Help explain this

[dreever]

Shooting off a Sinclair Competition front rest and Protektor rear bag my .308 using Berger 175 Tactical OTM's @2615 fps my come ups are as follows for these actual yardages:
100 yard =-0-
321 " =+ 5.1 MOA from zero
414 " = + 8.1 MOA "
542 " = + 12.8 MOA "
804 " = + 24.3 MOA "

Switching to a Harris bi-pod from the bench the change is as follows:

321 = +4.1 MOA
414 = +7.1 MOA
542 = + 11.3 MOA
804 = +23.1 MOA

Somethings going on but what??????

 

[Bryan Litz Ballistics]

It's not uncommon for the rifle rest to affect zero. My Palma rifle is not zeroed when I shoot it off of a rest, but when I shoot it from a sling it centers up at the same range. The zero shift is about one MOA depending on what's supporting the rifle.

Rifles with shorter stiffer barrels tend to have their zeros less affected by their support.

When zeroing a long-range rifle, it's important to zero it from the position that you're most likely to shoot long-range from. If you zero on a benchrest pedestal, and do most of your LR shooting off a Harris bipod in the prone position is a bad idea. This is what you're seeing.

 

[dreever]

Thanks Bryan,

Off the rest my zero's were almost identical to both Berger's and JBM ballistic programs. Not so with the bipod. The further out I went the more drastic the difference. That's why I was scratching my head.
As to the weird yardages I had a friend who's a surveyor shoot the actual distances for me. Big difference from what I originally thought they were.

Danny

 

[DMONEY]

It's not uncommon for the rifle rest to affect zero. My Palma rifle is not zeroed when I shoot it off of a rest, but when I shoot it from a sling it centers up at the same range. The zero shift is about one MOA depending on what's supporting the rifle.

Rifles with shorter stiffer barrels tend to have their zeros less affected by their support.

When zeroing a long-range rifle, it's important to zero it from the position that you're most likely to shoot long-range from. If you zero on a benchrest pedestal, and do most of your LR shooting off a Harris bipod in the prone position is a bad idea. This is what you're seeing.

so any change to angle of attack ...can effect zero ... never thought about that

 

[jcampbellsmith]

dreever

One quick question. Did you reconfirm your 100 yd zero when you changed over to the bipod?

Thanks

JCS

 

[XTR]

Any chance the bipod is supporting the rifle further out on the end of the stock and you are getting flex and contact between the stock and barrel on recoil?

 

[alf]

Switching to a Harris bi-pod from the bench.

Somethings going on but what?

Try putting a piece of carpet under the legs.

 

[Jason Boersma]

Bipods bounce a little bit so your going to shoot a little different than on a rest