Load Development (Part 5)

Thanks for sticking with me, this is going to be a monster post, not so much in it's length but in the amount of detail I'm about to get into.

Data Analysis - Making sense of it all

Up to now all of these steps have been like making a pie, all of the ingredients have gone into the bowl, been mixed, rolled, and stuffed with fruit, if the last installment was like tasting the pie, this section is going to be about how we can make that pie better.

So by now you probably have a bunch of shell casings that are all dirty and waiting for their next reload, maybe you have a chronograph with dead batteries, a sunburn and are in dire need of a shower. However, you also have a very valuable piece of paper that contains all of the data you took from the last trip to the range.

Rather than exhaustively going through every single load, lets make a spreadsheet we can put our data into. Personally, I tend to use Microsoft Excel, because that's what's on my computer, and that's what I've been using for years. Not to create a debate about which spreadsheet is best, any of them will work provided it has functions that SUM, AVG, and Standard Deviation.

Unfortunately, I couldn't find my old test data from when I developed my .223 69gr load, and a number of the other development projects I've done were done with bulk powders, and are proprietary to some of my former employers. But here is some test data from some .308 Loadings I did some time ago, you're welcome to use these loads, however I assume no liability, or make any assumptions about their usefulness for anything. That said:

Barnes 30842 FC IMR3031 41.5 WLR 2.795
2803 2772 2787 2774 2787

Barnes 30842 FC IMR3031 41.5 Fed215 2.795
2771 2773 2796 2763 2731

Sierra 2200 FC Varget 42.0 WLR 2.750
2481 2515 2469 2491 2501 2500 2484 2490 2491 2503

Hornady 190gr HPBT FC IMR3031 38.5 WLR 2.795
2420 2428 2463 2429 2416 2441 2428 2439 2445 2440

As you can see, each of these loads varied, and I kept track of all the components used, the case, powder, bullet type (by manufacturer number), primer, and the OAL.
That said, lets crunch some numbers:

Avg Velocity Standard Deviation
Load 1 2784.6 12.46
Load 2 2766.8 23.48
Load 3 2491.4 12.96
Load 4 2431.2 13.67

Now for those of you who are not too familiar with statistics, and either didn't read, or didn't care to understand exactly what Standard Deviation is, this means that there is a statistical probability that about 75% of the rounds fired will be within 1 standard deviation of the average velocity in column 2.

Generally, the accuracy of ammunition is not an important factor, this is why firearms have adjustable sights, what is important is consistency, so the more identical one round of ammunition is to the next, the higher the probability of you putting bullet after bullet into the bullseye.

In general again, I am willing to tolerate a maximum SD of 20FPS in any rifle ammunition I am producing either for my handloads, or that I will be producing as a factory loading. Ideally, I like all SDs to be under 10FPS, but this is a very difficult goal with rifle ammunition. The reason it is so difficult is the extreme conditions rifle ammunition operates under, every little change will be magnified exponentially. Also, every round doesn't have to be perfect, it just has to be close enough to the last round that no one notices.

So of the loads tested, and the data presented, which loads do you think I decided to keep, and which did I decide to discard?

If you notice, the first two loads are the same charge of powder, same bullet, same case, same everything, just different primer. Interestingly, the winchester primer was both more consistent, and attained a higher muzzle velocity than the federal 215 (large rifle mag) primers.

With this in mind, if you said drop Load 2, you're right! For a number of reasons I don't like Federal primers, usually because they are excessively soft, and thus tend to have problems with consistent seating depth. It seems now there's just another reason I don't have to bother keeping them in stock.

Since I have not really touched on it yet, group size is another one of those important things you need to keep in mind. Unfortunately, I couldn't find any of my old targets from this day of testing, seeing as how it was several years ago, this is not surprising.

So with that in mind, lets talk about what is considered "good" in terms of group size.

Military Standards for small arms ammunition usually specifies a maximum group size with a radius of 2 minutes of angle, (2MOA) which is about a 4" circle at 100 yards, it's worth noting, that in the civilian world, the MOA measurement of a group is a diameter, not a radius. Therefore, a 2MOA radius group is actually a 4MOA group in the civilian world.

For any ammo I consider this an absolute bare minimum accuracy standard, and would consider any experiment that produced results that only met this standard to be a dismal failure. For regular FMJ-BT "blasting" ammo that I use for regular every day shooting, I consider a 2MOA radius to be good enough for production ammunition, 1.5MOA ammo to be good enough to be considered match ammunition, and any ammo that shoots better than this an unbridled success. In general, 1MOA is a tough goal to get to with production ammunition, but it is attainable with handloads. Additionally, a 1MOA envelope the capabilities of the gun start to matter just as much as the ammunition.

Creating consistent ammunition can be quite a chore given all of the choices out there for bullet, powder, primer and case, the magic to getting those numbers where you want them can be quite difficult, but experience in selecting components can help quite a bit.