Standard deviation.

[NF1E]

As of late, I have been loading .223 ammunition for precision shooting. Never paid any particular attention to SD. Well, over the last couple of weeks I have been doing a bit of checking on the results of differing variables. Powder is loaded to within .02 gn which is the size of a kernal.  Bullets used are Berger 73 gn bt target and have not  been sorted by weight. Primers are BR-4s and I have been told that other primers should lower the SD even more. I did not notice any measurable difference in point of impact at 100 yds. Each group tested was 50 rnds, or 1 of my range boxes. Thought some might be interested in those variables.

New Starline .223 50 cases sized and loaded with 23.5 gn of Varget.  SD 20+
    "       "               "    50  cases  sized, and weight sorted to 1 gn with 23.5 gn Varget.   SD 12+
    "       "               "    50  cases sized, weight sorted to 1 gn with flash hole de-burred loaded with 23.5 gn of Varget   SD 6.5+


Whatta Hobby!

[Albroswift]

Flash hole deburring tool is one of the best "Bang for the Buck" reloading tools out there. Rifle I like to see 10 or less, 5 or less is outstanding. Your last line is looking good. There are arguments on whether (and how) a low SD relates to a tight group, but the way I see it it can't hurt and is good feedback on the quality of the handload. Next step is neck turning. 

  

338 WinMag 185 Barns

 

405 WCF 300gr Hornady Interlock

 

Edited May 21, 2024 by Albroswift

[NF1E]

Very nice indeed. Used to neck turn when I was a bit more picky than I am these days. Now with Laupa or Starline I just neck size, run a tapered carbide mandrel down the tube and call er done. My Labradar always has shown a much better SD than that calculated from results of an optical chronograph as used in this informative example. Whatta Hobby!

 

 

 

[Cunuckgaucho]

So when you sort your cases do you pick a specific weight and use that for all your precision shooting and regulate the rest as plinking ammo?

Or do you just put together 50 case lots where each lot is within 1 grain but no two lots are necessarily the same?

[Albroswift]

In the larger calibers, huge volume swing between brands. Amounting to 80-90 FPS in the 300 Weatherby between Weatherby brass and R-P Brass with identical charges. With my 338, I've had it so long that my brass is all over the place. Trying to keep batches together, have a Redding die that controls length and have a Dillon trimmer for the 650 when they get way out of control.  

[NF1E]

On 5/22/2024 at 12:47 AM, Cunuckgaucho said:

So when you sort your cases do you pick a specific weight and use that for all your precision shooting and regulate the rest as plinking ammo?

Or do you just put together 50 case lots where each lot is within 1 grain but no two lots are necessarily the same?

 

With both Starline and Lapua brass the weight sorting is pretty simple, most is within 3 -4 gn so that breaks down to 3 divisions of 1 gn each. I keep these groups separated into either 50 or 100 count range boxes. No such thing as plinking around here anymore. Whatta Hobby!

[Cunuckgaucho]

Thanks,

 Just wondering if you notice a change in POI between the divisions? if any how much?

Also do you get a measurable difference in the muzzle velocity between the divisions?

Edited May 24, 2024 by Cunuckgaucho

[NF1E]

Haven't paid much attention as to variations in poi between sorted cases. I tend to take a 50 cnt range box of segregated ammo out , fire 5 sighters/foulers and then enjoy the shooting. I must say, I have not changed my scope settings more than a click or two vertical.  Not sure if it's weather or ammo related. Again, not looking for differences in velocity between groups. Maintaining consistency withing each group has been my goal. Use of a barrel cooler between shots has seemed to help too.  Whatta Hobby!

 

 

[Cunuckgaucho]

Barrel cooler, interesting.

Makes me think I should bring an infared thermometer to the fall shoot, take readings as we shoot. Between the IR thermometer and the chrono and changes down range it would be interesting to see if there is a useable pattern

[NF1E]

I use the cooler between strings mainly to help reduce mirage and secondly to , hopefully, help extend the life of my barrels. Whatta Hobby!

 

 

[98Z5V]

On 5/24/2024 at 8:11 PM, Cunuckgaucho said:

Barrel cooler, interesting.

Makes me think I should bring an infared thermometer to the fall shoot,

@JBMatt has a barrel cooler, and I've got an IR temp gun that I use for work, brother.  Don't worry about bringing any of that for the Fall Shoot - we already have it.  Pack Light...    We got you, no questions asked...  

EDIT - And now, we have TWO Garmin chronos to use, so we're covered on that part, as well. 

Edited June 5, 2024 by 98Z5V

[Cunuckgaucho]

I figured if I mentioned it something would turn up 

As to the barrel cooler, well I have me a new 3D printer(16"x16"x 19"H work envelope) That I'll unpack( still new in box) and knock off a few to bring down for the fall.

https://www.thingiverse.com/thing:5351868 the site also has a bunch of files for reloading/shooting accessories. Once I get going I'll start a thread on #D shooting related stuff

[JBMatt]

I got tagged here, so here's my .02 cents on this stuff from my experience. Lol

SD's are only important the further out you're planning on shooting.  I've had horrible SD's make little tiny groups at 100.  I've had low single digit SD's pattern like a shotgun at 100.  That gets addressed by changing seating depth.  I always chase SD's and intended velocity first.  If I can't get an acceptable group with both of those factors being what I want, I change bullets.  Looking for mid/low single digit SD's on a bolt gun and anything less that 12 in a gasser is good enough.  Obviously lower is better.

Primers make a huge difference on SD's AND velocities.  Just a primer change can either help or hurt an otherwise good recipe.  Finding the right one is just part of the process.  Just because it's a BR Primer doesn't mean it's necessarily going to work.  I've been surprised before.  Neck tension and shoulder bump are also very important, in my experience.  Case weight variation doesn't seem to really matter so much but different brands/lots do. Neither does concentricity if you're using quality loading  equipment.  Bullet sorting by BTO seems to be the only real factor that makes a noticeable difference down range being that it has the most effect on BC consistency.

Barrel coolers and a temperature strip on the barrel or laser thermometer are a must have for keeping the testing consistent.  All the data you gather doesn't mean anything if the barrel temp is different for every string of shots.  I made a barrel cooler out of an old ice chest that I installed an air mattress pump in and use freezer packs in it to draw cold air instead of ambient temperature.  A must have here in the desert.

I'm probably preaching to the choir, but it sounds like you're on the right track.  I've found that some of this stuff that one think's should make a difference, doesn't really.

And I agree!  Whatta hobby!

[Magwa]

Indeed.... The biggest contributor to a low SD for me has been consistent neck tension and shooting on the right powder node charge I also full length size each time and aneal each time I bump my shoulder each time by 2 thousands and I use Lapua brass only and have found no need to deburr flash hole or primer pockets I also do not weigh cases just shoot same lot and keep track of round count. I never clean my brass found it made no difference and I do NOT clean my gun unless accuracy starts to fall off around 140 to 170 rounds. the best thing for neck tension is the use of a expander mandrel to set my neck tension at 2 Kthat spelled the difference in SD for me . and I never turn necks..... that for my shooting produces S.D in single digits and loads that shoot well from 100 yards to 1 mile consistantly.

   Here is a example the barrel had 112 rounds through it and shot a 1/2 inch group with these speeds

cold bore 2968

                 2970

                 2966

                2966

                 2966

                 2975       S.D 3.6    it works..

Edited September 14, 2024 by Magwa