SD for a 22 shot string

L

Lee FCLR

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I was doing some chrono work on the weekend just gone and after a 22 shot string the stats showed a gradual climb in speed which i put down to the barrel heating up over the course of the string. The SD came in at 13.8 which seemed high to me. Am I right in thinking that is high or should i expect that type of sd for a string of shots that long. Still new to chrono work so just trying to get a bench mark I know lots say single figures are good but is that for a string of twelve shots which is limiting the heat in the barrel or should the sd still be under ten for a longer string?:confused:

 
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What did the target look like ?
Chrono data must be used with the target,
not independent of it.
 
CMaier said:
What did the target look like ?
Chrono data must be used with the target,
not independent of it.
Click to expand...

HI,
the target was not too bad the majority of the rounds were centered as far as horizontal spread goes. The vertical spread was peppering the 6 and x rings with the occasional ( shot 11,18 and 21) high into the 5 ring and with a quarter minute adjustment on the fourth shot to move the group up slightly. The first two were from a cold bore but the barrel was fowled from a previous string of ten 12 shots. The main thing I guess I am looking to do is to minimize the vertical spread to tighten the group. This is the first time I have really used a chrono and had results that I can study, any other time I have used them was to get an average speed of the MV and only ever done over a few shots.

I have just bought this one and am just learning how to read data from it and make changes to my loading to tighten groups. So any input would be much appreciated. from what I have been reading around the traps ideally I would like to get my vertical spread to around 6(lower if possible) which would have the rifle shooting the x ring with the controller of the rifle being me the only failing factor when a round drops outside.
 
Bullet speeds

I would try to get the es numbers down..... what are you weighing powder on.........????
bil
 
It is my suggestion that you leave your chronograph at home and take your reloading equipment to the range next time. You will be able to make huge strides in finding a load that makes the gun happy - not to mention saving a huge amount of time. In my experience, fine tuning is where the chronograph comes in handy, and for final data storage of that particular 'happy' load. Your current situation is realizing poor accuracy - your time at the reloading table on the range will allow you to reap huge benefits.

Good luck!

Matt
 
trying to make decisions off a 22 shot string that is not a small group
is a waste of time, worry about chrono data when you have good loads,
not before.
 
Plot velocity versus shot number - that's a run chart. If you do this on Excel, the program can fit a line to the data and the slope, and how the values deviate from the line, can tell you something about what's happening. I've found that the cold shot tends to have lower velocity than average - the plot will highlight this. Plotting the run chart without the cold shot tends to produce a flatter line. And lower SD as well.

A SD in the low teens would be OK for some situations, not great for others. We've found that SD can be affected by charging method with some powders and in some cartridges. Repeating the test you did using "thrown" versus measured charges may be interesting. I have found that with some combinations, there is "no" difference. Other comparisons have driven me to individually weighing charges. Also, some bullets are associated with higher or lower SD, which may be indicative of bullet uniformity or fit to your barrel.

Of course, SD is not the absolute tell-all for accuracy/precision, but it is reasonable that, all things being equal, lower SD is better than higher.
 
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