What is ES ???

[mrbeer]

Hello All...I seem to be asking a lot of questions these days as I am Just getting hooked with the whole BR world.

I just got to shoot at 1000 yards for the first time last week and I am hooked. I was shooting my .308, but some guys at my local club let me fire a few rounds down range in their 6BR rifles....and well... I'm hooked.

I often see BR shooters refer to their "ES" which I assume to mean "extreme spread"... a common statistical term often used in conjunction with standard deviation. Is this term usually used to refer to spread in projectile VELOCITY or in GROUP SIZE? Shooters are always trying to reduce their ES.

What is everyone talking about with ES?

 

[Moderator]

Most of the time ES and SD refer to Extreme Spread and Standard deviation of shot velocity measured over a chronograph.

However, some 1000-yard shooters use ES to describe group size, but more particularly vertical shot dispersion of a group (5 shots or 10 shots). These guys try to build ammo that has minimal vertical dispersion under perfect conditions. At 1000 yards, vertical dispersion is affected by many variables, including shot-to-shot muzzle velocity variances, bullet-to-bullet BC variances, and of course, wind, temperature, mirage etc.

Some of the top Dasher shooters in Montana are achieving close to 2" vertical dispersion for 5 shots at 1K in perfect conditions. That translates to roughly 0.2 MOA. That's getting very close to the mechanical accuracy of the gun at 100 yards in a tunnel.

 

[mrbeer]

Are there any down sides to Dasher vs. standard 6mmBR. I am thinking of building a BR rifle for 600-1000 yds as well as f-class. I have pretty much narrowed it down to 6BR and dasher.

What would the pros and cons be to each round?

 

[TerryPohl]

The only down side to the Dasher is fire forming brass. Look on the front page of this sight and it will give information on how to do it.
I have two Dashers; I use the false shoulder and the COW method. At the range you said you would like to shoot the Dasher I think would be the way to go. I love both of mine.
Terry Pohl

 

[Laurie]

Some of the top Dasher shooters in Montana are achieving close to 2" vertical dispersion for 5 shots at 1K in perfect conditions. That translates to roughly 0.2 MOA. That's getting very close to the mechanical accuracy of the gun at 100 yards in a tunnel.

That really is astonishing. Sooner or later somebody shooting such a rig on such a range will have all the variables work in his or her favour and a large chunk of luck thrown in, and then there will be such a small group that it'll be virtually impossible to better it!

 

[243Mendoza]

a better measure of dispersion than ES is sigma; you can use a multiple of sigma to determine the tightness of the dispersion

 

[Moderator]

Rich made a good point about bullet selection. My 6BR has about an .080 freebore and I can shoot anything from the 60gr FB to the 108s. With the 95gr VLDs I have just about the minimal shank in the neck to be .012" in the lands.

On the flip side, a Dasher can launch the 105s and 108s at 3030 fps without much difficulty... in most barrels. With the same barrel, a standard 6BR case will deliver max velocities of 2850 to 2940 or so (depending on barrel). Yes some guys have topped 2960 fps with a std 6BR, but for every one of those there are three guys who can't get much more than 2850 -- particularly in the Savage factory barrels.

My 6BR load is 30.3 Varget with 105gr Scenars at 2910-2920 (depending on temps). With a Dasher I'd run the same bullets 120 fps faster. Interestingly we recently tested the 95gr VLD. It shoots incredibly accurately (in the ones at 200 yards) at 3060 fps with 31.3 Varget. That gives you near-Dasher performance without the hassle.

 

[dreever]

I have two 6BR's both with 26 inch Kreiger .237 bore .269 neck chambers. Both chambered with my own reamer, so the spec's are identical. Using the exact same load which works very well in both, (Berger 105 VLD's) one gives me 2940 fps the second one only 2850 fps. Why? I have no idea. That's just the way it is.
Each barrel is different. Sometimes you get one that gives you a lot of velocity, sometimes you don't. It's the luck of the draw.

Danny