CFJunkie
09-15-2019, 11:28 AM
I often see posts on different forums that list 3 round group results that get pretty severe comments about how 3 round groups are not indicators of load performance and they shouldn’t be use to compare results and that 5 round groups are the standard of comparisons. Others claim that I would generally agree with that, especially if the poster is basing conclusions on just one or two groups. Others have said they use 3 round groups for load development because once 3 rounds show poor results, the next to shots aren’t making the group any better.
I have been using 3 round groups for development for years, simply because it is cheaper but I also shoot lots of groups to verify my conclusions as you can see from the table immediately below for some of my better shooting rifles.
6297
I also shoot 5 round groups that I use in the data I post on this forum. The resulting averages are larger largely because of shooter induced variations that cause successive shoots to open up groups. The best groups are still about the same size but there are fewer of them and some of the groups grow with the two extra rounds so the average is larger. I accept that that is caused by the shooter, not the rifle and don’t make excuses for that.
6298
However, I thought you would like to see the comparison of the results to see how much larger the 5-round groups are than the 3 round groups. The ratios compare the overall group averages for the 5 to 3 round groups and the 3 to 5 round groups.
6299
The ratios for each caliber are surprisingly similar but the heavier caliber .308s actually have better ratios showing that the 3-round overall average group sizes are closer in size to the 5-round overall average group sizes than for the .223 or 6.5mm Creedmoor rifles. The differences are the smallest for the high calibers and the largest for the lightest calibers. That seems counter intuitive considering that the recoil is heavier in the larger calibers, but it may simply indicate that the 3-round groups for the higher calibers are more effected by recoil so the 3-round group averages for the higher caliber rifles is larger but the ‘shooter induced variations’ that grow the groups when shooting the last two rounds are about the same, regardless of caliber.
Surprisingly, the Savage 10 FCP-K .308 data is heavily biased by 175 to 200 grain bullet loads which have a stronger felt recoil than the lighter 150 to 168 grain .308 bullets that dominate the data for the Savage 10 FP .308, which incidentally has a heavier stock to further eliminate recoil. The 10 FCP-K is the only rifle that has a muzzle brake. All the other rifles have no flash hiders or muzzle brakes.
In the notes following these two tables, I have tried to add information that would make it clearer why there are differences in the relationships of the overall averages and the Top 20 and Top 10 load averages between some of the rifles that appear to have better averages for their top 25 and Top 10 loads than for their overall averages. Basically, the overall data shows the results for all the loads used in development, even the ones that were very inaccurate. In the case of the 6.5mm Creedmoor rifles, the newer rifles got the benefit of being able to avoid the inaccurate powder bullet combinations.
Notes:
The Les Baer Super Varmint .223 overall average is severely skewed by poorer performance with the original stock (A2) that was too short for me and caused vertical stringing. After changing the stock, the groups improved significantly as is apparent in the top 25 and top 10 load averages. The top 25 loads are all 69 and 77 grain bullets shot with a Magpul adjustable match stock and ar a better indicator and comparator of the rifle's performance
The Savage 12 12 FV .223 overall average is skewed by poorer performance with bullets weights under 60 grains. The best performance is with 69 and 77 grain bullets (even though the barrel twist is 1:9). All the Top 25 and Top 10 loads are composed of 69 and 77 grain bullets.
The Savage 12 LRP 6.5mm Creedmoor was my initial rifle in that caliber and was used for load development to find what worked best. The 12 FV was a later addition with the same barrel length and only shot the loads that were the 12 LPR best performers. The Top 25 loads show the 12 LRP is the better performer with the better performing bullets and powders.
The Savage 10 FP and 10 FCP-K perform almost identically, but the FP prefers bullets in the 150 to 168 grain weight range and the 10 FCP-K prefers bullets in the 168 to 200 grain weight range. The overall average of the 10 FCP-K is slightly skewed by my unwillingness to accept that the 10 FCP-K didn't shoot the lighter bullets as accurately. the 5-round group averages for the 10 FCP-K .308 are actually smaller than the similar averages for the 10 FP .308. I didn’t shoot 5 round groups until I was relatively sure of what performed well.
