magnification affects impact zone?

[ok.lr-hunter]

tl.dr: My current setup is easily capable of 1 m.o.a. three shot groups at low to mid magnifications, but on higher magnification the grouping explodes to 4 or maybe 5 m.o.a. What is going on?
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So I'm a long time hunter, but new to long range shooting and new to this forum too. This year I decided to start dabbling into long range shooting, with an aim to eventually do some long range hunting. I bought a project rifle with the intention of re-barreling and changing the caliber (that's a discussion for another time). I unwisely spent most of my budget getting a rifle with the features I wanted and that would allow me to change to the caliber I intended. So I started looking into a budget scope that would be good enough to shoot out to 500 yards maybe further with lots of practice. I came across a YouTube video about the Shepherd Rogue scope and I took a gamble on it.

In my initial research I read somewhere the ideal magnification for the scope, a Shepherd Rogue 6-24x50mm was at 22 power. So we mounted it to the gun, bore sighted it, did an initial sight in at about 20 yards and then went back to 100 yards. At this point thanks to some bad premium ammo we had to stop. I wound up having to disassemble the bolt to remove pieces of the primer that had blown back into the bolt and were affecting the firing pins ability to strike consistently. A week later we were back at it trying to dial in the group at a 100 yards but we were chasing it all over the place. It was about that time the ticks were getting bad at our private range and I had to put it aside for a while.

Fast forward to this past weekend. I wanted to make sure the internals were square and level so I printed off an image of some crosshairs leveled and hung them a distance a way and put my rifle into my gun vise and leveled it. I reduced the power to 6 since I was working in my house. Everything checked out. I was still iffy, but I needed to double check my usual deer rifle, so I loaded them both up with a full load out of equipment and went to the range. dialed in my deer rifle, and then the big moment came and I threw the project rifle up there, remounted the scope and hit the high right edge of the bullseye off the bat. Two rounds later I had a three round 1 m.o.a. group. I dialed it up to 24, took another shot and it landed about 3 inches high and right.

I've done enough research to know that at higher magnifications groups tend to grow a little bit (like growing from 1 to 1.3 m.o.a.) because every movement is more visible, but from 1 to 3 m.o.a. just by changing magnification? I just don't know what's going on. I fired off several more rounds at high magnification and they were all over the target. So here I am on the forums asking for suggestions, tips, ideas, really anything. I've also fired off an inquiry to the manufacturer to see what they think.

Setup:
2018 Savage 110 long range hunter in 7mm Rem Mag
Shepherd Rogue scope 6-24x50mm
TPS TSR Picatinny-Style Riflescope Rings 30582
EGW 20MOA Savage Round back Picatinny Scope rail
Federal Deer Thug 160gr ammunition

 

[dok7mm]

The first warning would be "gun vise". They tend to be rough on scopes. Also, I am not familiar with the quality of your scope, but it could be it's not tracking or is slipping in rings. I would remount and check all screws for torque, in base & rings. If everything is tight, I'd look at scope as being the culprit.

 

[ok.lr-hunter]

The first warning would be "gun vise". They tend to be rough on scopes. Also, I am not familiar with the quality of your scope, but it could be it's not tracking or is slipping in rings. I would remount and check all screws for torque, in base & rings. If everything is tight, I'd look at scope as being the culprit.

Yeah, when we took it out this weekend we remounted it and checked everything for proper tightness. Also when I dial the magnification back down, from 22 to 14 for example, the group goes back down to 1 m.o.a. So you think it is something wrong with the scope then?

 

[ShtrRdy]

From what you're saying it sure sounds like a scope problem. Are you shotting off sandbags or some sort of rest?

 

[dok7mm]

3" right sounds like it's not level to bore or you're canting the scope. Can't speak as to group size. Have you tried shooting off bags? Rate of fire, is barrel getting hot. Too many possibilities to troubleshoot it online.

 

[ok.lr-hunter]

From what you're saying it sure sounds like a scope problem. Are you shotting off sandbags or some sort of rest?

All rounds are being fired from a bench using a set of Caldwell deadshot bags.

 

[ShtrRdy]

You might try setting up the rifle in your bags and have it pointing at some target. Then tap on the scope to see if the reticle jumps around.

Or, .... something else to try is mounting this scope on a known good shooting rifle. It could be a 22 even. Then try shooting a few groups at different scope power settings.

It looks like Shepherd has a lifetime warranty to original owners. You could send it in and have them check it out.

 

[ok.lr-hunter]

3" right sounds like it's not level to bore or you're canting the scope. Can't speak as to group size. Have you tried shooting off bags? Rate of fire, is barrel getting hot. Too many possibilities to troubleshoot it online.

When we originally installed everything we had so many levels to make sure the scope was level to the mounting rail that it was almost silly. I'm reasonably certain that it is level.

I also have an anti-cant level on the rifle to help prevent me from canting, though at a hundred yards I've never seen that much variation in any of my rifles due to cant at that range.
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It was pretty cold this weekend so I left the action open and gave a couple minutes between each group of three. I tried to eliminate as many variables as possible.

 

[cohunt]

What distance is it zeroed at and what powder did you use to zero it?
Then next question, what distance are you shooting at when you notice the enlarged groups?

 

[ok.lr-hunter]

One thing I forgot to mention is before we put it away we dropped one of my cousin's nightforce scopes on the rail and after a couple of rounds and some adjustments we had it dialed in. The rifle is definitely known good.

 

[ok.lr-hunter]

What distance is it zeroed at and what powder did you use to zero it?
Then next question, what distance are you shooting at when you notice the enlarged groups?

Zeroed at 100 yards, and I'm using factory loaded ammunition (Federal 160gr Deer Thug Ammo) for now to build up a nice pool of brass for reloading. The rifle shoots great at 6 and 14 power for sure. No change in distance, the only change is pushing the magnification up to 22/24 and that makes the grouping increase exponentially.

 

[dok7mm]

I misread that it was in a gun vice, only for leveling, sorry. If the NF didn't throw groups, like the Shepard, sounds more like scope tracking.

 

[Hand Skills]

That's an interesting problem. I wouldn't spend too much time trying to sort it out - you have a good description of what's happening - time to test out the warranty department.

It's actually a pretty common problem for POI to change with magnification in scopes with a reticle in the second focal plane (SFP), but POI shift is not the same as the scattergun effect you are seeing.

Could be mechanical - the erector housing is too big for the erector assembly at one end - manufacturing tolerances? Missing a bushing? Who can say.

Could be an optical problem causing parallax?

Any chance of returning it for store credit?

 

[ok.lr-hunter]

That's an interesting problem. I wouldn't spend too much time trying to sort it out - you have a good description of what's happening - time to test out the warranty department.

It's actually a pretty common problem for POI to change with magnification in scopes with a reticle in the second focal plane (SFP), but POI shift is not the same as the scattergun effect you are seeing.

Could be mechanical - the erector housing is too big for the erector assembly at one end - manufacturing tolerances? Missing a bushing? Who can say.

Could be an optical problem causing parallax?

Any chance of returning it for store credit?

Unlikely on the store credit, but there shouldn't be an issue with sending it back for warranty repair.