Welcome back! We’re onto Part 3 of our Accurate Reloading By Chronograph series of articles here. In part one we discussed briefly the idea behind our reloading method. In part two we took our first trip to the range and reviewed the results. Now, in part three, we’re going to refine those results further! The idea is to really close in on what charge weight gets you the results you want with the bullet you chose. You want to get as close to your velocity goal as possible without running into pressure. In the end, accuracy is more important. If you have to drop a little velocity to avoid pressure or get a tighter result on the chronograph…do it! Now let’s get back into it!
Step Three: On our next trip to the range we loaded five rounds at three different charge weights. Five rounds at the charge weight producing 2996, five rounds 0.1gr lower, and five rounds 0.1gr higher. The idea was to take the results from step two and refine them. The target muzzle velocity was 3000fps so the x8.4gr load was a good place to look. It had an SD of 5fps but only across three rounds. We want to fire slightly longer strings to confirm that result. We also want to check a touch higher and a touch lower to see if the slight change does even better. Remember we’re jumping in .3gr increments here so we haven’t tested x8.3gr or x8.5gr. Those strings were fired through the same rifle using the Magnetospeed V2 chronograph with the following results:
- x8.3gr H4350 – 2988fps SD 11fps
- x8.4gr H4350 – 2995fps SD 3fps ES 9fps
- x8.5gr H4350 – 2994fps SD 4fps
When we analyze the second days data we see a few interesting things. The purpose of the second day or second trip to the range is to refine the data from the first trip. The first thing we were looking for, on the first trip, was velocity and pressure data. Once we had that, it becomes time to look into refining the data into a consistent load. We picked the x8.4gr charge weight because it gave us the highest muzzle velocity, and the most consistent velocity, without signs of pressure. The numbers actually got even better with a longer string. The SD (Standard Deviation – How far off the average speed is each shot likely to be) reported by the Magnetospeed was 3fps and the ES (Extreme Spread – Maximum deviation between fastest and slowest rounds) was only 9fps! Keep in mind that single digit SD is what most guys are gunning for and we didn’t even have an ES jumping into double digits here!
Don’t Go Crazy
We shoot tactical rifle matches, not benchrest, so we tend not to obsess over the difference between 5fps and 3fps for standard deviation. Lower is always better, but if we land on a charge that yields 9fps instead of 5fps SD there won’t be any tears shed over that result. For our accurate reloading method we do load development until we produce a cartridge that gets us a single digit standard deviation and we call it a day. If you wish to further refine things on your own, that is not discouraged and we wish you well. Play with the seating depths and you can probably produce even better results. The DTACs are supposed to be pretty seating depth insensitive so we didn’t bother with a test. The beauty of this method is that it can be scaled. If you have higher accuracy requirements, you can do more testing. If you’re happy with 1/2 MOA and single digit SD…this method will get you there efficiently.
For the sake of this article we called it good when we saw 5fps and that decision was only reinforced when the follow up yielded 3fps. If you’re using VLDs which are known to be fussy about seating depth and jump distance, then further testing is likely a good idea. Keep in mind the age of your barrel. I suggest putting a minimum of 100-150 rounds through a new barrel prior to beginning load development and your accurate reloading process. The reason is because a new barrel, at least in calibers like 6.5 Creedmoor and 6×47 Lapua, will tend to pick up speed as it breaks in. It may pick up as much as 200fps, so it’s worth noting. You don’t want to do all your load development at a round count of 10 rounds only to have to redo it again at 150+ rounds because the projectiles are moving down your bore faster and thus your load is no longer properly tuned to your barrel!
So in summary: load three rounds at a time in 0.3gr increments from WELL below maximum published charge weight up to the max. Pick the fastest rounds, that are showing low standard deviation and extreme spread numbers on the chronograph. If you need to reference powder manufacturers data read our article on that subject here. If you need more information on what standard deviation and other terms mean, we recommend this article. Once you’ve picked a charge weight that gets you the velocity you want, start testing in depth. Load up 5 round strings at the charge weight you picked, as well as 0.1gr and even 0.2gr higher and lower than that charge. It just depends on how quickly the numbers tighten up and run slack again. Run the longer strings over the chronograph and pick the best one! In the next part of this series we’ll talk about how to measure the performance of your new load and see if it’s good to go, or needs further refinement! We’ll be doing a little more group shooting and some distance shooting to check performance! If you have anything to add or a question, please do so below in the comments!