Low ES, Low SD = poor groups ?

[Fore300]

I have been working up some loads and find often that the loads with the lowest SD and lowest ES are typically producing poor groupings. Is this normal? Am I missing something? I thought a low SD and ES would be giving you your best accuracy.
Does anyone else find this issue or comments

 

[Chilly807]

Barrel harmonics plays a role in group size. If the muzzle is relatively "quiet" as the bullet exits there's a better chance you will have good groups, at least at close range, such as 100 yds.
The problem with that is, at longer ranges if your velocity spread isn't good you will have a pronounced vertical element to your groups.
Ladder testing can help you find both a forgiving powder charge that yields a consistent muzzle velocity and also produces a favourable vibration caused by that velocity.
Do a Google search using Creighton Audette ladder test as keywords. Also optimal charge weight or OCW test. Both are interesting reading.

 

[4n2t0]

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[cr5]

What caliber are you shooting and at what distance?

Try shooting 200 yards or more for your testing. 100 yards can sometimes be deceiving with certain calibers. My 338 Lapua would shoot one inch at 100 yards and 1 inch at 200 yards with the same load. Sometimes they need 200+ to settle in and show you what it can really do.

Good luck.

 

[Ganderite]

I have been working up some loads and find often that the loads with the lowest SD and lowest ES are typically producing poor groupings. Is this normal? Am I missing something? I thought a low SD and ES would be giving you your best accuracy.
Does anyone else find this issue or comments

You want a rifle that groups well. Good.

Now consider what distance you want it to group well at. The part of the equation that you cannot see is the barrel whip at the muzzle. At a specific distance, the whip can cause the group to be more vertical, less vertical or have no effect.

Your good ES and poor group means the barrel is showing a lot of compensation. The muzzle is moving when the bullet exits. This could be negative or positive compensation, which could be very good or very bad.

Shoot the same load at 500 yards (if a longer distance matters to you - it might not). If the 2 minute group at 100 becomes a 1 minute group at 500, you have positive compensation. There is a distance where the compensation gives maximum benefit (you only find it by shooting at all distances) and this load might very well be better than another load with an even lower ES.

So decide what range matters to you. It might be 100 yards. It might be a longer distance. The ES and SD do not matter. What matters is group size. Find the load that actually gets the best groups out of your rifle.

A ladder test is very useful, if dome properly. ES &SD are no substitute and almost meaningless as a predictor of performance.

I used to be the Technical Director of a ammo company making match ammo for competitors and for military and police snipers. Since we could not develop a load for each rifle, we made ammo with the best ES we could (single digit) and hoped for the best.

 

[todbartell]

Consistent brass volume, consistent charge weights, a powder that burns optimum for the application will give tight ES/SD. If it's off node, it will scatter on target. Try increasing/decreasing charge weight to find where accuracy improves

 

[Mystic Precision]

I have been working up some loads and find often that the loads with the lowest SD and lowest ES are typically producing poor groupings. Is this normal? Am I missing something? I thought a low SD and ES would be giving you your best accuracy.
Does anyone else find this issue or comments

Really depends on how far out is your target... For me, min is 200yds, better is 250 to 300yds. When tuning at these distances, small changes in powder charge will show up very clearly on target. And since we are worried about holes in a target not numbers on a screen, go with the load that groups the best at distance.

Accurate loads will have good ES/SD numbers (not necessarily single digits).... loads with tiny ES/SD numbers may shoot like crap.

Velocity spreads is NOT an indicator of accuracy.. about the only thing it is useful for is to create a drop chart.

YMMV.

Jerry

 

[Ganderite]

Really depends on how far out is your target... For me, min is 200yds, better is 250 to 300yds. When tuning at these distances, small changes in powder charge will show up very clearly on target. And since we are worried about holes in a target not numbers on a screen, go with the load that groups the best at distance.

Accurate loads will have good ES/SD numbers (not necessarily single digits).... loads with tiny ES/SD numbers may shoot like crap.

Velocity spreads is NOT an indicator of accuracy.. about the only thing it is useful for is to create a drop chart.

YMMV.

Jerry

^^ Like he said.

