Es/sd

[Davecoff13]

What should be good for extreme spread/ standard deveation for 5.56/223 for an ar? Not bench shooting or any thing crazy just want range ammo with at least combat accuracy. 55 g fmjbt ammo 24g AR comp powder cci military primers.

[MJinPA]

10 good. 100 bad.
Since I’m not sure what problem you’re trying to solve or what es/sd you’re starting with I’m not sure what other advice to give.


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[Davecoff13]

Not really trying to solve a problem per say, but just curious how good people try to get AR ammo. I don’t have my load book here at home but I recall the sd to be in the 30s. I know pistol you work towards single digits. But being rifle velocities are in the 3000 FPS range vs 900 FPS range does that mean higher extreme spreads and a higher standard deviation is going to follow? As in if you have a pistol round that shoots 1000 FPS +/- 50 FPS that’s +/- 5 %.  And then you have a rifle round that shoots 3000 FPS +/- 150 FPS that is still +/- 5%. However you have a es of 300 vs 100 for the pistol round but the same percentage of velocity fluctuations. Hope that makes sense just curious. 

[MJinPA]

For rifle I’m normally 10-15 sd for stuff I put extra work into and 20-30 for the stuff I load in bulk. Typically 223 plinking ammo. For pistol I’m typically around 15 for sd. Single digits is pretty rare for me. Most of what I load is pistol ammo for uspsa and it’s plenty accurate for that.


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[pjb45]

Just some fundamentals on statistics:

1. Sample size matters!  Less than 35 is not useful.

2. Extreme Spread is interesting but not as important as SD

3. Standard Deviation is a great number

 

You might want to shoot for something like a 95% Confidence Interval.  

[donno]

FWIW-Below are one of my sets of results for my long range load. I usually test 5 sets of 5 (not sure why 4 here) and this is the avg. of the sets. This 24.0gr of 335 with a Hornady 75 BTHP. The Hornady Black, which is an accurate round in my rifles, had a SD of around 23. I'm sure my 55gr burner rounds have a higher SD as I pump them out at a much quicker rate.

 

Bullet Weight(gr): 75.00

Temp: 49 °F

BP: 1019.46 inHg

Altitude: 500.00

#          FPS  FT-LBS      PF

4    2734    1245.01  205.05 

3    2738    1248.66  205.35 

2    2728    1239.55  204.60 

1    2754    1263.29  206.55 

Average: 2738.5 FPS

SD: 11.1 FPS

Min: 2728 FPS

Max: 2754 FPS

Spread: 26 FPS

Shot/sec: 0.4

True MV: 2741 FPS

Group Size (in): 0.00

[milanuk]

7 hours ago, pjb45 said:

 

1. Sample size matters!  Less More than 35 10 is not useful practical.

 

 

FTFY

 

On a more serious note, while I do actually agree with you in a technical sense... running samples of >30 for each and every load increment does *not* make any kind of sense for people living in the real world.

For that matter... for someone like the OP, loading 55gn FMJ ammo for a .223 / 5.56... don't even worry about it.  Really really.

1. By the time you shoot that load far enough for the ES/SD to actually matter... that load is already sucking balls in the wind, general accuracy, etc.  Shoot it within its reasonable limits - I'd say 300yds, others might stretch to 400 - and its a non-issue, or at a minimum, the least of your worries.
2. For whatever reason, .223 Rem / 5.56 is notoriously difficult to get good ES/SD values from, even in match guns with precision handloads using good bullets matched with suitable powders and better primers.  Tight ES/SD is just not it's game.  I fought it when I shot Service Rifle / Match Rifle, I fought it (and still) do when shooting FTR at longer distances.  Not saying it can't be done, just than the general level of effort to get a .223 down to the same ES/SD numbers *consistently* as a .308 or any other mid-sized cartridge, is significantly more.

Edited September 15, 2020 by milanuk

[pjb45]

17 hours ago, milanuk said:

 

FTFY

 

On a more serious note, while I do actually agree with you in a technical sense... running samples of >30 for each and every load increment does *not* make any kind of sense for people living in the real world.

For that matter... for someone like the OP, loading 55gn FMJ ammo for a .223 / 5.56... don't even worry about it.  Really really.

1. By the time you shoot that load far enough for the ES/SD to actually matter... that load is already sucking balls in the wind, general accuracy, etc.  Shoot it within its reasonable limits - I'd say 300yds, others might stretch to 400 - and its a non-issue, or at a minimum, the least of your worries.
2. For whatever reason, .223 Rem / 5.56 is notoriously difficult to get good ES/SD values from, even in match guns with precision handloads using good bullets matched with suitable powders and better primers.  Tight ES/SD is just not it's game.  I fought it when I shot Service Rifle / Match Rifle, I fought it (and still) do when shooting FTR at longer distances.  Not saying it can't be done, just than the general level of effort to get a .223 down to the same ES/SD numbers *consistently* as a .308 or any other mid-sized cartridge, is significantly more.

I tend to normalize my data when I have arrived at a load I think is appropriate. 

My  Chrono allows me to download the data to a spreadsheet so the calculations are a POC. 

I calculate the dope with two different applications then set up targets next to each other at distances out to 500 meters to confirm the dope.  {I test two bullet weights at the same time}  

I have dope for X193, Hornady 68 gr, SMK 69gr, and S62 gr rounds for my Swaro.

Pretty anal for most 3Gunners and lackadaisical for the bench rest/precision rifle folks. 

[Jim Watson]

Agree with milanuk.  

The OP appears locked in to one hardball load, he is pretty well stuck with whatever spread that develops.  And it doesn't matter at hardball ranges.

When I tried to make a .223 into a FTR, I was happy to see SD/ES under 15/40.  I could do a little better with .308 but not a lot.    

On the other hand, my .40-65 BPCR could be gotten down to a SD of 3 and a ES of 9-11.  Very important with a big slow bullet at 500 m - 600 yd.