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Not sure how useful this is, but it's kinda like a suggestion, you can choose to use it or not based on your particular situation. Nonetheless, it is interesting.

I was loading and comparing new Sig brass ($31/100) against new Lapua brass ($60/100) for 5.56 loads and found that the Lapua brass actually has a greater weight variation than the Sig brass. So I loaded up two 5x5 ladders, one for each brand of cases and took off to the range and chrono'd them. I used Berger 77 gr OTM (#22101) and Reloder 15 powder. Here are the results in table form:



Looks like Christmas decorations doesn't it! Well, before we jump into the data, let's clear up the colors. When I go to the range with reloads, I chrono and record every shot. I even chrono 5 shots of IMI 77gr as a reference point. IMI 77g is hot ammo, so not only does that give me a velocity indicator, it also gives me pressure signs on the case and here's how 6 IMI cases looked that I shot over the past three days. The photo isn't that sharp, but you can clearly see the marks on the IMI cases on the right. IMI has hard primers so primer indications can be misleading. In fact, the primers are so hard, most IMI rounds will NOT ignite in my bolt guns.



If you look at my loads, on the left, you may see primer cratering, but that's because Federal 205M primers are pretty soft. Someone mentioned in a post recently that he doesn't use Federal primers in AR loads because they are soft and could slam fire. That in itself is something to think about!

But, getting back to the colors. I record my velocities using a Surface Go laptop/tablet. I use an Excel spreadsheet application to enter the velocities and as I shoot, I get running calculations of average velocity, ES, SD, and average energy. In addition I use colors to tell me more. I use conditional cell formatting to automatically pick the high and low velocities. Red is the high and green is the low.

I put the yellow in to remind me that something happened on a particular load. In the above example, the yellow identifies all the rounds where the bullets seated more loosely than the rest.

In addition, as if that weren't enough, I get a running chart showing how the average velocity and SD is looking for each group. For example, at the end of the 5x5 I have this - instantly at the range:



You may have noticed that the first velocity of the 5th charge, 24.9 gr, has been commented out. You may also notice that it is far slower than the other four shots. It's not that it isn't real, it is, but i don't feel it accurately represents the norm for this charge. Sometimes something just gets out of line with the other data - ever hear of a flier or outlier? Well, sometimes these are too pertinent to ignore, but in this case I feel it would skew the data.

And over to the right of the table, that's the change in average velocity from one charge to the next.

And, you probably have heard me say a dozen times that velocity variation is essentially a non issue at short ranges. Well, here's what that 5th group produced. The fifth group, slow shot and all is about 1-1/2" above the lower right red dot. Oh, that slow shot is that hit just to the right of the group.



Hmmm, maybe I should get back on topic. :redface: I guess I said all that to say this, notice from the first two tables I posted, the Lapua cases are faster with the same load and same gun and same temperature. You can actually see it better from a chart of the tables:



It is interesting to note that for the first three loads, the two produce essentially equal velocities. But from there, the last two loads start to separate with the Lapua producing significantly faster velocities.

It is important to understand, the increased velocity from the Lapua cases is NOT free. All else being equal, and it essentially is for this case, the only way the velocity can increase is for the pressure behind the bullet to increase. So it's worthwhile knowing that Lapua cases may be faster at higher charges, the pressure also has to be higher.

OK, I'm done, you can stop reading now - don't forget a "like". :biggrin2:
 

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There are so many variables that cause significant differences in velocity that it must be maddening trying to keep track of this, Tangle. I'm not sure how this is all going to play out, but I do appreciate you publishing you data. Better be careful, though, the FBI is going to want to hire you to tell them what to shoot!
 

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View attachment 293366

Meanwhile back at Tangles house..........
That's too near right :redface:

My spreadsheet also automatically gives me plots of the velocities of the individual charges. For example, here's what the 5 velocities look like from the 24.9 gr charge:



It's pretty clear that first velocity was way low compared to the other four.
 

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If you look at my loads, on the left, you may see primer cratering, but that's because Federal 205M primers are pretty soft. Someone mentioned in a post recently that he doesn't use Federal primers in AR loads because they are soft and could slam fire. That in itself is something to think about!






Federal primers in AR loads because they are soft and could slam fire. I have Federal primers in my AR , M1A and 1911 for years. Yes, they are softer then the rest. But I have never seen or heard about a slam-fire because of them, being soft. If so there is some thing else going on.
 

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Data! And you clearly have too much free time :smile:
I'm retired! I now have time to do all those things I never wanted to do in the first place. :tongue:
 
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