ihmsa forums

No, not a gun this time. A Chrony chronograph...the Gamma Master to be exact.

I took it to the range today to test it out. I played with it the other day in the back yard shooting pellets through it, so I have an idea of how it runs. My question is:

How do I interpret the results? Here's an example from my .243 load...

Date: 20-Apr-11
ES % of Max Spd 3.5%
ES % of Ave Spd 3.6%
SD % of Max Spd 1.1%
SD % of Ave Spd 1.1%

Fastest 2331.0
Slowest 2248.7
Avg Speed 2267.3
Extreme Spread 82.3
Std Deviation 25.4
Average Deviation 19.0

Group 1
Shot 1 2331.0
Shot 2 2248.7
Shot 3 2298.3
Shot 4 2264.7
Shot 5 2253.3
Shot 6 2252.5
Shot 7 2265.2
Shot 8 2251.3
Shot 9 2249.2
Shot 10 2258.4

What I read from this is:

1. With my average speed well below 2300fps, I can bump it up a grain or two. As long as I stay under 2600fps, I should be fine...

2. I have no clue what to do with the ES and deviation data... Is 3% of the average speed good or bad?

This load seems accurate enough. I shot it last month at Lincolnton for the first time (UASBB and UASHS) and will shoot it again this weekend.

If this were your load, would you tweak it?

What do I need to start looking for in my testing?

Is there a good book out there that explains this? I've got a lot of reloading manuals, but I didn't really see much about load development...maybe I looked in the wrong book...


Thanks in advance for any and all help... I can always count on you guys to tell me where to go...


Chris

The extreme spread is just the difference between your highest and lowest velocities. The standard deviation is a statistical calculation based on all the factors. High, low, number of shots fired etc that give you the variation from the average. Low SD's mean more consistant loads.
Bret

I noticed that your first shot was the fastest. Is it possible that the barrel had been cleaned and still had some oil in it?

Regards, Bill Barton

Thanks for the quick replies...

Bret, I understand what the numbers are but I don't know how to interpret them. Is a SD of 30 acceptable, or do I need to try for 15?

Bill, yes and no... I don't think oil was a factor because my first shot of the second string was even faster. Here's my second string...(I only shot two strings)

Fastest 2373.5
Slowest 2253.3
Avg Speed 2314.7
Extreme Spread 120.2
Std Deviation 32.1
Average Deviation 26.4

Group 2
Shot 1 2373.5
Shot 2 2253.3
Shot 3 2306.6
Shot 4 2297.8
Shot 5 2304.8
Shot 6 2290.4
Shot 7 2344.1
Shot 8 2330.6
Shot 9 2303.5
Shot 10 2342.7


Chris

Personally I like to shoot (pun intended) for SD's in the single digits but even in the low to mid teens is good. 30 to me would be unacceptable. It is statistics though meaning an extreme spread of 100 on a round doing around 3800fps would give lower standard deviations than a extreme spread of 100 on a round doing only 800fps.
Bret

i agree with bret. i would try some more loads to get the es and sd down a bit. allen

Chris, as discussed, a low ES means you have consistent velocities. In a rough calculation you will find that SD is approximately 1/3rd of ES. If you have good numbers and lack accuracy there is likely another cause for the innacuracy. You can find loads that pring well on paper but dont have the small SDs. If you have good numbers and good groups you are likely onto something. rp

Thanks Richard. I had doubts about it after reading this thread, but decided to use it in the last Little River match. After my own screw-ups, it's not going to be long before I'm INT in both BB-UAS and 1/2 Scale... In UAS, I knocked down 40 targets (too bad one of them was Robert's... ) and in 1/2 scale, I didn't trust my scope. I have new sight settings now and will reattack this month.

So let me see if I understand you. If SD is less than 1/3 of ES, that's good right?

(Congrats on winning several categories in the GA SB/FR Regionals!)


Chris

As a general observation: SD is approximately 1/3 of ES. See your first set of numbers; es was 80, sd was 25. 80 is ''close enough to 75'' and sd is 1/3 of 75----25. It's just a rough look at ES and a quick mental calculation of SD. If ES was 100, SD would fall around 33. rp

If you're just looking at the SD's, the lowest ones would be better and SHOULD shoot better, however, I have found one thing that I pay attention to. Compare the SD's to the groups on paper...sometimes a load with a much higher SD just shoots really well. I have no explanation why, but one of my Dan Wesson revolvers loves a particular load that gives an SD of about 80. Ideally, the lowest SD's will show the best groups, just watch out for that anomaly.