echo3mike
Member
I've posted previously regarding the Optimum Charge Weight (OCW) Method , and thought I'd post some results from a test I did recently.
OCW stems from the idea that there are certain charge weights in certain powders that give uniformly excellent results in multiple rifles regardless of other componants, seating depth, or case prep; a case in point being FGM's or Black Hill's .308 Match ammo. It represents a range of weights often seperated by 0.5gr or more. The criteria for appropriate load selection is measured by POI and MV.
Since I recently switched some componants, I thought I'd try the method for my .308 with some 175gr SMKs and Varget. I've read on other boards how good this combination was (esp with CCI-BR2 primers). After some initial trial and error testing, I loaded six groups of three rounds, each group having a different charge weight. The weights were:
1) 43.5gr
2) 43.8gr
3) 44.1gr
4) 44.4gr
5) 44.7gr
6) 45.0gr
NOTE: the 45.0gr Varget / 175gr load represents the MAXIMUM LOAD from the Hogdon manual.
I used Lapua cases fired in the test rifle (700 VS 26" bbl) with extraneous case prep, CCI-BR2 primers, Sierra 175gr MK seated to a COL of ~2.800 (with a comporator the OAL was 3.155"). The 100 yd range where I shot the tests was 54 degrees F, 30.20 inHg, 29 % Hum, winds to 5mph from 6:00.
The test loads were shot in a "round-robin" fashion...I'd shoot a round from the first charge weight at one of six targets, then I'd wait two minutes and shoot a round from the second charge weight at the second of six targets, wait two minutes, shoot the third charge weight round at the third of six targets, etc. After the first group was shot, the second round from the first load was fired at the first of the six targets, the second of the second group at the second target, etc. The point of this is to eliminate some of the variances possible with excessive bore fouling before the later groups are fired, and to make recording the data easier. The acutal group size of any given load isn't irrelevent, but it's reliability as a testing criteria isn't weighed as highly as POI correlation and MV. Often, the load giving the smallest group doesn't meet the established criteria: in this test, the 43.8gr load produced a group of 0.302", a rifle low group. 3 fouling shots were used prior to load testing. Chronograph was used during the test for MV data.
RESULTS:
POI data suggested that the 44.1gr, 44.4gr, and 44.7gr loads shared roughly the same POI more consistantly than loads from other groups. In the first group of shots, these three loads had a POI of within 0.20". The second and third groups were larger, but still suggested that these three loads were exiting the barrel at close to the same point in the harmonic vibration, (node).
Chronograph data also suggests that the above mentioned three load weights had a high correlation. Data was found to be:
1) 43.5gr: 2701fps
2) 43.8gr: 2697fps
3) 44.1gr: 2712fps
4) 44.4gr: 2708fps
5) 44.7gr: 2713fps
6) 45.0gr: 2728fps.
There were no signs of excessive pressure or fouling.
While many may point out that three may not be an adequate test paradigm, the fact that loads very close to these have achieved excellent results in other rifles tends to lend some credence to the method.
S.
Warning: Always consult established loading manuals and work your charges up from lower weights. Watch for signs of excessive pressure. Wear eye and ear protection when performing this or any other testing method. Call your mom. Always practice firearm safety. Eat your vegetables. The author excepts no responsibility for damages occuring during the replication of this or any other testing methods.
OCW stems from the idea that there are certain charge weights in certain powders that give uniformly excellent results in multiple rifles regardless of other componants, seating depth, or case prep; a case in point being FGM's or Black Hill's .308 Match ammo. It represents a range of weights often seperated by 0.5gr or more. The criteria for appropriate load selection is measured by POI and MV.
Since I recently switched some componants, I thought I'd try the method for my .308 with some 175gr SMKs and Varget. I've read on other boards how good this combination was (esp with CCI-BR2 primers). After some initial trial and error testing, I loaded six groups of three rounds, each group having a different charge weight. The weights were:
1) 43.5gr
2) 43.8gr
3) 44.1gr
4) 44.4gr
5) 44.7gr
6) 45.0gr
NOTE: the 45.0gr Varget / 175gr load represents the MAXIMUM LOAD from the Hogdon manual.
I used Lapua cases fired in the test rifle (700 VS 26" bbl) with extraneous case prep, CCI-BR2 primers, Sierra 175gr MK seated to a COL of ~2.800 (with a comporator the OAL was 3.155"). The 100 yd range where I shot the tests was 54 degrees F, 30.20 inHg, 29 % Hum, winds to 5mph from 6:00.
The test loads were shot in a "round-robin" fashion...I'd shoot a round from the first charge weight at one of six targets, then I'd wait two minutes and shoot a round from the second charge weight at the second of six targets, wait two minutes, shoot the third charge weight round at the third of six targets, etc. After the first group was shot, the second round from the first load was fired at the first of the six targets, the second of the second group at the second target, etc. The point of this is to eliminate some of the variances possible with excessive bore fouling before the later groups are fired, and to make recording the data easier. The acutal group size of any given load isn't irrelevent, but it's reliability as a testing criteria isn't weighed as highly as POI correlation and MV. Often, the load giving the smallest group doesn't meet the established criteria: in this test, the 43.8gr load produced a group of 0.302", a rifle low group. 3 fouling shots were used prior to load testing. Chronograph was used during the test for MV data.
RESULTS:
POI data suggested that the 44.1gr, 44.4gr, and 44.7gr loads shared roughly the same POI more consistantly than loads from other groups. In the first group of shots, these three loads had a POI of within 0.20". The second and third groups were larger, but still suggested that these three loads were exiting the barrel at close to the same point in the harmonic vibration, (node).
Chronograph data also suggests that the above mentioned three load weights had a high correlation. Data was found to be:
1) 43.5gr: 2701fps
2) 43.8gr: 2697fps
3) 44.1gr: 2712fps
4) 44.4gr: 2708fps
5) 44.7gr: 2713fps
6) 45.0gr: 2728fps.
There were no signs of excessive pressure or fouling.
While many may point out that three may not be an adequate test paradigm, the fact that loads very close to these have achieved excellent results in other rifles tends to lend some credence to the method.
S.
Warning: Always consult established loading manuals and work your charges up from lower weights. Watch for signs of excessive pressure. Wear eye and ear protection when performing this or any other testing method. Call your mom. Always practice firearm safety. Eat your vegetables. The author excepts no responsibility for damages occuring during the replication of this or any other testing methods.
