Hello, I am trying to develop a load for my Rifle, 308 desert tech Covert and I appear to be getting inconsistent chronograph readings. I am also a bit dubious about relying upon my group sizes as my position (Bench rest) was becoming inconsistent/unsteady.
I was shooting in a Pipe Range and the chronograph measurements and group sizes were provided by the installed Shotmarker system. The Shotmaster system appears to be indicating some 200fps and more, higher than expected velocities based upon comparing both measured velocities using my chronograph and derived velocities using Dope with OME rounds.
The measurements were taken over a number of days, however I loaded up four rounds for each load and shot only three rounds of each, unless I had a flyer, the fourth rounds I shot at the following visit to act as a control so I compared the velocity of the first and second visits to see if they were consistent - they were. The first and second visited appeared to indicate a Node at 42.9gn. Loads between 42 and 43.8 gns were fired over the first two days.
The real confusion occurs after the third days shooting, with rounds loaded between 43.9 & 45gns.
Just for the record I am confident that the reloading process was consistent, new Lapua Brass was used, Bullets are 175gn SMK, Vhit Powder N140.
Please find a graph below of the Velocity measurements I have also included a pdf file of the actual readings from the spreadsheet. The readings from the first days shooting only consist of Group measurements. the remaining two days I manually recorded each round velocity. The only apparent difference is that on day three (a large fan had been placed in the Range which increased the air flow in the room and cooled the room down on the day, was a warm day 23deg to start with this dropped to 17 deg, the temperature in the room on earlier visits was in the 16, 17degC region.
Appreciate any assistance, Regards, Phil
I was shooting in a Pipe Range and the chronograph measurements and group sizes were provided by the installed Shotmarker system. The Shotmaster system appears to be indicating some 200fps and more, higher than expected velocities based upon comparing both measured velocities using my chronograph and derived velocities using Dope with OME rounds.
The measurements were taken over a number of days, however I loaded up four rounds for each load and shot only three rounds of each, unless I had a flyer, the fourth rounds I shot at the following visit to act as a control so I compared the velocity of the first and second visits to see if they were consistent - they were. The first and second visited appeared to indicate a Node at 42.9gn. Loads between 42 and 43.8 gns were fired over the first two days.
The real confusion occurs after the third days shooting, with rounds loaded between 43.9 & 45gns.
Just for the record I am confident that the reloading process was consistent, new Lapua Brass was used, Bullets are 175gn SMK, Vhit Powder N140.
Please find a graph below of the Velocity measurements I have also included a pdf file of the actual readings from the spreadsheet. The readings from the first days shooting only consist of Group measurements. the remaining two days I manually recorded each round velocity. The only apparent difference is that on day three (a large fan had been placed in the Range which increased the air flow in the room and cooled the room down on the day, was a warm day 23deg to start with this dropped to 17 deg, the temperature in the room on earlier visits was in the 16, 17degC region.
Appreciate any assistance, Regards, Phil
