Erik Cortina
Team Lapua Brux Borden Captain
I found this target, and I think it's a perfect example of how some people might choose the wrong load because they fell in love with a group without reading the groups properly. This target was shot with my 6.5x47 Lapua and 139 gr. Lapua Scenars with VV N550 powder.
At plain sight, 38.5 gr. appears to be the best group, but if you look at the groups next to it they don't hit the target on the same place vertically in relation to the bull's eye. The load is not stable and this load would cause problems when moving further out because it is not inside the accuracy node.
However, loads 39.5, 40.0, and 40.5 are vertically in the same place in relation to the bull's eye. This is the accuracy node for powder charge, my next step would be to load 40.0 gr. and adjust seating depth and bring the group in and done, I now have a load that would shoot out to 1,000 yards. Also, when the groups line up vertically, the speed also varies very little over the chronograph for the loads that line up on target, it appears that the speed flat lines for a while before it starts to jump up again, this is where you want to be.
Update: 9/17/14
Some of you have asked for more detailed instructions on how I do this. Here they are:
1. Find Jam by seating a bullet long on a dummy piece of brass (no primer nor powder) and apply die wax to the bullet ogive and record it's base to ogive length.
2. Chamber the round and close the bolt.
3. Snap the bolt open and measure the base to ogive measurement. If it is shorter than previous measurement, this is your jam. Do it a few times with different cases to make sure.
4. Load a known powder/primer/bullet combination. I load 4 of each powder charge in 0.5 gr. increments and seat bullets at jam - .020". I use one shot of each to get barrel fouled up and also keep an eye for max pressure at the same time. You can also use these rounds to break in a barrel if you are inclined to. If I encounter pressure on the hotter rounds, I will not shoot groups with the other loaded rounds and will pull bullets when I get back home. Do not shoot in round robin style because position and natural point of aim will be compromised.
5. Shoot 3 shot groups starting from lowest to highest. All groups are shot over a chronograph.
6. Examine target and find the place where consecutive groups line up vertically and ES is the lowest and speed increases the least from one group to the next.
7. Load to the middle of the powder node and do a seating depth test.
8. Load 3 shot groups starting from Jam - 0.005" all the way out to Jam - .040" in .003" increments.
9. When you find the seating depth test that shoots the best, load towards the longest side of the node to allow more room for throat erosion.
10. Final step is to load the new seating depth and load 5 shot groups in 0.1 gr. increments 0.5 gr. on each side of node (if pressure limits are not reached). This will cover an entire grain of powder and you will be able to pinpoint where the powder node starts and ends. In the summer, load towards the low end of the node, and do the opposite in the winter.
HAPPY SHOOTING!
Update 3/29/15
A step I have added lately to my process is to do the powder charge test with multiple primers to see which one shows best potential as well as more consistent chronograph numbers. The primers that performs best during the powder charge testing is the one that I will do the seating depth testing with.
If you find this method helpful in any way, think about making a donation to this great site.
Thank you.
At plain sight, 38.5 gr. appears to be the best group, but if you look at the groups next to it they don't hit the target on the same place vertically in relation to the bull's eye. The load is not stable and this load would cause problems when moving further out because it is not inside the accuracy node.
However, loads 39.5, 40.0, and 40.5 are vertically in the same place in relation to the bull's eye. This is the accuracy node for powder charge, my next step would be to load 40.0 gr. and adjust seating depth and bring the group in and done, I now have a load that would shoot out to 1,000 yards. Also, when the groups line up vertically, the speed also varies very little over the chronograph for the loads that line up on target, it appears that the speed flat lines for a while before it starts to jump up again, this is where you want to be.
Update: 9/17/14
Some of you have asked for more detailed instructions on how I do this. Here they are:
1. Find Jam by seating a bullet long on a dummy piece of brass (no primer nor powder) and apply die wax to the bullet ogive and record it's base to ogive length.
2. Chamber the round and close the bolt.
3. Snap the bolt open and measure the base to ogive measurement. If it is shorter than previous measurement, this is your jam. Do it a few times with different cases to make sure.
4. Load a known powder/primer/bullet combination. I load 4 of each powder charge in 0.5 gr. increments and seat bullets at jam - .020". I use one shot of each to get barrel fouled up and also keep an eye for max pressure at the same time. You can also use these rounds to break in a barrel if you are inclined to. If I encounter pressure on the hotter rounds, I will not shoot groups with the other loaded rounds and will pull bullets when I get back home. Do not shoot in round robin style because position and natural point of aim will be compromised.
5. Shoot 3 shot groups starting from lowest to highest. All groups are shot over a chronograph.
6. Examine target and find the place where consecutive groups line up vertically and ES is the lowest and speed increases the least from one group to the next.
7. Load to the middle of the powder node and do a seating depth test.
8. Load 3 shot groups starting from Jam - 0.005" all the way out to Jam - .040" in .003" increments.
9. When you find the seating depth test that shoots the best, load towards the longest side of the node to allow more room for throat erosion.
10. Final step is to load the new seating depth and load 5 shot groups in 0.1 gr. increments 0.5 gr. on each side of node (if pressure limits are not reached). This will cover an entire grain of powder and you will be able to pinpoint where the powder node starts and ends. In the summer, load towards the low end of the node, and do the opposite in the winter.
HAPPY SHOOTING!
Update 3/29/15
A step I have added lately to my process is to do the powder charge test with multiple primers to see which one shows best potential as well as more consistent chronograph numbers. The primers that performs best during the powder charge testing is the one that I will do the seating depth testing with.
If you find this method helpful in any way, think about making a donation to this great site.
Thank you.
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