Es, SD and accuracy confusion.

Jmccracken1214

Gunny Sergeant
PX Member
Minuteman
Dec 10, 2018
931
343
Thomasville, NC
So far I haven’t had luck with my tikka 223. I’ve had some very small groups, but followed with a ES of 30-40 and a SD not much lower.

Lucked into some federal match primers and trying them... had this group shoot with an ES of 4 and SD 1.4..... but grouped like this: what gives?

D1042F9F-A6C0-4FC1-A0D3-5584F773A2B6.jpeg
 

pfl338

Luv2#Steel....
PX Member
Minuteman
May 16, 2020
180
186
Fort Worth TX
I believe you can have good ES SD and still get crummy groups, if all shooter error is taken out, it probably just that the rounds are not exiting the barrel at the ideal node for this particular load,( another words the barrel end is at a different point of vibration as each round exits instead of consistently at the same point) I am sure someone else here has a more detailed scientific explanation.
 
  • Like
Reactions: Dstoenner

Hoyt7mm

Bow Shooter
PX Member
PX Member
Minuteman
Apr 6, 2017
469
94
West Bend, Wisconsin
Play with seating depth to tighten up the group. Load up 3 rounds each with progressively longer jumps by .003 or .005" increments. You'll find a couple of groups that are nice and tight. Note the seating depth and load to the long side of that seating depth load.
Or
Pick a seating depth and buy a tuner
 

Jmccracken1214

Gunny Sergeant
PX Member
Minuteman
Dec 10, 2018
931
343
Thomasville, NC
Play with seating depth to tighten up the group. Load up 3 rounds each with progressively longer jumps by .003 or .005" increments. You'll find a couple of groups that are nice and tight. Note the seating depth and load to the long side of that seating depth load.
Or
Pick a seating depth and buy a tuner
I had three different loads with the same powder charge today and this was the load that had the shortest overall length. The other two longer loads shot about the same group size but the numbers were not as good.
 

Swamppy

Private
Hessian
Minuteman
Apr 18, 2019
75
11
Seating depth changes should have little to no effect on ES and sd of the same charge weight. Neck tension variance can play a considerable role in es and sd's. I would double check you neck tension and start eliminating variables from there.
 

Jmccracken1214

Gunny Sergeant
PX Member
Minuteman
Dec 10, 2018
931
343
Thomasville, NC
Seating depth changes should have little to no effect on ES and sd of the same charge weight. Neck tension variance can play a considerable role in es and sd's. I would double check you neck tension and start eliminating variables from there.
I was wondering if this could be the issue. I am just using the basic hornafy dies. Wondering if I should upgrade to a nicer set for more consistent neck tension.
 

Swamppy

Private
Hessian
Minuteman
Apr 18, 2019
75
11
I was wondering if this could be the issue. I am just using the basic hornafy dies. Wondering if I should upgrade to a nicer set for more consistent neck tension.
I use a mandrel and get the ID of the case neck consistent. That would eliminate the expense of purchasing a new die.
 
  • Like
Reactions: Jmccracken1214

Jmccracken1214

Gunny Sergeant
PX Member
Minuteman
Dec 10, 2018
931
343
Thomasville, NC
I use a mandrel and get the ID of the case neck consistent. That would eliminate the expense of purchasing a new die.
Good call. I already have a mandrel and the die from Sinclair that I use with my 65. What would be the best way to figure out what size mandrel I should get for this 2 23?
 

Swamppy

Private
Hessian
Minuteman
Apr 18, 2019
75
11
Good call. I already have a mandrel and the die from Sinclair that I use with my 65. What would be the best way to figure out what size mandrel I should get for this 2 23?
Pretty sure they only have 2 Sinclair mandrel sizes: expander which is .001 under bullet diameter and turning mandrel .002 under bullet diameter. do not quote me on this they may have added more to there line.
 

CoryT

Gunny Sergeant
PX Member
Minuteman
  • Mar 5, 2004
    1,490
    404
    63
    Paulden, AZ
    www.gunsite.com
    ES and SD have little relation to precision, at least until the range extends enough that vertical spread becomes an issue. ES is basically meaningless, it's possible to use it to reject a long range load, but otherwise it has no value. SD is meaningful to estimate maximum vertical dispersion at long ranges, but only if it's measured over a 20+ shot string. An ES of 4 and an SD of 1.4 is pretty much impossible to measure without Doppler (and no, the LabRadar does not qualify) as the inherent instrument error is greater that that.

    If you have an SD of 10fps over a 20 shot string with a quality chronograph properly setup, that's probably as good as you can get. In that case, you could conceivably have an ES of 60 ( +/- 3 SD). In a 40 shot string you could also easily have 3 shots with exactly the same instrument velocity, giving you an ES of 0 and SD of 0.

    Most people did not do well in their statistics and probability class.

