load test question

[savage308]

i was working up a load for a new bullet and found something strange
the gun is a 308win 24"barrel and the bullet is 168 nosler custom comp, win LR primers, fed cases, IMR 8208 powder
i started with 39.5 and increased 2 tenths grains for each shell untill the max of 43.7
the first shot was the 39.5 and it was 2" low but center of target the as the load increased the impact kept getting lower
by about a half inch each shot all the way to the 43.7. i expected the impacts to be higher each shot .is this normal?

[Lloyd Smale]

bullet is spending less time in the barrel as it recoils.

[savage308]

i thought about that too. i was using a lead sled with 40 pounds of lead ingots but i didnt have the gun strapped down
so the recoil was letting the muzzle rise so that must be it .thanks

[shot1]

Yep. The bullet is going faster with each increase of the powder charge and spending less time inside the barrel as the rifle rises in recoil thus the bullet is striking at a lower point of impact.

It has been my experience that people using those lead sleds find that when they zero their rifle in using one that their point of impact/zero will change when the go to shooting it off their shoulder. Same principle you are finding with the different powders. The recoil is handled differently in the lead sled than it is when you shoot off your shoulder.

[Halwg]

It's interesting because I have had the exact opposite happen.  I have had slower loads print to a higher POI than faster loads.  All do to barrel harmonics.

[cwlongshot]

Thats the way it works..

Slower bullets impact higher on the target, faster ones strike lower.

Just yesterday, while shooting my 500 S7W handi, it was painfully apparent... Top loads struck near POA, but the lighter lead loadings where 3-4" high and the powder puff 1100 fps Trail Boss loadings hit almost a foot high at fifty yards.

CW

[necchi]

With all that,
 Why? When I run a ladder test at 200 with progressively increased charges, do the impact points rise on the target?