reloading by chronograph pt2 featured

Accurate Reloading by Chronograph Pt. 2

In Blog by Rich1 Comment

When discussing the AccuracyTech method for accurate reloading, it helps to have a clearly defined objective. This is the process we’ve developed and have used, with success, to develop 1/2 MOA or better loads across a variety of calibers and catridges.¬†This load development project was done over the span of a few days with the end desired objective being: a cartridge and powder charge for a specific projectile, fired from a specific gun, that would yield a Standard Deviation (Or SD) in the single digits and produce group sizes of 1/2″ or less at 100 yards distance with sub Minute of Angle (or MOA) performance out to 800 yards or farther.¬†Now that we’ve defined the objective, let’s discuss the hardware and the method! If you missed the first part of this series, you can read it here!

Accurate Reloading Hardware

What rifle did we use for this? Frankly, this article has been in the works for a while. I wanted to wait till I did another round of load development so I had fresh data. I also don’t typically hold onto erroneous chronograph data after it’s served it’s purpose. Fortunately, while on vacation I did a round of load development on my 6×47 Lapua match gun. To this point I’ve been using Berger 105gr Hybrids at around 3120fps out of the 6x47L at matches. David Tubb of Superior Shooting Systems recently released a modified version of his popular 115gr DTAC bullet. The new bullet has a rebated boat tail and a 1000yd G1 ballistic coefficient of 0.620. That’s pretty remarkable. It put’s a 6mm rifle on par with a 6.5mm rifle firing 140gr Berger Hybrids for wind drift. Being a 6mm, it’s almost certainly shooting flatter. 2850fps with a 140gr bullet is getting up there with pressure and velocity.

So it’s time to do a round of load development with the 115gr DTAC. All the initial load development was done with a Magnetospeed V2 Chronograph for a few reasons. Magnetospeed V2 is much easier to set up than a traditional chronograph. It also doesn’t require a cold range and can be utilized at public ranges with greater ease. While there is a V3 available now, I haven’t had any issues with my V2 so I’ll likely upgrade the components over time.

Accurate Reloading Process

I actually did all this load development in a single afternoon. Two trips to the local range at Cherry Creek State Park. I started by loading incremental powder charges up to maximum charge weight as published by Hodgdon. The powder being used was H4350 but we will not be discussing the charge weights for liability purposes. In the same vein, this is a good time to mention that this reloading technique is meant for an experienced reloader, not a novice or beginner. We accept no responsibility for your actions or their results. If you do something silly and blow your face off, that isn’t something we want coming back on us, and it is why we won’t discuss powder charges, only the technique.

You need to do you own research and reading, and you need to start well below the maximum powder charges published by the powder manufacturers and bullet companies. If you don’t, you run an excellent risk of damaging your gun and potentially injuring yourself or worse. So don’t be that guy, be safe, start low and work your way up checking for pressure signs at each powder charge weight.

Step One: We loaded three rounds at each charge weight from our starting point to maximum. Each charge was loaded in .3gr increments. We have used .3gr increments in the past with good results. The reason being if there’s signs of an accuracy node developing, you can accurately predict the addition or subtraction of .1gr of powder. You can look at the results of one charge, and a tenth on either side of it can be fairly predictable.

For example xx.3gr of H4350 shows an SD of 14, xx.6gr shows an SD of 10, xx.9gr shows an SD of 12. So logically, it’s worth checking the SD of xx.4gr and xx.5gr to see if the SD dips lower before climbing again. If we were making bigger jumps in powder charge, you would have larger gaps between data points and more testing to do to narrow down the optimal charge!

We loaded three rounds to make sure that if there was a pressure sign it was not a fluke or an error in the accurate reloading process. Why only three rounds? The only thing we were looking for on range trip one was data on the muzzle velocities each charge weight produced. Also, whether or not the same charge weight produced any signs of being over pressure in the rifle.

