Scope shadowing and group size

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lowmileage

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Hi all,
I was guilty the other day of "scope shadowing." To those uninformed, which included me and I've been shooting for over 50 years, this is when you don't have your eye close enough to the scope and therefore don't get a full field of view. I've read that it effects accuracy. I was shooting my 7mm WSM and with some loads I got wacked on my glasses. My scope is a 3x9 Bushnell Elite 4200 and at 9x doesn't afford enough eye relief to some of my 7mm WSM loads so I resorted to backing my head back a bit to give me more eye relief. I should have backed off from 9x to 7x but didn't. A month ago, starting with N204 and 154 grain slugs, my starting load of 58.0 grains gave me a 1.0" group which was better than I was getting with a couple of other powders so I thought I was on the start of a good combo. For my next session, I loaded 58.5 to 60 grains in 1/2 grain increments. 58.5 gave me a 2.6" group, 59 grains gave me a .369" group (all touching), 59.5 gave me 1.95" and 60.0 was 1.5" I was dumbfounded at the group variation. Could the "Scope Shadowing" t be the reason I couldn't duplicate the .369" group or even the 1" group? Thanks.
 

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. . . I got wacked on my glasses. . .Could the "Scope Shadowing" be the reason I couldn't duplicate the .369" group. . .
No. Moving your eye straight back from the scope won't change POA/POI. . . but flinching and/or tensing differently WILL.

If you moved your head back, you changed how you were holding the gun, probably differently between every shot. With a round as energetic as 7 WSM, changes in the stiffness of your contact with the rifle (both hands, cheek, shoulder) will absolutely move POI. A <0.5" group would depend on very consistent stiffness/grip/shoulder contact/cheek weld; you probably weren't consistent after getting bit.
 
Parallax might be part of the problem, but at most we're talking about an error of no more than 1/4-3/8" at 100 yards. And even then you won't get any errors if your eye is directly behind the crosshair no matter how far from the scope.

Either you got lucky with the .396" group, 59 grains of powder is considerably more accurate than the other charges, or you're flinching. I'd load up some more at 59 gr and see if you duplicate the accuracy.
 
Many thanks for taking time out to reply. Looks like the next step is to load up some 59 grain loads and see what happens. I will cut scope back to 7x and use a similar target but one I made for 2x7 scopes. Will report back.
 
lowmilage,
Looking at the big picture here what stands out to me is this. Keep in mind I've never loaded for a 7 WSM but have loaded for my high powered 6.5, 7mm, 30, and 338 calibers for a long time. You reported to shot a 1.00", 2.600", .396", 1.95, and 1.500" respectively going in the order from lightest to heaviest load. One group really stands out. That is the .396" obviously. But usually if the powder is close to "working" with your cartridge of choice, bullet weight, and rifle harmonics you should have seen something closer to this example:

1.00, .396, .750, 1.00, 1.25 notice how if you graph these group I put in my example, its linear sort of speaking. Meaning its started at 1.00 when down and started back up with any large dips or spikes. When you have results like you originally shot above there is a huge spike representing the .396" group. I would interpret that to say the .396" group is the exception to the rule rather than "the" load. So me personally, I would question if that powder, bullet weight combo really works in your gun.

Here is an old saying that holds true all day long: One good group an accurate rifle does not make.

Actual realtime example when loading for my 30-06 may years ago. I loaded 49, 49.5, and 50gr of IMR4064 with 150gr Sierra GK bullets. First load of 49gr shot .256" 3 shot group. The 49.5 and 50gr loads were over an inch. But back then I didn't have the experience I do now. So I keep trying to get the 49gr load to shoot again. Never did shot anyhting close to that .256" group with that rifle with 150gr bullets. Shooter and wind can throw shots in as well as out of the group!

So if you go along with this line of thinking in that this powder and bullet weight combo just doesn't agree with the harmonics of your rifle, I wouldn't get too caught up in throwing smal "fixes" at this with worrying about parallax or something like that and trying to duplicate that .396" group. One of the posters above said parallax in this case equates to 1/4"-3/8" of error and I fully agree. Find a powder/bullet combo that when you load it with 3 loads that vary by 1/2gr each and they are all an inch or under.... then you have something to work with.
Now, there is a whole lot more to this and you must look at your whole shooting system if you want to get good consistent small groups, even from a large caliber chambering like a 7 WSM. The reason you probably got whacked with the scope when you backed off from the scope if that in order to see the center of the scope your had to move your face straight back, but that also means you had to raise your face off of the stock. You lost cheek weld. The rifle recoils and instead of you having a good cheek weld and riding the recoil out, the rifle recoiled and your face stayed still and the scope caught your glasses. I would suggest for the duration of you working up a load is to set your scope on 9 power and reset the position of the scope in your rings so that you have a full field of view at 9x and full cheek weld and all. Then when you have the load you want to go hunting with, move your scope to where you have a full field of view at the lower power and shoot your accuracy load all day long to sight in and practice. Will you shoot the really small groups during sightin at lower power... no. But you have already proven this "new" load works. Just sight it in and go hunting.

Good luck,
Steve
 
Steve, I agree with you. I don't like the idea of a great group being displaced by two other crummy groups separated by a half grain of powder on each side. If I get a group that I'd settle on, I like that the groups are pretty good whether a half, or full grain more/less on either side. I think to settle my own curiosity, I will reshoot all my N204 groups again. The crazy thing is, with the Factory Federal 160 grain Bear Claw load, it shot pretty good but then I ran across some available brass and reloaded. Also in the back of my mind is that if N204 proves no good, I'll need another powder (RL17 and IMR4831 weren't accurate either) and I'll pick up some Bear Claws. Thanks.
 
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