.256 Newton load development

[rhocutt]

I fired this target from 150 yards resting on sand bags. I am trying to determine the most accurate load using 125 grain Nosler Partition bullets. This first trial was 9 rounds with IMR 4831 with charge weights increasing by 0.3 grains each round. The starting charge (round #1) was 47.9 grains and round #9 was 50.3 grains. I don't have a chronograph so velocities are unknown.

I was surprised that the vertical separation was so distinct, and surprised also that round 6 printed at the same elevation as round 1.

So I'm not exactly sure how to interpret these results or exactly where to go from here. I would like to know any comments or suggestions the community may have.

 

[ants]

How much time between shots? Barrel heat can change point of impact
for many rifles, especially if the barrel is not free floating.

None of them seem to be bad fliers, I think you're on the right track.

0.3 grains is a good choice between charges, 0.5 grains also acceptable.
Your spread of charge weights is good, now go back and do a full test.

Best to do 5 shots at each charge weight. In addition to point of impact,
you are looking for the nicest tightest group you can achieve.
This group looks about 4" at 150 yards. Cut that in half. Maybe less.

Ken Waters (back in 1987) tested several bullets and powders.
125 grain Nosler Partition was best with Win 760 (47.0 grains 2833fps)
and it was reported as one of his two best all around loads.
IMR4831 he reported 50.0 grains as "near maximum" so your 50.3 is tops.
He also used 129 grain Hornady spire point with IMR 4350 for the other
best all around load.

 

[rcmodel]

Well, unless you are a championship level rifleman able to call every shot without looking at it??

No way can you tell anything by just shooting one shot with each load.

You need to shoot at least 3-shot groups, but preferably 5 or 10 shot groups with each load to rule out operator error as much as possible.

rc

 

[sage5907]

If that was my shooting I would analyze it as follows. Shot 1 was from a clean barrel which caused it to shoot low and maybe left. Shots 2, 3, 4 and 5 is my best load range for that powder/bullet combination. For shots 6, 7, 8 and 9 either the barrel heated up, the rifle didn't like the hotter loads, or I lost concentration and couldn't hold the rifle still and on the same point of impact. As a final point, go back and read what rcmodel said.

 

[rhocutt]

Thanks for your comments and suggestions. I can see I have more work to do on it. I think I am going to start over.