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Topic: POI shift (Read 198 times) previous topic - next topic

POI shift

Hello all.. new to the forum.  I need some info from some of you more experienced shooters/reloaders.  I’ve just purchased a Bergara HMR 6.5CM.  I zeroed at 100 with 123 eldm’s.  It has sub half MOA groups, consistently out to 250yds with no horizontal poi shift.  So I thought I would try the 143gr ELDx precision hunters.  Low and behold, they group even better!  The only problem is that they print 1moa low and 1moa left at 100yds.  Now the 1 moa low doesn’t concern me as much as the left shift… now the question…. If it’s 1” left at 100, it will be even further left at 200, so on and so forth… right?  So even if I rezero to account for the left shift, it’ll still be left at 200.. right? Please forgive… there’s so much I’m trying to learn.. I’ve been told that the shift is due to harmonics/barrel whip…. How do I keep them all in vertical alignment with the bore axis, like the 123gr?

Re: POI shift

Reply #1
If you bring your “harmonic” left shift back to zero it will shoot straight on out at 200. 300, etc. You are right though - if you continue the 1” left at 100, it will be 2” out at 200, 3” out at 300, etc.

What you think you are seeing as a left shift with the 143 gr may just simply be a correction from a right shift you were getting with the 123 gr.

Re: POI shift

Reply #2
Welcome to the forum jculpepper.. its not uncommon for different bullets to have different poi's. Rezero the rifle and you should be good to go..
Grant

Re: POI shift

Reply #3
Thanks so much for your reply.  I have shot the 123gr, 140gr Norma, and 140gr federal.. all at distance.  The all stay on the same vertical axis.  Just either high or low.  It seems to just be the 143gr ELDx.  I just wish there was some way to get those to stay on that vertical axis as well.

Re: POI shift

Reply #4
What optic do you have on there?  Is it hard to re zero the windage?

Re: POI shift

Reply #5
@Jculpepper73

Factory ammo or reloads?

If you rezero it will be fine especially at hunting distances your question is interesting though and relates specifically to where your muzzle is in it's "whip" when the bullet exits the barrel.
If it's factory ammo you're stuck with it but as said rezero and shoot it.
Reloads can be tuned in some cases to leave the barrel in a better position in the whip.
When tuning handloads in a rifle we are finding that spot in the whip where the muzzle is most stable and when things are really right we can catch the whip on the bottom of it's oscillation and that lets the the faster bullets come out on the bottom of the cycle while the slower bullets exit on the upswing placing them closer to the faster rounds it's called positive compensation.

Dave

Re: POI shift

Reply #6
Positive compensation can also occur at the top of the barrel swing.

Re: POI shift

Reply #7
Sorry everyone. I am new to discussion form formats. I’m trying to figure out how to respond to each of you individually.

Optic: Arken SH4 4-16x50 (I personally mounted, leveled, torqued, loc-tite everything from base up.)

123gr ELDm are reloads that I worked up with Varget 39gr
140gr Norma factory
140gr Federal factory
143gr ELDx precision hunter factory

Also, I’m trying to attach pics of targets/grouping from iPhone but is not allowing jpeg pics. Figures..🤦🏻‍♂️


Re: POI shift

Reply #9
You just have to record on paper someplace, or on your phone,  the two different zeros. Once it is zeroed for either, it will stay. Just loosen the hex screws and zero the windage turret.

ELDX will have a separate windage zero that the rest, but once either is adjusted, you will be good to go. 4 clicks.

Re: POI shift

Reply #10
Sorry everyone. I am new to discussion form formats. I’m trying to figure out how to respond to each of you individually.

Optic: Arken SH4 4-16x50 (I personally mounted, leveled, torqued, loc-tite everything from base up.)

123gr ELDm are reloads that I worked up with Varget 39gr
140gr Norma factory
140gr Federal factory
143gr ELDx precision hunter factory

Also, I’m trying to attach pics of targets/grouping from iPhone but is not allowing jpeg pics. Figures..🤦🏻‍♂️

IMO that kind of proves my point the 123s were worked up in your rifle and zeroed the 143s are factory and not optimized for your gun even though they're shooting smaller. Zero the scope to the 143s but make note of the 123 zero so you can easily return to it.
Dave