ES and SD

[Russ Hatch]

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]

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]

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

 

[Russ Hatch]

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]

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]

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]

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?

 

[milanuk]

Really. You mean all those matches I shot 2 sighters in were figments of my imagination?

There is more than one flavor of long range competition... some get a fixed time period for unlimited sighters, some get a fixed amount of time for unlimited sighters *and* all their record shots, some get a fixed number of sighters, and some get a fixed number of sighters but can convert those sighters for record score if they want. Being one of those that likes the 'fullbore' style matches with convertible sighters... what my first and second shot is just as, if not more so, important to me than what the last ones do.

And yes, it is relevant. The larger your sample size, the better it simulates the total population - i.e. any given shot you might fire any given day, whether the 10th shot in a string or the 1st. That said... reality being what it is, the economics of running large numbers of shots across the chrono simply for the sake of data gathering starts losing its appeal with the larger wunder-boomer / barrel-eater calibers.

Generally speaking... you're probably safe just taking your average MV and your ES and going from there - 18 shots isn't a bad sample size. Could be better (bigger) but the real world is rarely ideal. If you wanted to be a bit more thorough, take +/- 2SD (i.e. +/- 29fps, or ES=58) and that should give you roughly 95% of all the shots you'll fire with that load from your gun - in theory. If you're paranoid take +/- 3SD (+/- 43.5fps) and that should cover 99.7%. As your sample size (# of shots in the string goes up, your observed ES and the theoretical ES (+/-3SD) should get closer and closer together. Most of the very small ES/SD numbers you see mentioned on the Internet don't hold up when the sample size increases to 20 or 30 - 30 being a somewhat 'magical' point where statisticians traditionally draw the line between 'small' samples and 'large' samples.

Seeing as most of us have better things to do than fire such large shot strings, and as Mike pointed out, the accuracy and repeatability of most consumer grade chronos is somewhat questionable - how do you, the purchaser, go about testing them in a repeatable fashion? You literally can't use the same powder charge, primer or bullet; the only thing you can do is reload the same case over and over but thats not really the same for testing/verification purposes. At some point you have to accept this data as simply being a 'good guess' and 'close enough'. Take the gun out and shoot it at as far of a distance as you can find. If it holds vertical at distance, what the chrono says doesn't matter that much anymore.

 

[Mikecr]

There is absolutely no relevance between competition and hunting.
There are NO sighters, NO fouling, NO warming the barrel, or windflags, or Bench, or stool, or rest, or 17lb gun, or martini(shaken -not stirred) -in HUNTING.
Stretching to make connections between these two shooting applications is a waste of resources.

He'll have to allow the barrel to completely cool between shots, before he can determine anything about his cold barrel ES.
Russ, just note the chrono readings between your first cold barrel shot and the second and third warm shots to follow in 'group' shooting. Don't cheat..
You notice that 100fps ES?
That ain't gonna get it for hunting, anymore than it does for competition.

That's 3 shots to dissolve any delusions, and decide what you need; That first shot,, or that last shot.

 

[milanuk]

Mike,

Must be the (recent) full moon or something... I'm feeling more argumentative than usual - so please take it with a grain of salt

My form of long-range competition doesn't involve a bench, a stool, or even a front rest necessarily. Wind flags lie like a... well you get the idea I'm quite happy off a bipod and a rear bean bag.

gun)

I will take the 17lb (18 actually) gun, though

Not all long range hunting is on big game... chasing sage rats and ground squirrels at distance is my idea of fun. Dang small targets and yes, lots of barrel heat. 'Sighters' too, if you count bouncing one off the mound and then 'splashing' the next one...

At any rate, I do agree, for most other types of hunting, the first shot is the one that needs the most attention. It'd be a massive PITA to do, but going to the range and setting up for a cold-bore shot at something like 200-300yds (where you can't just stack 'em one on top of another as easily) through a chrono over several separate range sessions might be informative... I'm just of the opinion that if you can't get the ES/SD down for 'regular' 5-10-15-20 shot strings, where the barrel does heat up and foul a little... you might still have some work to do before focusing in on the cold bore shot. Obviously, opinions vary...

Take care, and please don't take the above too seriously

Monte

 

[Russ Hatch]

"Russ, just note the chrono readings between your first cold barrel shot and the second and third warm shots to follow in 'group' shooting. Don't cheat..
You notice that 100fps ES? "

String 9
1) 2427.0
2) 2392.0
3) 2413.0
High: 2427.0
Low: 2392.0
E.S.: 35.0
Ave.: 2410.7
S.D.: 17.6
String 10
1) 2428.0
2) 2399.0
3) 2411.0
High: 2428.0
Low: 2399.0
E.S.: 29.0
Ave.: 2412.7
S.D.: 14.6
Guess I have some work to do. These two strings were from my rifle the oter 8 strings were rom my buddies rifle. Not 100 fps difference in three shots but not good enough. Did not mean to start arguement just curious what other people use as a sample.
Russ

 

[Mikecr]

Russ, are you saying these shots:
1) 2427.0
2) 2392.0
3) 2413.0
began with a cold barrel,, or a prewarmed barrel?
And how long was it between shots?

I ask because it is common that these shots from cold, would climb considerably in velocity, and I've never seen contradiction to it.

Nobody's arguing Russ. It's a respectful discussion with contrasting views.

 

[Russ Hatch]

Cod barrel on the first shot of string 9 and then waited until the barrel did not feel hot to my hand on each of the other shots. I have shot three shot groups without waiting for the barrel to cool down with the following results.
String 2
1) 2460.0
2) 2457.0
3) 2427.0
4) 2434.0
5) 2421.0
6) 2451.0
High: 2460.0
Low: 2421.0
E.S.: 39.0
Ave.: 2441.7
S.D.: 16.5
String 3
1) 2428.0
2) 2444.0
3) 2420.0
High: 2444.0
Low: 2420.0
E.S.: 24.0
Ave.: 2430.7
S.D.: 12.2
String 4
1) 2424.0
2) 2437.0
3) 2425.0
4) 2423.0
5) 2432.0
6) 2444.0
High: 2444.0
Low: 2423.0
E.S.: 21.0
Ave.: 2430.8
S.D.: 8.4
I usualy shoot three shots and let the barrel cool. My rifle after three shots the barrel is very warm to the touch. As you can see I forgot to store the readouts after three shots in string 2 and string four, but they were three shot groups. String 1 was a buddies rifle.

 

[Mikecr]

Ok, good info
Discarding string 9 and focussing on normal first shot conditions from string 2;
String 2a 1st shot = 2460
String 2b 1st shot = 2434
String 3 1st shot = 2428
String 4a 1st shot = 2424
String 4b 1st shot = 2423

Looks **** good to me.
Especially if the 1st shot, string 2a, was fouling or truly a different barrel temp than the others. That 2460 obviously came from different conditions than the rest..
Consider the ES of 2b to 4b.....11fps!
All the rest of the shots taken meant nothing at all.

But to be sure you're sitting so well, try one shot per 2hrs or so, or one shot per day if more convienient, across the EXACT same chrono setup. This setup is important because 1/8" off changes a chrono reading near the muzzle A LOT.
To make more use of this, take each on a 1"dot 300yds out. Same target, undisturbed for every shot.
With enough of an ES sample to satisfy the statistician in you, measure the furthest bullet hole on target -to center of mark. This is your cold barrel accuracy -so far.
Then do the same off a bipod in the dirt for your cold barrel 'field accuracy', if appropriate to do so.

Sure, all this takes more time and work. And that's why it's not what everyone else is doing. But it isn't killing barrels or chasing your tail either. Each shot tells you more than 10 tell most people.