ES and SD

Russ Hatch · #1 11-05-2009, 08:12 PM

How large of a sample do you use for determining ES and SD, 5,10,15 or 20 rounds?
Today I fired 18 rounds through the cronograph and had an ES of 56 and a SD of 14.5. All shots fired at the same aiming point with a group size of less than an inch.
When looking at the read out from the Cronograph I noticed that the largest ES for three consecutive shots was 22 fps. So is this a good load or not?
Russ

WRG · #2 11-05-2009, 10:31 PM

There are a lot of things that can have an effect on your extreme spread. I think the most would be how hot the barrel gets during firing. The way I do it is I use a 5 shot group during my work ups. After the first 5 rounds I let the barrel cool completely down before firing the next set. This is because I want all variables to see the same conditions if I'm doing a ladder work up. Even before I start the first set I will fire 2 to 3 fouling rounds before I start the work up because my barrel is clean before I start.

Now if all my rounds were the same I would still do a 5 set shot then cool the barrel. Then I'll compare the ES of each set. I think this gives a more accurate result as to how the round is performing. All my rounds are typically for a hunting application and not compitition so if I saw an ES of 22 fps that would be concidered exceptable. Now if I was setting up for compitition I would be looking for something under 10 fps and aiming for 5 fps or under.

If you want to bring down that 22 fps, how maticulous you are with your case prep will help. Of course trying other powders, primers, bullet seating depth and a list of other things will help with that also but, for a hunting application that would be fine as long as your happy with the accuracy. If you had a 56 in a 5 shot group I would be concerned!

Mikecr · #3 11-06-2009, 06:31 PM

Russ, have you taken your chronograph's accuracy into account?
And do you generally take 18 shots at game?

Russ Hatch · #4 11-06-2009, 08:09 PM

Mikecr,
Nope and nope. I have two cronographs and have not run them in tandem yet to compare them. Usually one shot and DRT I ambush hunt form a tall tree. Next time at the range I'll try the tandem crono set up. I have read at various shooting resources that the larger the sample the better the comparision results. Thought I would try 18 shots through the crono and then got to wondering what other people thought a good sampe was.
Russ

Winchester 69 · #5 11-07-2009, 04:08 AM

Isn't this a fine way of torturing yourself? After you've determined which shots are totally random (3SD < ES), then you can decide how it all correlates to vertical dispersion. Of course, if you weren't computerized you wouldn't be worried about it.

bigbuck · #6 11-07-2009, 11:46 AM

From what I've read those that compete @ 1000 gather this information by 10 shot strings if it's good with a 10 shot string then it's good to go.
That's shoot 2 fawler shots and then chrono the 10.
Bigbuck

Mikecr · #7 11-07-2009, 12:50 PM

BigBuck, it ain't 2 foulers that competitors get. It's 2minutes of sighters to fixed distance -pit marked targets, over windflags, with extremely heavy guns, off benchrests. This can foul, but certainly gets their barrels to stable temps.
Big factors in ES, and POI consistency..

Did you read also that hunters don't get any of this, and that none of it applies?