 

[eaglesnester]

Also pay attention to neck tension, it would seem that neck length and trim length variations may also play a roll, and dont forget the gun gods.

 

[JEC]

What caliber are you shooting and at what distance?

Try shooting 200 yards or more for your testing. 100 yards can sometimes be deceiving with certain calibers. My 338 Lapua would shoot one inch at 100 yards and 1 inch at 200 yards with the same load. Sometimes they need 200+ to settle in and show you what it can really do.
Good luck.

My understanding :::: A bullet that is “off course” by 1” at 100yds will be close to 2” “off course” at 200yd (could be a little less >low>gravity) (could be up to 0.1 off>cyclonic/geoscopic swirl) ...assuming no wind drift. A bullet that is rotationally stable as it exits the muzzle typically remains stable during its tracectory as velocity bleeds off more quickly than the rate of rotation. If the “smaller groups at distance” is valid, it should happen with every same twisted bullet at the same velocity,etc? All other things being equal, the explanation is more likely related to parallax?

 

[Ganderite]

My understanding :::: A bullet that is “off course” by 1” at 100yds will be close to 2” “off course” at 200yd (could be a little less >low>gravity) (could be up to 0.1 off>cyclonic/geoscopic swirl) ...assuming no wind drift. Vertically - NO Horizontally YES

If the barrel movement was upwards, the slower bullets will be aimed higher. If the slow bullets printed higher at 100, they will fall back into the group somewhere down range. So a 3 minute group at 100 might be a 1 or 2 minute group at a longer range.


A bullet that is rotationally stable as it exits the muzzle typically remains stable during its trajectory as velocity bleeds off more quickly than the rate of rotation. YES

If the “smaller groups at distance” is valid, it should happen with every same twisted bullet at the same velocity, etc? NO. Barrel whip can be affected by acceleration, even though the exit velocity is the same.

All other things being equal, the explanation is more likely related to parallax? YES. Parallax can screw up groups at a given distance.

Test at the distance that matters.

 

[Fore300]

Thanks guys for the feed back. I typically do my testing at 300 m and I do typically stay with the best groupings. Just thought the best groupings should come from the load the produces the most consistent numbers

 

[rral22]

Thanks guys for the feed back. I typically do my testing at 300 m and I do typically stay with the best groupings. Just thought the best groupings should come from the load the produces the most consistent numbers

Numbers are just that, numbers, and may not reflect accuracy. I have heard of (but never actually observed) rifles that shot better in terms of Minute of Angle at longer ranges than shorter ones, but there is no way a group can get smaller in absolute measurements at longer ranges than they are at any shorter range.

 

[Dogleg]

Much of short range (300 and under) grouping is simply a fortunate accident of bullet exit coinciding with an opportune barrel position. If you have that, and a good bullet in a good barrel good things are bound to happen. You might even be able to tweak it from there. Maybe. If you have a good one its hard to do anything wrong.

Say you have the opposite, the Crap load. (Technical term that I just made up). Know what you're not going to do?

You're not going to lab scale, chronograph, ES, SD, neck turn, weight sort, anneal, primer pocket and flash hole uniform or straight seat a crap load into a good load. It might make a good load into a great load, or at the very least is unlikely to hurt anything.

The target gets to decide what's a good load.

 

[Ganderite]

Numbers are just that, numbers, and may not reflect accuracy. I have heard of (but never actually observed) rifles that shot better in terms of Minute of Angle at longer ranges than shorter ones, but there is no way a group can get smaller in absolute measurements at longer ranges than they are at any shorter range.

Yes they can. This used to be a common occurrence when we used the Lee Enfield as a target rifle.

But you need a well set up rifle and good ammo to see it happen.

Your logic is good. A high shot will keep going higher in the group and a low shot will keep going lower.

But not necessarily.

Suppose the high shots at 100 yards were the slowest shots. And the low shots were the fastest.

At 200 the high shots would drop more (because they are slow) and drop into the main group. And the low shots would drop less (because they are fast) and rise up into the group.

So the 200 yard group might not have the high and low flyers.

We used to tune our #4s to do that at 1000 yards. We had military issue ball ammo with a ES in the order of 50 to 75 and needed the compensation to keep our shots in the bull. It worked well.