Because I guess I have too much time on my hands or because I am a freak, I decided to sort my 17HMR ammo by concentricity to see if it would make a difference. 22LR ammo won't fit in my Sinclair's concentricity guage, but on 17HMR, with the two blocks as close together as possible and with some diligence, I can take some runout readings.
My distribution looked like this:
Runout % of Population
0-1....... 2%
1-2....... 10%
2-3....... 19%
3-4....... 19%
4-5....... 18%
5&+....... 33%
These runout numbers are in thousandths of an inch. I could mention brand, but it is all made by CCI, so it doesn't matter. The bullet is V-Max.
Here are the targets
5 and up runout:
1-2 runout:
My >5 target doesn't look so bad because the POI is very centered. On the other hand, my 1-2 target doesn't look so good because the POI started to wander down. I was shooting in 100 degree temps and what I have found is that after a number of shots in that kind of heat, POI does wander. I shot the >5 target first and the barrel was pretty hot by the time I shot my second target. Nonetheless, group sizes were smaller with the 1-2 ammo, but as you can see, the last two groups (at the bottom of the 1-2 target) were also the largest. I will have to do this test again, shooting the 1-2 first, then the >5.
Quantitatively, the average MOA for the >5 was 1.179 and the average MOA for the 1-2 was .969, so this number improved by 22% with sorting. I also measured average distance to center of the group. This number improved far more: from .443 MOA to .328 MOA, a 35% improvement.
From a statistical perspective, the improvement was less than 1 standard deviation, so the improvement was not statistically significant. Still, I think it is worth further investigation.
With better conditions, we might get a better comparison. I mentioned the high temps, but mirage was bad and windspeeds varied from 5 - 15 mph coming from 7 to 9 o'clock. Further, I just know from experience that groups are usually tighter from this gun.
My distribution looked like this:
Runout % of Population
0-1....... 2%
1-2....... 10%
2-3....... 19%
3-4....... 19%
4-5....... 18%
5&+....... 33%
These runout numbers are in thousandths of an inch. I could mention brand, but it is all made by CCI, so it doesn't matter. The bullet is V-Max.
Here are the targets
5 and up runout:
1-2 runout:
My >5 target doesn't look so bad because the POI is very centered. On the other hand, my 1-2 target doesn't look so good because the POI started to wander down. I was shooting in 100 degree temps and what I have found is that after a number of shots in that kind of heat, POI does wander. I shot the >5 target first and the barrel was pretty hot by the time I shot my second target. Nonetheless, group sizes were smaller with the 1-2 ammo, but as you can see, the last two groups (at the bottom of the 1-2 target) were also the largest. I will have to do this test again, shooting the 1-2 first, then the >5.
Quantitatively, the average MOA for the >5 was 1.179 and the average MOA for the 1-2 was .969, so this number improved by 22% with sorting. I also measured average distance to center of the group. This number improved far more: from .443 MOA to .328 MOA, a 35% improvement.
From a statistical perspective, the improvement was less than 1 standard deviation, so the improvement was not statistically significant. Still, I think it is worth further investigation.
With better conditions, we might get a better comparison. I mentioned the high temps, but mirage was bad and windspeeds varied from 5 - 15 mph coming from 7 to 9 o'clock. Further, I just know from experience that groups are usually tighter from this gun.
