowly work your way up to the load. Never assume a load that was safe in someone else’s rifle will also be safe in your rifle too.
Then, a few weeks ago, I came across the book Ammunition, Demystified by Jeff Siewert (view book on Amazon | read my review of the book) – and I’ve learned a ton about ammo! It’s literally one of the best books I’ve ever come across related to precision rifles and long-range shooting. It is written by a ballistic engineer who recently retired after a 40-year career of research and development relating to ammo and firearms, and the book is his way of pulling back the curtain on the “black magic” of ammunition and sharing the facts and insights he learned through decades of research and being an industry insider.
Jayden Quinlan, senior ballistician at Hornady, says that he finds himself pulling this book off his shelf weekly to reference something. It is fascinating, and I don’t think anything like it has ever been published.
Here is the intro to one of the sections in the book:
“I’ve read lots of articles in various publications about the effect propellant has on the dispersion of a given load, most of it well-intentioned, but nearly all is sorely lacking in explanation as to the particular parameters leading to a particular propellant being responsible for shooting a small group size.” – Jeff Siewart in Ammunition, Demystified
Jeff systematically outlines all of the specific factors that cause powders to fire small groups or not. Jeff not only agrees that the powder you use can impact your dispersion but explains all of the intricacies of how powder can change a bullet’s flight.
I won’t spoil it all, but I did want to share a few practical tips that Jeff covers in his book.
There are three primary ways changes in propellant can adversely affect dispersion, even if you put precisely the same weight of propellant in the same case.
- If the propellant is too slow for the application at hand, the case may be filed with powder, but the propellant likely won’t completely burn out prior to the projectile exiting the barrel. The unburned propellant grains subject the base of the projectile to a hail of small, externally applied loads, oriented randomly (around the circumference of the projectile as viewed from the base), that can push the projectile around. While the loads imparted by the unburned propellant grains impacting the projectile may be small, spin-stabilized projectiles are especially sensitive to externally applied loads at their aft end. Another possibility with a propellant that is too slow for the intended application is that it usually results in higher than desired pressure on the projectile base at the muzzle exit. High but variable base pressure at muzzle exit, combined with a mechanical asymmetry at the muzzle (imperfect muzzle crown), can impart variable unbalanced loads to the projectile base, disturbing the projectile flight. …
- If the propellant is too fast for the application at hand, the case will not be completely filled with propellant (if we’re paying attention to pressure limits). With the case less than 100% full, there will frequently be a shot-to-shot variation in the distribution of the propellant in the case as the primer is initiated. Variation in propellant distribution at ignition leads to variations in flame spread through the propellant bed, leading to larger than desired variations of peak pressure, time to peak pressure, muzzle velocity, and in-bore travel time shot-to-shot. … Since there are no straight barrels, variations in peak pressure, muzzle velocity, and action time lead to changes in barrel pointing vector as the bullet exits the barrel, increasing dispersion. In this particular instance, an inert filling, such as powdered baby cereal, over the propellant bed aft of the projectile can prevent propellant from wandering around in the case during handling and chambering and potentially reduce shot-to-shot variations harmful to good dispersion.”
- … and you’ll have to read the book to see the 3rd factor. It’s on page 132.
In the book, Jeff points out several nuanced tradeoffs between different powder characteristics. By understanding the science and physics of what is actually happening, we can make better decisions in terms of what “striking the right balance” might look like for our rifle and application.
Every cartridge has a variety of appropriate powders from which we can choose, which are listed as options in reloading manuals. Which powder should we try first? A professional ballistician often has a sense as to which powders are most likely to produce the smallest groups.
Because Jeff was an industry insider for 40 years, he shares valuable insight in terms of observations that several small-caliber ammunition manufacturers have made in terms of what types of powders seem to be associated with smaller groups. It’s always interesting when you see multiple independent teams come to similar conclusions.
“One interesting observation that has been made by several small caliber ammunition suppliers is that, all else being equal (e.g., for given case/bullet combination and given muzzle velocity), smaller groups are associated with propellants having higher relative quickness. This means that the bullet attains a given peak pressure earlier in its in-bore travel and significantly has reduced base pressure as the bullet exits the barrel. Any tilt of the bullet in-bore with respect to the bore centerline will generate a flow asymmetry at muzzle exit, inducing an angular rate on the projectile. Use of powder with increased relative quickness would be expected to see a reduction in both base pressure at muzzle exit and the frequency of unburned propellant grains exiting the barrel. Both these should help reduce group size.”
When we’re doing rifle load development in search of the smallest groups and best precision, Jeff says what we’re really doing is looking for a powder that burns out completely while filling the case as close to 100% loading density as possible without exceeding the allowable pressure.
Here is how he summarizes a professional ballistician’s approach to load development in terms of what attributes they’re going to look for in a reloading powder:
As partially stated above, the ideal propellant for a particular application possesses these attributes:
- The case is filled to greater than 95%-97% of the maximum bulk loaded density to maximize muzzle velocity.
- Peak maximum operating pressure of the weapon is not exceeded on a frequent basis.
- The propellant grains are completely consumed prior to the projectile exit from the muzzle.
- The propellant is easy to ignite when conditioned at cold temperatures without becoming brittle. Propellants containing nitroglycerine (e.g., double-base or triple-base chemistries) have a reputation for sensitivity to cold-temperature conditions due to the crystalline transition temperature of nitroglycerine being just 15-20° C above the typical -40° C typically specified for operation of military propellants. Below this temperature, the grain can fracture in uncontrolled ways, causing a rapid increase in the burning area of the propellant and a resulting spike in peak pressure.
- The propellant has a low temperature coefficient; its performance is not overly sensitive to increases or decreases in ambient temperature.”
If you’re still reading this article, then I guarantee you’ll love Jeff’s book. There are a ton more nuggets of wisdom in there that I’d love to share, but you should just go buy it!
My next article will dive deeper into Jeff’s last bullet point above, which is rifle powder temperature sensitivity. I’ll share insight from another group of professional ballisticians who literally produce over 100 million rounds of ammo every year. I’ll also quantify what that means to the long-range shooter in practical terms. Stay tuned!
This article is part of a series on rifle reloading data, load development, and reloading components. Here are other related articles that I’ve recently published or plan to publish in the near future:
If you buy stuff off Amazon, use the link below and I get credit regardless of what you get or from what country you order … and you pay not a penny more! Amazon has an affiliate program that pays a small commission when readers use links from my website to buy stuff. You still get your stuff at Amazon’s great prices, and you can help support PRB at the same time.
© Copyright 2025 PrecisionRifleBlog.com, All Rights Reserved.
