POI shift with scope magnification?

[Beuford T. Rimfire]

While shooting this morning I decided to play around with different magnifications on my new scope. I just bought a Primary Arms 1x-4x scope and mount a few weeks ago and zeroed it last weekend using only the 4x power. Today, it shot very true at 25 yards on 4x - shooting at 1/2" dots most 3-5 shot groups were nickle sized minus the occasional flyer or pulled shot, all done with Winchester M-22.

When I would move to a different power my groups would shift up about an inch and shift slightly to the right. Only POI changed, my consistency and group sized remained fairly unchanged. Maybe this is normal to not be exactly zeroed at all powers in a scopes range, but on such a small difference in magnification, I wouldn't think that it would make a lot of difference in this case. On other rimfire rifles I have, I usually zero on about 7x for a 3x-9x scope and have never noticed much difference but I rarely deviate from 7x by more than 1 or 2x in either direction.

Anyone have a good explanation for this? I shot plenty of rounds, plenty of patterns at different magnifications, so I'm fairly certain that this isn't an error in my shooting form.

 

[Fishinfool]

I have had the same issue with several scopes I have owned in the past.

Its not uncommon for inexpensive scopes to change POI with power changes, or to lack accuracy and repeatability when making elevation and windage adjustments. Some more so then others.

That's a couple of the hidden benefits to brands like Leupold when people say they cant see spending more money when both scopes look about the same...

I hear Primary Arms has decent customer service. I would call them, and describe the problem. They may replace your scope for you.

 

[MarkBrumbaugh]

Make sure it isn't parallax.

 

[Beuford T. Rimfire]

Make sure it isn't parallax.

I wouldn't be surprised if it was. If my cheek weld is consistent, yet slightly out of center of the reticle that might explain my POI shift. Any tips for dealing with parallax error on non-AO scopes? (always shoot on 4X? )

 

[MarkBrumbaugh]

I wouldn't be surprised if it was. If my cheek weld is consistent, yet slightly out of center of the reticle that might explain my POI shift. Any tips for dealing with parallax error on non-AO scopes? (always shoot on 4X? )

Only thing is to modify your stock or get a different scope. I mount my scope by closing my eyes and then opening. If I don't see an even shadow around the target when the scope is forward, before tightening, I know I'm going to have a problem. I think there is a good thread on rimfire central on scope mounting.

 

[Alan Roberts]

... I think there is a good thread on rimfire central on scope mounting.

Mark, I struggle to find the time to keep up with this forum! Rimfire central is a huge collection, are you referring to one of the sticky posts in the Scopes, Rings, Mounts ... forum or a post elsewhere?

Thanks,
Alan Roberts

 

[MarkBrumbaugh]

I googled correct way to mount a scope

 

[MarkBrumbaugh]

Copied from another forum, another poster...
Close your eyes and pick the gun up and put in the position that feels the best to you. Without moving the gun, open your eye, DO NOT TRY TO LOOK THROUGH THE SCOPE. What is your eye looking at?

If you are looking at the top of the eyepiece of your scope, you need taller rings.

If you are looking at the bottom of the eyepiece, you need shorter rings.

If you are looking at the right side of your eyepiece, you need to pad your cheekpiece.

If you are looking at the left side, you need to do some woodworking.

+1

If your only complaint with the current scope is parallax, then follow Fjold's advice. Make the mods needed to get the stock and scope rings working for you. If you can get your cheek weld spot on and center your eye in the sight picture every time, then you don't need adjustable parallax. It's only for people who can't - or don't want to take the time - to center their eye.

Also, make sure you have the scope properly positioned along the receiver. Repeat the exercise that Fjold described using your likely shooting position (standing, sitting, prone, etc.). This time notice if you have to move your head forward or backward to see the edges of the field of view. You want the eye as far back as possible without loosing the edges of the field of view. Move the scope forward or backward relative to the receiver so that your natural cheek weld puts your eye right at the optimum eye relief. If you have a hard-kicking rifle (more than 30-06), then move the scope forward another 0.5-1" from optimum. I've had to do this when shooting .50 BMG to keep the scope from dinging my forehead.

 

[Beuford T. Rimfire]

Thanks, Mark! I'll give all these points some concideration. With the scope being newly mounted to my rifle, I do know that the eye relief could use some adjustment to be in a more intuitive position.