Hello all,
So today I came across an issue that has been nagging at my soul since I've come back from the range. I have been recently working up some loads for a buddy's 700 AAC and concluded upon 40.5 grains of RE15 inside of a once fired LC '05 case and a 175 grain SMK on top (COAL 2.805). We chronoed a string of 10 shots that averaged 2623 FPS and it shot very, very well.
One week later...
Today, we replicated the same exact load and used the exact same components and specifications that performed well already. Now, the cases are being fired for the third time. Just for curiosity, I set up the chronograph and check the velocity for the next string of 10 rounds. To my Surprise, these loads now averaged a velocity of 2273. We shot at the exact location as before with weather being quite similar each outing.
After thinking about this quite hard since earlier today, my conclusion is that case erosion may have played a significant role in this deteriorated velocity; however, in all my years as a reloader, I have never seen such a significant change in velocity between the second and third reload. What puzzles me even more is that my M1A was capable of producing an even higher velocity with a lower charge than the 700 AAC (This was done using LC '10 brass on its second reload).
Although I did not weigh the LC '05 brass before I fired them out of my buddies gun, I did weigh them afterwards and they averaged 175 grains (This weight is after 3 reloads). I did not have any more LC '05 brass but I did weigh some LC '10 that weighed 179 grains (twice fired). I know that the weight of brass is not Completely indicative of internal case volume but if I must say, I have put many reloads downrange without ever having to worry about the case volume of every case.
Note: I was also using CCI 34 primers.
So today I came across an issue that has been nagging at my soul since I've come back from the range. I have been recently working up some loads for a buddy's 700 AAC and concluded upon 40.5 grains of RE15 inside of a once fired LC '05 case and a 175 grain SMK on top (COAL 2.805). We chronoed a string of 10 shots that averaged 2623 FPS and it shot very, very well.
One week later...
Today, we replicated the same exact load and used the exact same components and specifications that performed well already. Now, the cases are being fired for the third time. Just for curiosity, I set up the chronograph and check the velocity for the next string of 10 rounds. To my Surprise, these loads now averaged a velocity of 2273. We shot at the exact location as before with weather being quite similar each outing.
After thinking about this quite hard since earlier today, my conclusion is that case erosion may have played a significant role in this deteriorated velocity; however, in all my years as a reloader, I have never seen such a significant change in velocity between the second and third reload. What puzzles me even more is that my M1A was capable of producing an even higher velocity with a lower charge than the 700 AAC (This was done using LC '10 brass on its second reload).
Although I did not weigh the LC '05 brass before I fired them out of my buddies gun, I did weigh them afterwards and they averaged 175 grains (This weight is after 3 reloads). I did not have any more LC '05 brass but I did weigh some LC '10 that weighed 179 grains (twice fired). I know that the weight of brass is not Completely indicative of internal case volume but if I must say, I have put many reloads downrange without ever having to worry about the case volume of every case.
Note: I was also using CCI 34 primers.