    Precision and accuracy are not the same thing. The displayed problem is one of precision. Many possible reasons for this, none of which are related to the velocity spread/deviation.

    Does the rifle shoot any factory match ammo well? If so, it may be best to start trying to replicate that, so one can eliminate problems in the reloading process
     
    • Like
    Reactions: smoothy8500

    Milo 2.5

    The Dalai Lama of the Reload
    PX Member
    Minuteman
    Aug 7, 2014
    2,547
    1,680
    Gillette, WY
    I have only had one Tikka, a 10tw 243, but have read, most tikka's have some screwed up freebore lengths. I would try find bullet to land relationship if you have not. What bullet and powder are you using, there are some easy combo's out there that may simplify things.
     

    Jmccracken1214

    Gunny Sergeant
    PX Member
    Minuteman
    Dec 10, 2018
    931
    343
    Thomasville, NC
    I have only had one Tikka, a 10tw 243, but have read, most tikka's have some screwed up freebore lengths. I would try find bullet to land relationship if you have not. What bullet and powder are you using, there are some easy combo's out there that may simplify things.
    8208 and 77 smk.

    I seated some at AR mag length just to see how they do jumping.

    I have tried at the lands, .02 off, .025, .030 off....

    Seems the deeper I seat them, the more promise my SD shows. Have had some really good groups but numbers not so much.

    Will report back tomorrow after I shoot the mag length ones
     
    • Like
    Reactions: Milo 2.5

    Dthomas3523

    Hall Monitor
    Staff member
    Moderator
    Hessian
    Commercial Supporter
    PX Member
    Minuteman
    Online Training Access
  • Jan 31, 2018
    9,859
    12,995
    South Texas
    Haven’t read through all the replies, but here’s the skinny on group size and velocity (sd and es).

    At 100 yds, velocity doesn’t matter. There’s not going to be much correlation with group size and velocity

    Distance/time is what matters with velocity. You can play with your calculator/software and see what kind of MV variations will be too much to shoot the size group you want at a particular distance.

    The further you are, it takes less ES to make a large group.

    Then you can get into things like positive compensation at a certain distance which helps overcome the velocity difference by utilizing barrel harmonics.
     
    • Like
    Reactions: Steel head

    Wheres-Waldo

    Gunny Sergeant
    PX Member
    Minuteman
    Nov 2, 2008
    1,539
    340
    Tallahassee, Fl
    Tight groups at 100-500 come from being in a harmonic node.

    Low ES/SD comes from small sample sizes and good loading practice.

    I never have seen a single digit ES/SD snapshot with a real worldly meaningful sample size. What that sample size should be is subjective, but in my mind, if your ES grows from 8FPS to 20FPS just by doubling your sample size, your smaller sample is invalid.

    Truth be told, a 30 FPS ES means 1/2MOA vertical at 1000 in a 6CMoor at 3100FPS. When my limiting factor on performance at 1000 is that my group is a whopping 1/2MOA tall, I’ll start chasing lower numbers.
     
    • Like
    Reactions: Gustav7

    smoothy8500

    Private
    PX Member
    Minuteman
    Online Training Access
    Oct 10, 2012
    539
    276
    South Orange County, CA
    Truth be told, a 30 FPS ES means 1/2MOA vertical at 1000 in a 6CMoor at 3100FPS. When my limiting factor on performance at 1000 is that my group is a whopping 1/2MOA tall, I’ll start chasing lower numbers.
    No kidding, vertical dispersion is the least of my issues shooting F-class T/R. I wish wind calls were as easy as chasing the lands...
     

    Steel head

    Feral kitten
    PX Member
    Minuteman
  • Aug 3, 2014
    11,238
    26,242
    Washington
    Haven’t read through all the replies, but here’s the skinny on group size and velocity (sd and es).

    At 100 yds, velocity doesn’t matter. There’s not going to be much correlation with group size and velocity

    Distance/time is what matters with velocity. You can play with your calculator/software and see what kind of MV variations will be too much to shoot the size group you want at a particular distance.

    The further you are, it takes less ES to make a large group.

    Then you can get into things like positive compensation at a certain distance which helps overcome the velocity difference by utilizing barrel harmonics.
    My favorite AR load has terrible ES but it’s a 600 yard load and does excellent within it intended range.
    I started using that load a decade ago and I’ll probably revisit it because I develop loads entirely different now.

    OP-research powder nodes then look at what Erik cortina does for seating depth nodes.
    Easy load development!
     
    • Like
    Reactions: spoolnaround

    Dthomas3523

    Hall Monitor
    Staff member
    Moderator
    Hessian
    Commercial Supporter
    PX Member
    Minuteman
    Online Training Access
  • Jan 31, 2018
    9,859
    12,995
    South Texas
    My favorite AR load has terrible ES but it’s a 600 yard load and does excellent within it intended range.
    I started using that load a decade ago and I’ll probably revisit it because I develop loads entirely different now.

