Velocity & OAL
Posted: Thu Sep 01, 2011 8:19 pm
Like many I have read lots re the dangers of changing the OAL of a round and the consequent dangerous rise in pressures.
As I was unhappy with the grouping of the 185gn Berger's I decided that I would act upon the general consensus that they appear to like a jump of 20 or 30 thou.
My starting/previous OAL was 2.150" Deciding to take the process steady, I loaded 47.3 gn of Viht 550 & CCI BR primers at .005 stages starting at 2.130" and fired 10 each over the chrono from the bench. My barrel is 32" long and is of course .308 cal.
Ovenpaa can note that despite his best efforts, the chrono is still working and that rain water on the sensors must have been the reason for the previous outings error messages, not his attempt at murdering his chrono.
2.130 = ave 2775fps
2.125 = ave 2779fps
2.120 = ave 2783fps
2.115 = ave 2799fps?
2.110 = ave 2785fps
2785fps is a good velocity for the distances I shoot, so I will stay with that one for the time being.
So not the great leaps in velocity that I was expecting between loads. All cases were checked for pressure and all appeared OK. This does surprise me and I may start to ease up a bit on making sure each case is exactly the OAL that I am aiming for.
Having said that I am still struggling to get small average spreads. The lowest was 22fps for the 2.110 and that was marginally the smallest group.
The highest was 55fps and this is despite taking a painfully long time over each load, dropping the last few kernels in by trickler.
I am starting to wonder about my case preparation and am wondering if I am going to have to invest time and money in making sure all the neck variables are taken care of. I seriously do not want to have to spend more time on my brass and would have liked to have written these procedures off to mind games.
At 114 yards all the groups were in the 1" range. Not at all impressive, but before I continue to kick my self I will remember that those Short Siberia tables/chairs are useless as far as I am concerned in achieving accuracy. With a different position/grip with each shot. I really need to get prone to get the best out of the kit.
I was also aiming at patches placed around the target, as these are not the smallest aiming mark, they also will have contributed to larger groups.
Excuses excuses etc,
DM
As I was unhappy with the grouping of the 185gn Berger's I decided that I would act upon the general consensus that they appear to like a jump of 20 or 30 thou.
My starting/previous OAL was 2.150" Deciding to take the process steady, I loaded 47.3 gn of Viht 550 & CCI BR primers at .005 stages starting at 2.130" and fired 10 each over the chrono from the bench. My barrel is 32" long and is of course .308 cal.
Ovenpaa can note that despite his best efforts, the chrono is still working and that rain water on the sensors must have been the reason for the previous outings error messages, not his attempt at murdering his chrono.
2.130 = ave 2775fps
2.125 = ave 2779fps
2.120 = ave 2783fps
2.115 = ave 2799fps?
2.110 = ave 2785fps
2785fps is a good velocity for the distances I shoot, so I will stay with that one for the time being.
So not the great leaps in velocity that I was expecting between loads. All cases were checked for pressure and all appeared OK. This does surprise me and I may start to ease up a bit on making sure each case is exactly the OAL that I am aiming for.
Having said that I am still struggling to get small average spreads. The lowest was 22fps for the 2.110 and that was marginally the smallest group.
The highest was 55fps and this is despite taking a painfully long time over each load, dropping the last few kernels in by trickler.
I am starting to wonder about my case preparation and am wondering if I am going to have to invest time and money in making sure all the neck variables are taken care of. I seriously do not want to have to spend more time on my brass and would have liked to have written these procedures off to mind games.
At 114 yards all the groups were in the 1" range. Not at all impressive, but before I continue to kick my self I will remember that those Short Siberia tables/chairs are useless as far as I am concerned in achieving accuracy. With a different position/grip with each shot. I really need to get prone to get the best out of the kit.
I was also aiming at patches placed around the target, as these are not the smallest aiming mark, they also will have contributed to larger groups.
Excuses excuses etc,
DM