changes to point of impact with neck tension

[jelenko]

This round-robin neck tension test was shot yesterday afternoon at 600 yards in Western Colorado, mid 30’s, cloudy, for us- light winds.
View attachment 1511329
I plan to go out and retest to verify
But thought I would share this one because you can clearly see how the point of impact changed with small changes in neck tension.

This was shot round-robin……… a 12 shot string.
Each bullet hole has the shot number written beside it.

For example the the yellow group is the three shots where I used a forester die with a 260 honed neck and inserted a .238” mandrel into the case neck, the shots were the 2nd, 6th, and 10th shots in the series of 12 shot fairly fast.

CW

Do I have it right that the distance from the center of the yellow group to the center of the blue group is just under 3.5"?

Thanks

 

[Mulligan]

Do I have it right that the distance from the center of the yellow group to the center of the blue group is just under 3.5"?

Thanks

I suppose where middle really is matters.

But you are close

It’s real and it is far enough away that you could go from HERO to ZERO in one shot if the neck tension is fouled up.

CW

 

[jelenko]

The reason I asked is I've been chasing an accuracy issue. It's only at 100 yards, but I happen to know my neck tension varies by ~ 2/1000 [223]. [The brass was processed by someone else]
I've been thinking the variation in neck tension wouldn't be noticed when looking for groups < 3/4 MOA. But, now I'm not so sure.
Ran a bunch of the cases through the just the neck sizing part of a FL die. I'll see tomorrow if it makes a difference. [When I do the resizing the variance in neck tension is far less than .25/1000. ]