The Evolution of Load Development:
What is your goal? Is your intent to reproduce your favorite factory load for your hunting rifle, or is it to develop a load for a new rifle of the long range persuasion? This represents opposite ends of the spectrum and for sure will dictate how much you do, or don’t do, to achieve your goal. With that in mind, the purpose of this information is to look at generalizations and methods that can lead to the same results.
Focusing on long range capable loading, and not shooting equipment, it should be noted that the quality of components you use will have a direct impact on your finished product. The brass you decide to use will be of utmost importance. Let us assume everyone knows how to uniform their brass, and everyone knows skipping steps will lead to less return on your effort. Fully uniformed brass (fire forming included) will give the best results, period.
Choosing a powder or powders to test comes with lots of options. Reloading manuals can give you a great place to start. Burn rates particular to caliber and bullet weight deserve attention. Burn rates generally have a fast end and a slow end recommendation for each caliber and bullet weight. They all come with a recommended maximum, and some even give a starting load. Let’s assume everyone knows ignition of the powder results in a gas that causes pressure and creates harmonics and results in velocity. Being ever cautious of perceived signs of high pressure, and monitoring resulting velocities will give you data for comparison from powder to powder.
Besides charge weight, other things you control that can influence pressure include (but are not limited to), seating depth and neck tension. The result of seating a bullet against the lands, as well as seating deep into the powder column must be understood. Neck tension can be addressed in a couple of ways, like choosing to turn necks for uniformity, and using a bushing-type die.
The quest for accuracy that must be accompanied by low extreme spreads and standard deviation varies, as we all know, from rifle to rifle for many reasons. As combustion pressure relates to harmonics, harmonics become essential in the accuracy equation as the harmonics are broadcast through the delivery system, the barrel.
I am fairly certain there exists equipment and computer-generated graphs that can map barrel harmonics. As to the affordable availability of using this technology, or being able to have personal tests done by others, I have no clue. I mention this because I quite believe if powder tests could be accompanied by harmonic maps, we would see a whole new level of accuracy to include low es and sd.
Now, finding that best load for your rifle. The purpose of this writing is to address some false generalizations, like it only takes 10 rounds to develop a load. 10 round ladder test and I’m done. This information is best used by those who already have collected obscene amounts of data and can tell you off the top of their heads what powder and how much. A 10 round ladder test and there’s no need to run up your round count on your barrel, and then at a later point mention they don’t even try to develop until after they have a hundred rounds down the bore to fire form the brass. Round count is round count . . .you now have 110 rounds down your tube and still need to do more testing for final load. 10 round ladder gets you very close IF you already know and anticipate results. Then there’s seating depth and es/sd, but you already have a good idea how that’s going to turn out as you have previously tested that and already have that data.
We recently did load development on a new rifle. We started with new brass, pulled a seating depth based on previous experience, and started loading in increments of two tenths. We started with a powder we are confident with.
Once we started shooting, everything was on the Lab Radar. We shot 3 shot groups from start to finish so we would have data to identify flat spots and nodes, the same as you do on a ladder test. We were able to see how the groups correlated to the flat spots to determine nodes. As expected, we had one low and one high node within our range of pressure. So in essence, we combined merely fire forming brass, with graphing nodes and flat spots.
By the time we approached 100 rounds, we hit the “barrel speed up” point which is another reason folks fire form brass (two birds with one stone, fire formed and speed up done). Fire formed brass gives better es/sd than new brass, so rightly so, it’s necessary.
Once we hit the speed up and confirmed it with a couple more groups, we did the math and reduced loads accordingly to bring velocity back down to the node we desired. Then we confirmed our velocity and compared the group to see it was no different than the group of the same velocity at the higher charge weight before barrel speed up.
Once this was complete, we took 3 other powders to the same velocity nodes to compare them to our best groups. Even though I’ve recently read people state they can get any powder to shoot well, so long as it’s at the same velocity node . . . well for us, that is simply not the case. It might get you close, but it’s not exact. That takes me back to harmonics mapping . . . thinking different burn rates even at the same velocity may print different harmonic maps.
We shot a final 5 shot, .35 group single digit es to wrap up this project in 112 rounds and have usable data to support later projects of the same caliber. My thought? If you need to fire form your brass before you start development, why not take the data from that exercise. Unless of course you already have that data, but 100 rounds fire formed and 10 round ladder test vs. our 112 rounds to complete development is in my mind a wash. Obviously there is more than one way to get this done netting the same results.
R. Mckinnon
Recent load development with a Benchmark barrel 7mm Rem Mag with a Berger 175 EL, Reloader powder