P.O.I. Moving to Right?

be2man

be2man

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Sorry if this is a Newb question. I'm trying to find a good factory load for my Benelli MR1, which is admittedly not a precision rifle. The best so far has been the Federal 55gr Nosler Ballistic tip. About 1-1.5 MOA. Several other loads I've tried -American eagle, PMU-55gr FMJ, Win 62gr FMJ and Federal 62gr match HP'S, all group consitently to the right 4-8" at 100 yards. The barrel is 20" with a 1:9 twist.
My question is what factor/factors cause the POI to move laterally. I would expect it to be high or low depending on loading and bullet weight but curious as to causes of lateral movement.
Thanks
 
be2man said:
Sorry if this is a Newb question. I'm trying to find a good factory load for my Benelli MR1, which is admittedly not a precision rifle. The best so far has been the Federal 55gr Nosler Ballistic tip. About 1-1.5 MOA. Several other loads I've tried -American eagle, PMU-55gr FMJ, Win 62gr FMJ and Federal 62gr match HP'S, all group consitently to the right 4-8" at 100 yards. The barrel is 20" with a 1:9 twist.
My question is what factor/factors cause the POI to move laterally. I would expect it to be high or low depending on loading and bullet weight but curious as to causes of lateral movement.
Thanks
Click to expand...

When you change ammunition you are changing pretty much all of the components. Different manufacturers use different powders, bullets, primers, brass etc. Thus they will all have a different point of impact.
Also certain ammuntion produces different vibrations (harmonics) in the barrel which also creates a different point of impact. Pick one brand of ammunition that shoots well and stick with it. Sight the rifle in with that ammo and leave it. Changing different brands will require you to sight it in all over again.
 
Jeromeo said:
When you change ammunition you are changing pretty much all of the components. Different manufacturers use different powders, bullets, primers, brass etc. Thus they will all have a different point of impact.
Also certain ammuntion produces different vibrations (harmonics) in the barrel which also creates a different point of impact. Pick one brand of ammunition that shoots well and stick with it. Sight the rifle in with that ammo and leave it. Changing different brands will require you to sight it in all over again.
Click to expand...

Thanks, The downside is the best loads are $37 a box, which is fine for hunting. I had hoped I could find a reasonably priced FMJ load that I only had to adjust vertically for "fun" target shooting but not happening yet. I guess reloading at some point is the answer.
I was questioning the physics that would cause lateral movement but many variables as you point out.
 
Does the group walk over to the right a bit further with each shot, or do your shots all fall in a group further right than a group shot with different ammo.

In the case of the former, it is either wind or the fact that your barrel is changing dimensionally as it heats up... a not-so-uncommon problem with barrels that have not been fully stress relieved, asymetrically fluted, or made of steel with poor homogenicity.

In the case of the latter, harmonics, spin of the bullets, and other voodoo $hit for which there is no earthly explanation. The bright side of this is you always have a good excuse, and one which we will all believe.
 
With my Savage .308, if I use IMR 4064 there is a .5 MOA to the left change from Varget. Make note if you are using more than one round so you can quickly and easily adjust.
 
Obtunded said:
Does the group walk over to the right a bit further with each shot, or do your shots all fall in a group further right than a group shot with different ammo.

In the case of the former, it is either wind or the fact that your barrel is changing dimensionally as it heats up... a not-so-uncommon problem with barrels that have not been fully stress relieved, asymetrically fluted, or made of steel with poor homogenicity.

In the case of the latter, harmonics, spin of the bullets, and other voodoo $hit for which there is no earthly explanation. The bright side of this is you always have a good excuse, and one which we will all believe.
Click to expand...

The gun does shoot pretty well for what it is with the Federal 55gr Nosler BT
This was a couple of 3 shot groups working on sighting in after 15 or so shots so barrel was warm. Shot the group on the right first, moved scope 4 clicks left and shot group on the left. Second pic is scope back 2 clicks right.
Want to be 1.5" high at 100 yard with this load.
The movement and opening up of the groups with other ammo seemed to be consistent and consistently right.

IMG00088-20110207-1517.jpg


IMG00089-20110207-1517.jpg
 
I'd rule out the scope first.
Watch your scope tracking thru a bore sight.
After your done making an adjustment give it a thump and see if it moves again.
 
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