I shot a Ruger American chambered in 7mm-08 today fairly well at 100 yards. Each 3 shot was perhaps 1.5 MOA, but the 3 shot groups moved around the target about 2-3 inches from 2 o'clock to 10 o'clock to 4 o'clock, etc. with no adjustment to the scope at all. I mounted a low end Nikon scope myself, but am sure the scope is attached very firmly. I'm fairly new to what I hope will be a good attempt at precision target shooting (I am shopping for an upgrade in rifle and scope). What could cause the groups themselves to shift or move about the target? Thanks!
Moving Groups
- Thread starter CZDave527
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armedwalleye
Member
I had a 7mag once that did that. Had the scope mounted by a reputable LGS, but brought it back. They dismounted the scope, reset the mounting screws with removable locktite after verifying the screws were not bottoming out in the holes, reset and torqued everything in the mount to rifle and scope rings, and gave me a fresh box of ammo for my trouble. No problem holding a single group after that.
denton
Member
There are a lot of possibilities....
Mounting a scope should be done with a torque screwdriver. I should know. Before I figured this part out, I mounted a lot of them wrong. I cringe at some of my early work.
Base screws should be tightened to spec, with a drop of blue Locktite. In many cases, if you tighten the screws to spec without Locktite, they will quickly work their way loose.
Make sure the front base screw is not bottoming out against the barrel before the base is secured. If it is bottoming out, you'll find bluing rubbed off at the edges of the base. Grind a bit off the tip of the screw.
If you are using aluminum rings, there is very often a simple problem. About the time the ring mounting screws are feeling snug, the head of the mounting bolt on the other side of the base pulls part way through the aluminum. (Look for recessed heads.) Once that happens, you'll never get good groups until you fix it.
The fix is to remove the mounting bolt entirely, coat the splined head with JB Weld, and hold it in place with gentle tightening. After the epoxy sets, do not exceed the recommended torque. Use blue Locktite on the threads to make sure it doesn't move.
The action screws might be loose.
The scope might be dead.
A malevolent genie may have simply decided to urinate on your day.
Mounting a scope should be done with a torque screwdriver. I should know. Before I figured this part out, I mounted a lot of them wrong. I cringe at some of my early work.
Base screws should be tightened to spec, with a drop of blue Locktite. In many cases, if you tighten the screws to spec without Locktite, they will quickly work their way loose.
Make sure the front base screw is not bottoming out against the barrel before the base is secured. If it is bottoming out, you'll find bluing rubbed off at the edges of the base. Grind a bit off the tip of the screw.
If you are using aluminum rings, there is very often a simple problem. About the time the ring mounting screws are feeling snug, the head of the mounting bolt on the other side of the base pulls part way through the aluminum. (Look for recessed heads.) Once that happens, you'll never get good groups until you fix it.
The fix is to remove the mounting bolt entirely, coat the splined head with JB Weld, and hold it in place with gentle tightening. After the epoxy sets, do not exceed the recommended torque. Use blue Locktite on the threads to make sure it doesn't move.
The action screws might be loose.
The scope might be dead.
A malevolent genie may have simply decided to urinate on your day.
Skylerbone
Member
More likely your inconsistency is due to well, inconsistency. If you were shooting from a rest, did you place the rifle in a supported area ie close to the receiver or rest it on the forearm? A stock that flexes and makes contact can change POI between groups. If the scope mounting were the real culprit, you should not have gotten groups at all, just a lot of random holes in the target. Don't ever JB Weld any part of your rings.
fotheringill
Member
- Joined
- Mar 24, 2014
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- 397
1. Wind, gusting or otherwise.
2. Loose base screws on the rings.
3. Loose screw(s) on the rings.
4. A bad scope.
I would urge you to swap out to another scope with different mounts and see if results change.
As to torque- Either the scope maker or mount maker will NOT give you the specs. I forget which, but a general rule of thumb is 15-18 inch pounds is good. Nobody wants to be responsible for breakage, so to say.
2. Loose base screws on the rings.
3. Loose screw(s) on the rings.
4. A bad scope.
I would urge you to swap out to another scope with different mounts and see if results change.
As to torque- Either the scope maker or mount maker will NOT give you the specs. I forget which, but a general rule of thumb is 15-18 inch pounds is good. Nobody wants to be responsible for breakage, so to say.
If you're shooting off a front bag or rest watch where it's positioned. I have a Savage Axis with the cheap plastic stock and even after stiffening it I can change POI by sliding the front bag back and forth. With a consistant placement I've shot three shot groups as small as .35" and the POI doesn't change group to group
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