help me make sense of this?

[Randy Bohannon]

The ES and SD figures give a measure of the internal ballistic consistency of the load.






Tight grouping at close range has more to do with the point in the harmonic vibration of the barrel the bullet leaves the bore.

At long range small difference in velocity can make large difference in elevation at the target, with corresponding sensitivity to wind.

At long range you need both a small group and small variance between shots in that group whereas in at short range it doesn't make much difference.

In other words and with the lapua 139 gr scenar as an example:

1000 yard drop @ 2700 fps = -347.7" windage: 82.7"

1000 yard drop @ 2750 fps = 332.9" windage: 80.2"

So at 1000 yards 50 fps extreme spread will result in 15" of vertical and 2.5" of horizontal random dispersion.

At 200 yards

200 yard drop @ 2700 fps = -3.9 drop windage 2.5"

200 yard drop @ 2750 fps = -3.7 drop windage 2.4"

At 200 yards the difference is 0.2" vertical and 0.1" horizontal.

So a load that leaves the barrel at a node in the firing cycle may be very accurate at short range.

Similarly a load which doesn't may have very consistent internal ballistics.

[Army-medic]

The ES and SD figures give a measure of the internal ballistic consistency of the load.






Tight grouping at close range has more to do with the point in the harmonic vibration of the barrel the bullet leaves the bore.

At long range small difference in velocity can make large difference in elevation at the target, with corresponding sensitivity to wind.

At long range you need both a small group and small variance between shots in that group whereas in at short range it doesn't make much difference.

In other words and with the lapua 139 gr scenar as an example:

1000 yard drop @ 2700 fps = -347.7" windage: 82.7"

1000 yard drop @ 2750 fps = 332.9" windage: 80.2"

So at 1000 yards 50 fps extreme spread will result in 15" of vertical and 2.5" of horizontal random dispersion.

At 200 yards

200 yard drop @ 2700 fps = -3.9 drop windage 2.5"

200 yard drop @ 2750 fps = -3.7 drop windage 2.4"

At 200 yards the difference is 0.2" vertical and 0.1" horizontal.

So a load that leaves the barrel at a node in the firing cycle may be very accurate at short range.

Similarly a load which doesn't may have very consistent internal ballistics.

So what can I infer from my own data? That my reloading practice is relatively consistent as exemplified by a relatively low SD and ES but that the harmonics may be off for this particualr load to be suited to my rifle?

[Randy Bohannon]

I think you can infer that your loading process does indeed produce consistent ammo, that rifle prefers the higher charge weight, prefers the shorter OAL ( if I have guessed your series progression right) and that loads 1 and 2 are worth experimenting further with.

I wouldn’t place too much faith in exact ES and SD figures as your sample sizes are too small but they do illustrate “high” or “low” reasonably well.

If I recall you are in search of a higher velocity node, I would like to see your work up results but it seems from what you have given the node could be about a grain higher than your 42.1 load.

are you seeing pressure signs?

What weight of bullet are you using?

[Army-medic]

I think you can infer that your loading process does indeed produce consistent ammo, that rifle prefers the higher charge weight, prefers the shorter OAL ( if I have guessed your series progression right) and that loads 1 and 2 are worth experimenting further with.

I wouldn’t place too much faith in exact ES and SD figures as your sample sizes are too small but they do illustrate “high” or “low” reasonably well.

If I recall you are in search of a higher velocity node, I would like to see your work up results but it seems from what you have given the node could be about a grain higher than your 42.1 load.

are you seeing pressure signs?

What weight of bullet are you using?

No pressure signs at 42.1 which is the max load according to Vihtavouri.

Using Lapua 139 scenar 6.5mm bullet

[Black Beard]

Were they the same load as the velocity was dropping? Could be the barrel warming up.

[Parabuteo]

Have you considered a ladder test?

[sarge4318]

Have you considered binning the chronograph?

Don't sweat the figures, just shoot (ladder test groups like Chris suggests) and tweek loads from there to get a group you're happy with, then shoot over the chronograph and see what it says.