OCW - powder charge vs. seating depth

[HobbyShooter]

I've been having a hell of a time trying to work out a powder charge using 175 smk's, IMR 4895, and Winchester brass. Looking at other people's OCW targets, it seems easy to find the charges that have the same general POI as well as the accuracy and scatter nodes, but when it came to my own targets, I've been grasping at straws.

I did all of my testing at .020" off the lands as the instructions state and was beginning to think it was either time to change powder, or give up on sub-MOA accuracy. I shot this target below at 100 yards and after doing my best to interpret the results, I decided on 42.0 grains as the charge to pursue. You can see a note on the top right where I adjusted the scope when my first OCW shot was off the target. A no-no, but I couldn't have half my data on the cardboard. At 41.1, I thought the scope was tracking poorly.

After deciding 42.0 was the best I was going to get, I shot tests at .030", .020", .010" off the lands, on the lands, and one group jammed .010" into the lands. The results were pretty clear that my rifle favored seating right at the lands. with a 1.21" group at 132 yards.

On a hunch, I shot another OCW test with all the rounds seated at the lands to see if 42.0 was still the charge to pursue. Much to my delight, I ended up with a target that was easy to interpret. I see an accuracy node at 41.4, and another near 42.6. A scatter node at 42.0 (where I previously thought my accuracy would be) and near 40.8. I'm picking 41.4 as my powder charge, not because it's smallest, but because the POI of 41.1 and 41.7 are pretty close to the POI of 41.4.

On a side note. 41.4 measures at .362" @ 132 yards which is pretty close to .25 MOA.

The long-winded point I'm trying to make, is it seems it may be best to figure out what seating depth a rifle prefers before working out powder charges.

Thoughts?

 

[Bob 964]

I conduct my OCW tests with the bullet seated at the depth at which the ogive touches the lands. Theoretically, this is a neutral depth --- the bullet is neither jammed nor jumped. Once I determine the OCW, I then load (at the OCW) and shoot five 5-round groups seated at 0.010" jammed (always start jammed), 0.030" jumped, 0.060" jumped, 0.090" jumped, and 0.120" jumped. Usually, one of these groups will perform significantly better than the others. From there, I can further refine my seating depth until I get the desired results. This is what works for me.

 

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I conduct my OCW tests with the bullet seated at the depth at which the ogive touches the lands. Theoretically, this is a neutral depth --- the bullet is neither jammed nor jumped. Once I determine the OCW, I then load (at the OCW) and shoot five 5-round groups seated at 0.010" jammed (always start jammed), 0.030" jumped, 0.060" jumped, 0.090" jumped, and 0.120" jumped. Usually, one of these groups will perform significantly better than the others. From there, I can further refine my seating depth until I get the desired results. This is what works for me.

This works well for me, it seems critical to find where the bullet likes to be seated.

 

[Dan Newberry]

I load 42.4 grains in all of my match and range ammo, which is often used in various .308's--and it shoots well in all of them.

What kind of rifle is this?

 

[HobbyShooter]

I load 42.4 grains in all of my match and range ammo, which is often used in various .308's--and it shoots well in all of them.

What kind of rifle is this?

.308 caliber Savage 11.

42.4 may work as well, although it seems it may still be coming off the scatter node and headed toward an accuracy node I'm guessing at 42.7.