@josebd,
I’ve followed Erik’s test protocol to a tee. Take a look at steps 5-10. The Cortina method is not to identify one specific group that is the tightest, but the entire node (consisting of multiple groups) that show the least vertical variance from the bottom powder charge to the top. In your set of pictures 43.5 looks like the tighest single group, but where does the center of that group line up with the 43.0 powder charge as well as the 44.0 powder charge? 43.5 centers 1/2” below your POI, while 44.0, 44.5, and 45.0 seem to center closer to your POI. I might therefore use 44.5 as the start of step number 7 below.
Did you chrono your shots to compare speed to your target results? This can provide confirmation that you’ve found a good node.
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.
I’ve followed Erik’s test protocol to a tee. Take a look at steps 5-10. The Cortina method is not to identify one specific group that is the tightest, but the entire node (consisting of multiple groups) that show the least vertical variance from the bottom powder charge to the top. In your set of pictures 43.5 looks like the tighest single group, but where does the center of that group line up with the 43.0 powder charge as well as the 44.0 powder charge? 43.5 centers 1/2” below your POI, while 44.0, 44.5, and 45.0 seem to center closer to your POI. I might therefore use 44.5 as the start of step number 7 below.
Did you chrono your shots to compare speed to your target results? This can provide confirmation that you’ve found a good node.
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.
