help me make sense of this?

[Army-medic]

I've reloaded for several years with good success in .308 but I am struggling with the 6.5 creedmoor.

I have the following results taken by a magneto speed chronograph which includes SD and extreme spread. I was under the impression that the lower the SD and ES; the better.

But although today's groups were far from excellent, there were several loads with good SD and ES that did not group very well at all.


I'm sensible enough to understand that I can see that the groups aren't great but I expected better with some pretty good chronological readings. any thoughts? Is it a case of barrel harmonics and the load not being suitable?



Series 1 Shots: 5
Min 2750 Max 2772
Avg 2765 S-D 8.8
ES 22

Series Shot Speed
1 1 2767 ft/s
1 2 2750 ft/s Group Size: 0.47 MOA
1 3 2770 ft/s
1 4 2772 ft/s
1 5 2769 ft/s
---- ---- ---- ----


Series 2 Shots: 5
Min 2757 Max 2775
Avg 2768 S-D 7.4
ES 18

Series Shot Speed
2 1 2775 ft/s
2 2 2773 ft/s
2 3 2766 ft/s Group size 0.44 MOA
2 4 2757 ft/s
2 5 2773 ft/s
---- ---- ---- ----


Series 3 Shots: 4
Min 2727 Max 2761
Avg 2742 S-D 15.4
ES 34

Series Shot Speed
3 1 2761 ft/s
3 2 2727 ft/s
3 3 2749 ft/s group size : 0.7 MOA
3 4 2733 ft/s
---- ---- ---- ----


Series 4 Shots: 5
Min 2731 Max 2745
Avg 2737 S-D 6.1
ES 14

Series Shot Speed
4 1 2745 ft/s
4 2 2735 ft/s
4 3 2731 ft/s Group size: 1.1 MOA
4 4 2732 ft/s
4 5 2742 ft/s
---- ---- ---- ----


Series 5 Shots: 4
Min 2720 Max 2740
Avg 2731 S-D 8.6
ES 20

Series Shot Speed
5 1 2729 ft/s
5 2 2720 ft/s
5 3 2735 ft/s group size 1 MOA
5 4 2740 ft/s
---- ---- ---- ----


Series 6 Shots: 5
Min 2729 Max 2752
Avg 2736 S-D 9.1
ES 23

Series Shot Speed
6 1 2752 ft/s
6 2 2733 ft/s
6 3 2729 ft/s Group size : 1.2 MOA
6 4 2731 ft/s
6 5 2736 ft/s
---- ---- ---- ----


Series 7 Shots: 4
Min 2705 Max 2728
Avg 2717 S-D 9.4
ES 23

Series Shot Speed
7 1 2719 ft/s
7 2 2705 ft/s Group size: 1.23 MOA
7 3 2716 ft/s
7 4 2728 ft/s
---- ---- ---- ----


Series 8 Shots: 5
Min 2700 Max 2724
Avg 2713 S-D 10
ES 24

Series Shot Speed
8 1 2724 ft/s
8 2 2700 ft/s
8 3 2721 ft/s Group size 0.55 MOA
8 4 2706 ft/s
8 5 2715 ft/s
---- ---- ---- ----


Series 9 Shots: 5
Min 2712 Max 2734
Avg 2722 S-D 9.6
ES 22

Series Shot Speed
9 1 2731 ft/s
9 2 2712 ft/s
9 3 2718 ft/s group size: 1.13 MOA
9 4 2716 ft/s
9 5 2734 ft/s
---- ---- ---- ----


Series 10 Shots: 5
Min 2705 Max 2732
Avg 2717 S-D 11
ES 27

Series Shot Speed
10 1 2732 ft/s
10 2 2705 ft/s
10 3 2707 ft/s Group size: 0.88 MOA
10 4 2720 ft/s
10 5 2721 ft/s

[simgre]

Was it the same bullet used throughout? And by how much did each load vary by?

[Army-medic]

Was it the same bullet used throughout? And by how much did each load vary by?

Same bullet. Two different charges (42.1 and 41.6) 25 rounds of each but 5 different seating depths.

[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?

[tacfoley]

Same bullet. Two different charges (42.1 and 41.6) 25 rounds of each but 5 different seating depths.

At the risk of peeing you off, how did you arrive at the seating depth for, as an example, Group #2, which seems pretty good to me? Can you try any other brand of bullets, say, JLK? They seem to be extremely popular over the way with the 1400 yard gong-ringers and quite moderate loads. Would you like me to ask around?

tac

[Army-medic]

At the risk of peeing you off, how did you arrive at the seating depth for, as an example, Group #2, which seems pretty good to me? Can you try any other brand of bullets, say, JLK? They seem to be extremely popular over the way with the 1400 yard gong-ringers and quite moderate loads. Would you like me to ask around?

tac

The seating depth was decided as simply 10 thou from the lands of a load that up until this point seemed the best option.

I’m open to the idea of trying other bullets but I also note that these lapua 139 bullets seem very accurate in a variety of rifles.

Perhaps I need to explore a grain or two higher than what I currently use or try another powder- I recently bought some RS 62 too.

Thanks for enlightening me on JLK bullets; I’ve not come across them before.

[tacfoley]

The seating depth was decided as simply 10 thou from the lands of a load that up until this point seemed the best option. Thanks for enlightening me on JLK bullets; I’ve not come across them before.

As used in the latest 1000 yard benchrest group of a little over 1" for five shots - shot from a rifle that looks like a rifle and not a piece of laboratory equipment. Used to be made right there at the competition site by Swampy Knox in his truck - J4 jackets and all, sold still hot. He WAS JLK - but sold out to another husband and wife team of national-level BR-ers.

Here in UK it's Fox Firearms who has them -

http://www.foxfirearmsuk.com/index.p...tom-bullets-us

Good luck.

tac