I am only neck sizing and trimm after firing. The powder is Reloder 16, Lapua 6.5 Creedmoor Brass, FGMM Small Rifle Primers, 140gr Berger Hybrid Bullets.
The first 2 firings were 10 shots from 38.6 to 42.2 @ .4 gr increments.
The third firing was an OCW done with round robin of the powder charges 38.6 to 42.2 @ .2 gr increments (5 shots each).
Based on the data, the muzzle velocity increases with each firing of the brass. It seems to converge at higher powder charges. I first thought this might be due to the barrel heating up but the muzzle velocities of the round robin don't indicate any increase in velocity due to chamber heat. You would think that the avg MV for the 42.2gr charge on an OCW test would be lower than firing 90 rounds first (42.2gr being firings 90-100 instead of 20,40,60,80,100). The temperatures for the two days were similar 80-90 F for the third firing and 76 - 85 F for the second firing. I find it hard to believe that the temperature insensitive RL-16 powder is thrown off that much by less than 10 degrees, not to mention the first firing was lower then both and had temps of 80 - 89 F. My first thought was it took energy to expand the virgin brass to the chamber so that took away from MV, but after the second firing would it still be stretching significantly? Or is this a product of work hardening the brass (I do not have an annealer yet) causing increased neck tension?
Here is the google doc excel sheet with all my data and graphs, let me know if you think I am missing something and I'll see if I noted it down. From what I understand temperature is what effects muzzle velocity but I also have notes of density altitude.
https://docs.google.com/spreadsheets/d/1qmPC4-HVH1wtLMy8uW3QtkAOOy0yZa2jQKpPUqJFYpw/edit#gid=0
POI's for all three firings seem to follow the same pattern, so at least I have that:
http://imgur.com/lzvNErx
The first 2 firings were 10 shots from 38.6 to 42.2 @ .4 gr increments.
The third firing was an OCW done with round robin of the powder charges 38.6 to 42.2 @ .2 gr increments (5 shots each).
Based on the data, the muzzle velocity increases with each firing of the brass. It seems to converge at higher powder charges. I first thought this might be due to the barrel heating up but the muzzle velocities of the round robin don't indicate any increase in velocity due to chamber heat. You would think that the avg MV for the 42.2gr charge on an OCW test would be lower than firing 90 rounds first (42.2gr being firings 90-100 instead of 20,40,60,80,100). The temperatures for the two days were similar 80-90 F for the third firing and 76 - 85 F for the second firing. I find it hard to believe that the temperature insensitive RL-16 powder is thrown off that much by less than 10 degrees, not to mention the first firing was lower then both and had temps of 80 - 89 F. My first thought was it took energy to expand the virgin brass to the chamber so that took away from MV, but after the second firing would it still be stretching significantly? Or is this a product of work hardening the brass (I do not have an annealer yet) causing increased neck tension?
Here is the google doc excel sheet with all my data and graphs, let me know if you think I am missing something and I'll see if I noted it down. From what I understand temperature is what effects muzzle velocity but I also have notes of density altitude.
https://docs.google.com/spreadsheets/d/1qmPC4-HVH1wtLMy8uW3QtkAOOy0yZa2jQKpPUqJFYpw/edit#gid=0
POI's for all three firings seem to follow the same pattern, so at least I have that:
http://imgur.com/lzvNErx
