.223 es/sd expectations

[eric n]

What es/sd do the f/tr guys expect for a mid range (600) .223 load?
I know that results on paper are the only thing that matter, but.... I was curious as to what people are running with.
My best loads are pretty poor in the extreme spread dept, mid 20's at best. I haven't spent much time tweeking neck tension or changing primers because i've been focused on reading wind better. However, I have a little free time so its time to start fiddling around with the load again.
Thanks,
Eric

 

[Mozella]

I'm relatively new to hand loading and just getting started in F/TR, so don't count me as an expert. However, I am a VERY careful record keeper. I was doing some testing specifically related to muzzle velocity SD since I have been disappointed and mystified with my results so far. Here are the SD values for 15 five shot groups. These are my first rounds neck sized with a bushing die. Previously I've been using a collet die.

The brass was prepared as carefully as possible; i.e. sized, trimmed, flash hole deburred, primer pocket normalized, necks turned, etc.. The rounds are all loaded with IMR 8208 XBR with 69gr, 70gr, and 75gr bullets, so it's not pure apples-to-apples; but perhaps it will give you a data point or two.

I'm not thrilled with the average SD for the day, but I'm happy that it seems to be an improvement over my previous tests, some of which produced really bad SDs.

I've made several very careful studies of SD vs MOA, SD vs Mean Radius, SD vs Vertical, etc. I've scored and logged over 2000 rounds in the past few months.

I have found a VERY slight correlation between low SD and good performance, but just barely and you have to look hard to find it. I scan all my targets and measure them with a computer program, so I think I can speak with some confidence, at least as far as my last 2000 rounds are concerned.

Here are yesterday's SDs, all five shot groups. The 20.95 is the only factory ammo in the bunch (Black Hills).

8.17
9.58
9.91
10.22
11.41
13.29
14.36
14.59
15.63
16.12
18.29
20.95
22.42
30.45
31.02

 

[eric n]

Thank you for your replies.
I agree with what you say gstaylog, and have read Mr. Salazar's article about it as well.
I am admittedly a bit lazy with the chrony but decided to work up some new loads and test what I am running now.
My accuracy load is 24.8g varget, 80 vld, cci 450 primer. es is 44,( I was writing them down and hadn't bothered scrolling to the sd but it wasn't much of a bell curve.) and it holds great vert.
I had retested some of the loads in my notes that had low es/sd at 300 today and the results were disappointing. 1 1/2 to 2 '' of vertical... es of 44 puts up a waterline. Is that normal?

Thanks for responding Mozella. The new loads I was working up were with 8208 xbr. How far above book max did you get?
I stopped testing before I saw pressure because I was so far over book max and the speeds looked like they had a ways to go.

 

[raptor1ronin]

Thank you for your replies.
I agree with what you say gstaylog, and have read Mr. Salazar's article about it as well.
I am admittedly a bit lazy with the chrony but decided to work up some new loads and test what I am running now.
My accuracy load is 24.8g varget, 80 vld, cci 450 primer. es is 44,( I was writing them down and hadn't bothered scrolling to the sd but it wasn't much of a bell curve.) and it holds great vert.
I had retested some of the loads in my notes that had low es/sd at 300 today and the results were disappointing. 1 1/2 to 2 '' of vertical... es of 44 puts up a waterline. Is that normal?

Thanks for responding Mozella. The new loads I was working up were with 8208 xbr. How far above book max did you get?
I stopped testing before I saw pressure because I was so far over book max and the speeds looked like they had a ways to go.

I run 8208xbr with a 28" barrel. I use 24.3 and get 2960fps and the accuracy is awesome. I'm .20 off the lands using a 80VLD

 

[eric n]

Thank you raptor1.
I chickened out a grain and 180 fps short. I had no pressure signs but the highest charge loaded was 23.4, I will have to push on a bit more as it seems everyone who uses this powder likes it.

Btw Mozella.... That is very good sd , thanks for taking the time to post it.
How are you measuring your charge load?

 

[raptor1ronin]

Thank you raptor1.
I chickened out a grain and 180 fps short. I had no pressure signs but the highest charge loaded was 23.4, I will have to push on a bit more as it seems everyone who uses this powder likes it.

Btw Mozella.... That is very good sd , thanks for taking the time to post it.
How are you measuring your charge load?

I also use 23.5 for my 80grn SMK .20 off lands loves that node too vol is 2850fps. I found that the next node was a little better with no pressure signs. Brass life has been good 5 reloads so far with good primer pockets. I anneal after every 3 reloads.