As an added bonus, the Magnetospeed V2 chronograph we used for the test actually produced average velocities and standard deviations for each string of three rounds. Some chronographs won’t calculate SD until you have more rounds in a single string of fire. I’m going to point out here that the purpose of the first set of strings was velocity and pressure data, and not the consistency of the charge, but I won’t lie and say we didn’t look at that also. The goal was to get a 115gr DTAC up to 3000fps+ out of the 26 inch long Criterion Barrel. The Chronograph results of the loads were as follows:

Chronograph Data – H4350

  • x7.2gr = 2906fps SD 19
  • x7.5gr = 2942fps SD 5
  • x7.8gr = 2957fps SD 9
  • x8.1gr = 2984fps SD 2
  • x8.4gr = 2996fps SD 5
  • x8.7gr = 3009fps SD Not available, user error
  • x9.0gr = 3035fps SD 14
  • x9.3gr = 3054fps SD 3
reloading by chronograph pt2 rifle

Rifle with a 26″ barrel, a 10″ suppressor, and a Magnetospeed makes quite the lengthy setup

Step Two: Taking that information we settled on the charge that produced 2996fps as our point to refine. We did this for a number of reasons as well. For starters it was below the maximum published charge weight. When attempting an accurate reloading process we try to leave some overhead in the case, especially when doing the load development in Colorado. For those new to reloading, pressure tends to be lower in colder weather, as the air is more dense and compact. In higher temperatures, where the air thins out and expands, pressure in the case can rise. Thus a load that you develop at 40F in the winter, if loaded close to or above maximum, can have little or no pressure issues at 40F. When the summer rolls around, and you try to shoot the same load at 105F, the same load in the cartridge can be heavily over pressure and dangerous. Additionally the standard deviation for the three rounds at that velocity was quite low, so it seemed like a charge worthy of refinement.

If you look at the Chronograph data you can see how a ladder test works. By incrementally upping the charge weights and measuring the results you can see how the SD (Standard Deviation) numbers tend to tighten up (lower numbers, ideally below 10fps) and then it will start to loosen up again. So if one charge gives you close to what you want and the next charge is going back in the wrong direction you know to check the middle in more detail.

Wrapping Up

In part three of this series we’ll be doing exactly that. We’ll show you how we refined the load development further after reviewing the data from the first range trip. This article is getting long so it’s been split into multiple posts. Don’t let that fool you. This round of load development was done in a single afternoon with around 40 rounds fired and three hours of time. That includes driving back to the house to load the next series, loading them, and driving back to the range for the second trip. This doesn’t have to be a painstaking process that drives the shooter crazy. This is for producing consistent half MOA or better ammunition for tactical rifle shooting. Other shooting disciplines may have more work to do but for what this site is about, this works really really well!

If you have questions or comments, fire away! We like to hear from the readers!

Owner and Proprietor of AccuracyTech, LLC. Rich is a Firearms Enthusiast, Precision Rifle Competitor, and Writer. He is committed to bringing readers quality reviews and articles related to the Precision Shooting Sports. If you have any questions for him, please use the contact form on the site.

Comments

  1. Hi Rich
    I took your suggestion to heart – that is to take the shooter sort of out of the equation in load development. In this case it was taking me out of the equation in determining optimal seating depth.

    I had a good load and wanted to refine it by exploring the impact of different seating depth on precision. I’d tried shooting groups based on different seating bullets different distances from the lands but didn’t find that test conclusive / that’s when your article came in and it made sense to me to try again – this time testing for optimal seating depth using data from my magnetospeed sporter.

    The short story is that I ran the test this morning and ended up with group size clearly favoring 0.015″ from the lands but the chrono data clearly steered me to a 0.010″ ideal seating depth.

    The longer story could involve me posting the chrono data spreadsheet and target images and having a discussion about this method and how you’d resolve a conflict between pure ‘data’ and ‘ down- range’ results on the target. After all, the idea behind the method is to take the shooter out and let the data guide our path so, do I ignore the compelling shot groups altogether?

    Anyway, this is an interesting discussion to have and, if there’s a way to post data and images, this could enhance the discussion and follow through on your article and might even put a happy end to my seating depth quest.

    In any case, thanks so much for all your efforts to promote new thinking and encourage dialog on issues of long range reloading and shooting.

    Cheers!
    Gary

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