The Savage 10T-SR has a 24-inch barrel so the loads were different than the 26-inch barrel model 12 LRP in the same caliber. After some load development with the 10T-SR that required a totally different load philosophy to match the different barrel reflection time, I found a 26-inch 12 FV that could become the load development platform for the more expensive 12 LRP and I stopped load development on the 10T-SR.
I have been using 3 round groups for development for years, simply because it is cheaper but I also shoot lots of groups to verify my conclusions as you can see from the table immediately below for some of my better shooting rifles.
6297
I also shoot 5 round groups that I use in the data I post on this forum. The resulting averages are larger largely because of shooter induced variations that cause successive shoots to open up groups. The best groups are still about the same size but there are fewer of them and some of the groups grow with the two extra rounds so the average is larger. I accept that that is caused by the shooter, not the rifle and don’t make excuses for that.
6298
However, I thought you would like to see the comparison of the results to see how much larger the 5-round groups are than the 3 round groups. The ratios compare the overall group averages for the 5 to 3 round groups and the 3 to 5 round groups.
6299
The ratios for each caliber are surprisingly similar but the heavier caliber .308s actually have better ratios showing that the 3-round overall average group sizes are closer in size to the 5-round overall average group sizes than for the .223 or 6.5mm Creedmoor rifles. The differences are the smallest for the high calibers and the largest for the lightest calibers. That seems counter intuitive considering that the recoil is heavier in the larger calibers, but it may simply indicate that the 3-round groups for the higher calibers are more effected by recoil so the 3-round group averages for the higher caliber rifles is larger but the ‘shooter induced variations’ that grow the groups when shooting the last two rounds are about the same, regardless of caliber.
Surprisingly, the Savage 10 FCP-K .308 data is heavily biased by 175 to 200 grain bullet loads which have a stronger felt recoil than the lighter 150 to 168 grain .308 bullets that dominate the data for the Savage 10 FP .308, which incidentally has a heavier stock to further eliminate recoil. The 10 FCP-K is the only rifle that has a muzzle brake. All the other rifles have no flash hiders or muzzle brakes.
In the notes following these two tables, I have tried to add information that would make it clearer why there are differences in the relationships of the overall averages and the Top 20 and Top 10 load averages between some of the rifles that appear to have better averages for their top 25 and Top 10 loads than for their overall averages. Basically, the overall data shows the results for all the loads used in development, even the ones that were very inaccurate. In the case of the 6.5mm Creedmoor rifles, the newer rifles got the benefit of being able to avoid the inaccurate powder bullet combinations.
Notes:
The Les Baer Super Varmint .223 overall average is severely skewed by poorer performance with the original stock (A2) that was too short for me and caused vertical stringing. After changing the stock, the groups improved significantly as is apparent in the top 25 and top 10 load averages. The top 25 loads are all 69 and 77 grain bullets shot with a Magpul adjustable match stock and ar a better indicator and comparator of the rifle's performance
The Savage 12 12 FV .223 overall average is skewed by poorer performance with bullets weights under 60 grains. The best performance is with 69 and 77 grain bullets (even though the barrel twist is 1:9). All the Top 25 and Top 10 loads are composed of 69 and 77 grain bullets.
The Savage 12 LRP 6.5mm Creedmoor was my initial rifle in that caliber and was used for load development to find what worked best. The 12 FV was a later addition with the same barrel length and only shot the loads that were the 12 LPR best performers. The Top 25 loads show the 12 LRP is the better performer with the better performing bullets and powders.
The Savage 10 FP and 10 FCP-K perform almost identically, but the FP prefers bullets in the 150 to 168 grain weight range and the 10 FCP-K prefers bullets in the 168 to 200 grain weight range. The overall average of the 10 FCP-K is slightly skewed by my unwillingness to accept that the 10 FCP-K didn't shoot the lighter bullets as accurately. the 5-round group averages for the 10 FCP-K .308 are actually smaller than the similar averages for the 10 FP .308. I didn’t shoot 5 round groups until I was relatively sure of what performed well.
The Savage 10T-SR has a 24-inch barrel so the loads were different than the 26-inch barrel model 12 LRP in the same caliber. After some load development with the 10T-SR that required a totally different load philosophy to match the different barrel reflection time, I found a 26-inch 12 FV that could become the load development platform for the more expensive 12 LRP and I stopped load development on the 10T-SR.