    OP-research powder nodes then look at what Erik cortina does for seating depth nodes.
    Easy load development!
    So, is the target size large enough the ES doesn’t matter (therefore making the ES perfectly fine vs target size), or are you basically seeing good positive compensation at 600?
     

    Steel head

    Feral kitten
    PX Member
    Minuteman
  • Aug 3, 2014
    11,238
    26,242
    Washington
    So, is the target size large enough the ES doesn’t matter (therefore making the ES perfectly fine vs target size), or are you basically seeing good positive compensation at 600?
    It will hold about 1.5 moa.
    that’s plenty good for a general purpose at load and thrown with a powder measure.
    My 77 smk load is for more precise needs and has a better ES.
     
    • Like
    Reactions: Dthomas3523

    smoothy8500

    Private
    PX Member
    Minuteman
    Online Training Access
    Oct 10, 2012
    539
    276
    South Orange County, CA
    Then you can get into things like positive compensation at a certain distance which helps overcome the velocity difference by utilizing barrel harmonics.
    are you basically seeing good positive compensation at 600?
    Can you explain positive compensation to me? I'm trying to understand what you are describing.
     

    Dthomas3523

    Hall Monitor
    Staff member
    Moderator
    Hessian
    Commercial Supporter
    PX Member
    Minuteman
    Online Training Access
  • Jan 31, 2018
    9,859
    12,995
    South Texas
    Can you explain positive compensation to me? I'm trying to understand what you are describing.
    Google will provide better than I can type. But here’s the cliff notes:

    You are tuning to your barrel “harmonics” (harmonics probably isn’t the absolute perfect word, but that’s what most people understand) for a given distance.

    You are tuning so that slower rounds exit the barrel at a time when during the barrel “whip” the muzzle is pointed higher. This in turn makes up for the velocity difference. It’s basically only good for the range in which you adjust/tune for with seating depth and/or a tuner.

    For example:

    You have a rifle tuned at 1k yds. You fire 5 shots with a labradar showing all the velocities. They are:

    2950
    2960
    2955
    2970
    2940

    Your low is 2940 and high is 2970. @1k that’s a .1 or so difference. That’s 3.6”. But you’re still able to hit X’s (just using F class as an example for the target size) which is 5”. Well, if you have 3.6” of vertical just in the MV variance, what’s happening here?

    You have the rifle tuned where the faster rounds are exiting the barrel on when it’s “pointed down” and the slower exiting when it’s “pointed up” during the barrel whip, so they are grouping better than the math says they should be able to do.

    This is why you’ll see a lot of “people put too much effort into ES. I’ve had ammo with a wide spread in velocity still shoot a small group at X yds.” And when you see their MV variation, the math says it’s impossible to shoot a group that size.

    That’s the theory anyway. And anytime someone says they don’t believe it (I’m completely open to it not being real), I always ask “well, what is the explanation when someone consistently shoots groups that should be mathematically impossible based on the MV variation, and they are a skilled enough shooter it’s not just luck?”

    So far, no one has been able to provide an explanation as to how it happens when the math says it shouldn’t.......without positive compensation being the answer.
     

    Dthomas3523

    Hall Monitor
    Staff member
    Moderator
    Hessian
    Commercial Supporter
    PX Member
    Minuteman
    Online Training Access
  • Jan 31, 2018
    9,859
    12,995
    South Texas
    Now, can most people hold a standard bipod and rear squeeze bag stable enough to tune a 30fps ES like the example? Likely not. You’ll need a front rest and ear bag to benefit.

    But, when you see .5 moa groups at distance with either factory ammo, or handloads with 60fps ES, then something is still happening.
     

    smoothy8500

    Private
    PX Member
    Minuteman
    Online Training Access
    Oct 10, 2012
    539
    276
    South Orange County, CA
    So far, no one has been able to provide an explanation as to how it happens when the math says it shouldn’t
    Ok, kind of like Newberry's OCW? It explains why a test load I tried at 1k that has an SD of 35 still had a fairly flat elevation dispersion. The three high impacts were sighters.
     
    Last edited:

    Dthomas3523

    Hall Monitor
    Staff member
    Moderator
    Hessian
    Commercial Supporter
    PX Member
    Minuteman
    Online Training Access
  • Jan 31, 2018
    9,859
    12,995
    South Texas
    Ok, kind of like Newberry's OCW. It explains why a test load I tried at 1k that has an SD of 35 still had a fairly flat elevation dispersion. The three high impacts were sighters.
    Yes Sir. Same idea. If you do the math, you’ll likely find your vertical dispersion should have been larger (not sure how accurate the velocity is with the shot marker, but I’m sure it’s close enough).
     
    • Like
    Reactions: smoothy8500