Question about extreme spread or deviation

[rcoodyar15]

Ok I got my croney working today.

Shooting MK 69 gr. my best 10 shot string had an average velocity of 2729 extreme spread of 30 and a deviation of 13.78

Is that about average?

Now my worst string had an extreme spread of 50.

I don't know if it was my shooting or the deviation but my best group had the lowest deviation.

I am trying to get consistent 1/2" groups at 100 yd

What causes the difference in velocity? I know variation in powder charge, neck tension, case volume and probably others

But what is the major one? If you picked out cases with near the same velocities would that help? or are they just as likely to have a different velocity next time.

Probably just overanalyzing this thing but that is what I do. I am an engineer and unfortunately I am tormented by the grey.

[bigedp51]

What type rifle, caliber and powder are you using?

[rcoodyar15]

What type rifle, caliber and powder are you using?


homemade AR15, match grade .223 wilde barrel, these loads were CFE223

[T2C]

What causes the difference in velocity? I know variation in powder charge, neck tension, case volume and probably others

But what is the major one? If you picked out cases with near the same velocities would that help? or are they just as likely to have a different velocity next time.


You are on the right track. If you sorted your cases by manufacturer and year, it might make a difference. Some of the bench rest shooters measure case volume with alcohol and sort them accordingly.

You bring up a good point about neck tension. I normally don't crimp rifle reloads for target shooting, but I have had a few loads that were more consistent/accurate with a slight crimp.

I believe that primers have an effect on consistency of velocity, and only the company who made them has control over quality.

The position of the powder charge inside the case could make a difference. Is your powder charge filling most of the case between the primer flash hole and the projectile? Changing to a lower density powder and dropping a charge weight that fills more of the case and gives the same muzzle velocity may make a difference.

As the barrel warms up, it could have an effect on the extreme spread and standard deviation with a good load. Personally I have noticed a difference in ES and SD readings when testing the same ammunition in a bolt action rifle.

The bottom line is that how a rifle groups on paper is the best indicator of a good reload recipe. ES and SD numbers can steer you toward a consistent load, but that is only one factor in the equation. I have had reloads with low ES and SD that did not shoot well. I have also had reloads with large ES and SD numbers that shot really well.

With a 1:8 twist barrel and 75g projectiles, 10 shot 1/2" groups at 100 yards is doable with an AR-15.

[rcoodyar15]

Using all lapua brass out of the same lot. Haven't sorted by weight yet but that is probably coming.

primers are CCI br-2

going to try a couple of more powders before I decide on a load

Just ordered a lead sled FCX to eliminate all human error during load development.

[bigedp51]

You are using a double base ball powder that has more deterrent coatings than single base powders which makes it harder to ignite. I use Remington 7 1/2 primers in my AR15 loads with ball powder, Remington ran Lake City from 1941 till 1985 and used the 7 1/2 primer to light off Winchester ball powders. Bottom line the Remington 7 1/2 primer was adapted for the M16 rifle requirements and using ball powder and it is not called a magnum primer.

http://i122.photobucket.com/albums/o254/bigedp51/3CCIBR4_zps20b88c85.jpg

http://i122.photobucket.com/albums/o254/bigedp51/5Remington75_zps2b532d7c.jpg

And when reloading for your AR15 and using ball powder you should listen to the 1967 song by The Doors "Light My Fire" :smile: It was also a good year for gallon jugs of Bali Hi wine :alcoholic: and M16s that jammed. :angry:

[J-cat]

A SD of 13 isn't bad, but you should try a magnum primer with the CFE. To cut down ES some more, sort the cases by weight in 1gr lots.

[markm]

You are on the right track. If you sorted your cases by manufacturer and year, it might make a difference. Some of the bench rest shooters measure case volume with alcohol and sort them accordingly.

I've found this to be a complete waste of time for sane (non benchrest) match ammo. In fact... our worst groups are always when we pick out the same flavor of brass. It's nuts, but it never fails.


You bring up a good point about neck tension. I normally don't crimp rifle reloads for target shooting, but I have had a few loads that were more consistent/accurate with a slight crimp.

My ammo's group sizes were cut in less than half with a light factory crimp. I posted the results months back. I didn't expect it to make a difference, but the crimp really must even out neck tension.


I believe that primers have an effect on consistency of velocity, and only the company who made them has control over quality.

Primers are a huge piece of it. I specifically don't shoot ball powder because the Russian primers don't work good with some of the Ball powders.