 

[Mozella]

Here is a chart showing Muzzle Velocity SD vs MOA (red plus signs) and Group Height (blue minus signs) for 713 five shot groups which I recorded this Spring and Summer. That's 3565 rounds.

SD vs Performance

Realize that many of these 5 shot groups were associated with load development; therefore, they don't reflect the best possible performance because so much of the tested loads are less than optimum. Nevertheless, the data shows that there is nearly no correlation between SD and performance. The MOA data trend line shows a very slight improvement in group size with smaller SD. But the Group Height trend line is nearly flat.

Can it be that SD has nothing to do with vertical group measurement? I find that hard (nearly impossible) to believe, yet these 3565 rounds show exactly that. You can't see it on this small chart, but one 5 shot group with an SD in excess of 120 had a height of only .085". Go figure.

If I take a look at a better data set comprised of decent shots less than .7MOA and decent SD numbers less than about 40 associated with my ever improving load development, the MOA and Group Height trend lines show that low SDs gives slightly improved performance, but just barely. The trend line isn't quite flat, but darn near. The slope is .003 for those who study such things. That's pretty flat.

I suspect not many people study their SD data this way and just assume low SD's go with good groups. One would certainly think so, but my data doesn't prove it. It just barely even hints at it.

I'd love to see someone else graph a few thousand rounds to see how their MOA vs SD looks.

To answer earlier questions about how far over max recommended charge weight I load, the answer is I don't. In fact my best load for Sierra Match King Moly Coated 69 grain bullets is only 93% of maximum for IMR 8208 XBR. Many of my other best combinations of bullets and powders are significantly less than max.

I measure my charge load on a Gem Pro 250, which I think has a precision advertized to be .002gr. I'd have to dig up the literature to be sure, but it's pretty good. Sometimes I weigh each charge and sometimes I calibrate my Lock N Load PD on my progressive press and let it fill the cases. My typical charge weight extreme spread using the auto powder dispenser is less than +/- 0.1gr with a charge weight SD of around .06 depending on the powder type and shape.

 

[memilanuk]

I may be wrong here, but throwing all the data together like that makes it pretty much meaningless, in my opinion.

To begin with, your individual sample sizes are (relatively) small - only five rounds. The standard error of the mean (SEM) or the confidence interval (take your pick) is going to be relatively large, to the point where there isn't a meaningful way to differentiate between one group with an SD of 10 from another with an SD of 15, or possibly even 20. Then it sounds like there is a hodge-podge of different loads all being tested under different conditions, likely exacerbated by session-to-session variations in instrument setup, ambient conditions, etc.

I applaud your efforts for taking the time to collect all this data, and maybe there is a way to slice it into smaller batches that are at least comparing apples to apples, but as is... I don't think you're going to get anywhere with it like this.

Out of curiosity... what kind of chrono are you using, and how are going about setting it up? Have you read the chrono chapter of Litz's book 'Modern Advancements for Long Range Shooting'? (available as a stand-alone article here) It discusses a lot of things that can go wrong when using a chronograph...

 

[amlevin]

I may be wrong here, but throwing all the data together like that makes it pretty much meaningless, in my opinion.

To begin with, your individual sample sizes are (relatively) small - only five rounds. The standard error of the mean (SEM) or the confidence interval (take your pick) is going to be relatively large, to the point where there isn't a meaningful way to differentiate between one group with an SD of 10 from another with an SD of 15, or possibly even 20. Then it sounds like there is a hodge-podge of different loads all being tested under different conditions, likely exacerbated by session-to-session variations in instrument setup, ambient conditions, etc.

I applaud your efforts for taking the time to collect all this data, and maybe there is a way to slice it into smaller batches that are at least comparing apples to apples, but as is... I don't think you're going to get anywhere with it like this.

Out of curiosity... what kind of chrono are you using, and how are going about setting it up? Have you read the chrono chapter of Litz's book 'Modern Advancements for Long Range Shooting'? (available as a stand-alone article here) It discusses a lot of things that can go wrong when using a chronograph...

I agree. How much of your ES/SD is caused by the optical sensors just "triggering" off a different portion of the bullet "shadow" as it passes over. Unless you have a Looooooong sensor support there's far too much room for error in the typical 18" OAL chronograph, especially with higher speed loads.

I think this is why there are so many Oehler fans out there with their "six to eight footers".

 

[CharlieNC]

Recent load development on a new 223 shows a highly significant negative correlation between chrono es and group size, that is more rd gave tighter groups. Reason being the node tuning is associated with optimizing the barrel harmonic response which I judge at 200 yards, and it is affected minimally by velocity variability. On the other hand this is clearly not the case at longer ranges where velocity differences play a major role in verticle performance. Both components are necessary as distance increases.