Kyle Schultz
Gold $$ Contributor
I'm new to SR group shooting. I recently had my 6 PPC barrel (146 rds) threaded for Mike Ezell's PDT tuner. I previously had tuned the bare barrel at 29.2 gr N133 using Bart's Bullets 68gr Avenger bullet seated 0.012" into the lands from a touch.
Yesterday I installed the tuner. It "bottomed out" at a setting of 18. I then backed it out 1/2 turn until the "0" mark on the tuner lined up with the witness mark on the barrel. I then shot 3-shot groups at each setting. If the 2-shot group was not good, I did not shot the 3rd shot. The 2-shot groups are marked with an asterisk. Target below.
Some interesting results. The "book" says that the nodes repeat themselves about every 8 tuner marks. And I pretty much saw that behavior. I had good nodes at 0/1, again at 8/9/10, and again at 19/20/21. I mistakenly shot setting 27 twice and while the first group was good, the second was not so who knows.
At the end of the day, I reshot groups at tuner settings 19, 10 and 1. Target not attached. The groups for 19 and 10 were not good but the 5-shot group at 1 was good. I roughly measured the group size at 0.157".
It does appear to me that the groups print systematically. POA was 12 o'clock on the moth ball. You clearly can see the POI of the groups fall from 0 to 8 and then start climbing. From a peak at 14 the groups trend lower until they bottom out around setting 21. Then they start climbing again.
One mistake I may have made was shooting this test with once-fired brass. The final 5-shot group at 1 that shot the 0.157 group was shot with twice-fired brass. Their average velocity was 23 fps faster than the average for the once-fired brass.
My plans are now to retest 2 regions (dare I say... quadrants) of the tuner. That being the settings around 0/1 and the settings around 19/20/21.
Your comments and advice are welcomed and appreciated.
Yesterday I installed the tuner. It "bottomed out" at a setting of 18. I then backed it out 1/2 turn until the "0" mark on the tuner lined up with the witness mark on the barrel. I then shot 3-shot groups at each setting. If the 2-shot group was not good, I did not shot the 3rd shot. The 2-shot groups are marked with an asterisk. Target below.
Some interesting results. The "book" says that the nodes repeat themselves about every 8 tuner marks. And I pretty much saw that behavior. I had good nodes at 0/1, again at 8/9/10, and again at 19/20/21. I mistakenly shot setting 27 twice and while the first group was good, the second was not so who knows.
At the end of the day, I reshot groups at tuner settings 19, 10 and 1. Target not attached. The groups for 19 and 10 were not good but the 5-shot group at 1 was good. I roughly measured the group size at 0.157".
It does appear to me that the groups print systematically. POA was 12 o'clock on the moth ball. You clearly can see the POI of the groups fall from 0 to 8 and then start climbing. From a peak at 14 the groups trend lower until they bottom out around setting 21. Then they start climbing again.
One mistake I may have made was shooting this test with once-fired brass. The final 5-shot group at 1 that shot the 0.157 group was shot with twice-fired brass. Their average velocity was 23 fps faster than the average for the once-fired brass.
My plans are now to retest 2 regions (dare I say... quadrants) of the tuner. That being the settings around 0/1 and the settings around 19/20/21.
Your comments and advice are welcomed and appreciated.
