what does S.D. mean in this context?

[Big Chudungus]

(they are talking about Tika Arctic bolt action 308)

We clocked and grouped three types of rounds. First up, Remington Premier Match 168-grain Matchking BTHP ran at 2,487 fps, with an eye-twitching S.D. of 37.2. Next up, Hornady’s Precision Hunter 178-grain ELD X ran at 2,488 fps, with a very respectable S.D. of 12.3.

[Fjold]

Standard deviation - How much variance in velocity of each shot. The lower the value of the SD, the more consistent your velocities are and usually the more accurate they they will be. With one of my match loads a difference in velocity of 100 fps at the muzzle will result in a difference of a 8" in elevation at 1,000 yards.

It's basically the average difference from the average velocity of a string of shots. You can find the complete formula on line. Many chronographs have the ability to calculate the SD and give you the result from each shot string.

[Big Chudungus]

thx, when he said "eye-watering" I thought maybe it was muzzle-blast/fire-ball face concussion. lol.

[smoothy8500]

(they are talking about Tika Arctic bolt action 308)

eye-twitching S.D. of 37.2..........with a very respectable S.D. of 12.3.

In the grand scheme of things, the difference between 12 and 37 is really not that big a deal.

[Experimentalist]

In the grand scheme of things, the difference between 12 and 37 is really not that big a deal.

Depends on application. For hunting, plinking, etc. you're correct.

For precision rifle use hand-loaders strive for single digit Standard Deviations.

[Fjold]

In the grand scheme of things, the difference between 12 and 37 is really not that big a deal.

Standard Deviation is the square root of the difference.

If you had a ten-shot group with a mean (middle value) of 2754 fps and an extreme spread of 16 fps, you would have a Standard Deviation of 5.5 fps (very good)

The same size sample group at the same mean (2,754 fps) with an extreme spread of 37 fps, would get you a SD of 9.5 fps (still good)

The same size sample at a mean of 2,754 with an extreme spread of 53 fps gives you a standard deviation of 13.1 fps (still OK)

If you have a Standard Deviation of 37 fps, then you are talking about extreme spreads of more than a couple of hundred fps. (terrible). You would see noticeable vertical stringing at distance.

[smoothy8500]

With one of my match loads a difference in velocity of 100 fps at the muzzle will result in a difference of a 8" in elevation at 1,000 yards.....
You would see noticeable vertical stringing at distance.

Yes, we strive for lower velocity spread. It is true that there will be influence on vertical stringing. But, 95% of the rounds will be within 4 SD's; 148fps

As evident by your example, a little over one (1) MOA at 1,000 yds.....

Well within most shooter's margin of error at 1K, and not really that big of a deal at 600.

[Scotty]

68% of the rounds will be +/- one SD from the average. 95% will be +/- two SD from the average.

[W.R.Buchanan]

OK: Changes in Velocity equal Changes in Trajectory. Changes in Trajectory equal changes in Elevation at the Point of Impact. Obviously that means changes in group size at your given Range.

I have a friend who is a high end Bench Rest shooter. he recently shot a 5 shot group at 1000 yards that measured .968" his SD for that load was 1.4 !!!

At my level of shooting an SD of <40 would be fantastic and no gun that I own would shoot better than that, and I could not shoot better than that, and neither could 95% of the shooters out there.

Something to consider ? But not necessarily overlook?

Randy

[Fjold]

If you have 2 MOA eyes, a 2 MOA gun and 2 MOA of standard deviation, you have a gun that will shoot 6" groups at 100 yards.

[Markbsae]

I have a friend who is a high end Bench Rest shooter. he recently shot a 5 shot group at 1000 yards that measured .968" his SD for that load was 1.4 !!!

Randy

that's insane!

[W.R.Buchanan]

that's insane!

I saw the Target! I was blown away.

Randy