ref scope Zero and what makes it move

[pavman]

Not quite as simple as it looks, you have a nice zero on the centre fire 1 inch high at 100 yards and then you miss a sitter, so you check your zero and its off, in my case 2 inch low and 1/2 inch right, I normally group 3 shots in 3/4 inch or better. Fortunately a complete miss I have been musing this fact with Foxing friends and the opinions are varied and diverse. Any ideas and science behind is welcome. I have a top of the range S&B PMII on my Tikka .243 Varmit

Edited September 21, 2010 by pavman

[harv]

Barrel fouling,scope took a knock,mounts loose,mod loose,different ammo batch...your a **** shot and alcoholic poisoning!

[docholiday]

stating the obvious... but guess the scope was bumped, or loose mounts ???

 

mind you could have been to much

 

or perhaps should have gone to spec savers

 

[al4x]

only real answer is something has moved as though only two shots they are close enough to group. Bit of a ****** when you've spent that amount on the setup, are the mounts etc still good and tight, if they are have you done anything different like put a bipod on it etc

[pavman]

only real answer is something has moved as though only two shots they are close enough to group. Bit of a ****** when you've spent that amount on the setup, are the mounts etc still good and tight, if they are have you done anything different like put a bipod on it etc

 

 

nope checked mounts and mod was tight etc, nothing new nothing changed, and all seems ok now as i have checked it again it bothers me i cant think what I have done

[garyb]

There are so many factors that can change the POI..

 

I've seen rifles that group fine, and then like a shotgun just by fitting a bipod!

 

You will only know something is up when you miss one... as you have found out...!

[al4x]

you've adjusted zero i take it rather than it returning to zero, If everything is tight and you have done nothing then you either have to hope it got knocked or you may have to send the scope back to be checked if it decides to do it again. Problem is its going to knock your confidence with the gun

[the running man]

you've adjusted zero i take it rather than it returning to zero, If everything is tight and you have done nothing then you either have to hope it got knocked or you may have to send the scope back to be checked if it decides to do it again. Problem is its going to knock your confidence with the gun

yes,al4x is right,get back down the range,sort it out,nothin worse than being very unhappy with a gun.

[GRamsay]

Temperature can make a difference in shot placement as it affects your scope

[pavman]

Temperature can make a difference in shot placement as it affects your scope

 

 

science requested plz

[pigglet]

I'm sure I remember reading an article about PMII's being badly effected by temperature deviation and that a number of them had been returned to S&B for that reason??

Can't remember the circumstances or temperature ranges though.

[dunganick]

Most likely answer is the gun has taken a knock. Even though the scope/mounts/stock are tight they will still move if knocked hard enough (you might be surprised how easily this happens). A change in humidity can also effect pressure on the barrel from the stock if you don't have a floated barrel.

 

I would re zero and carry on. It happens to even the most reliable, sturdy gun.

[garyb]

science requested plz

 

 

Velocity is affected by temperature

 

Not sure about scopes

[kent]

As stated many things, but the last place i would look would be the scope itself S+Bender are very good at holding zero generally. Temprature effecting the ammo (hot temps can increase presure low temp the reverse) something messing up the free float like a bit of twig etc, loose action screws, loose mounts, natural wood stocks can move with temprature and humidity, different hold from the shooter, clean barrel / dirty barrel on and on. Fact is it's easier to eliminate these things from the off than it is to find which is responsible. If your using factory ammo i think this most likely the cause

 

To explain, avoid walnut stocks unless pillar bedded and sytheticaly bed laminate and composite. Check the action screws, free float etc before use. The most important thing of all is knowing the gun and ammo and the only real way of doing this is a shooters log developed over time. Things like when the acuraccy changes between cleans, how your ammo performs through differing tempratures etc.

[Paddy Galore!]

Velocity is affected by temperature

 

Not sure about scopes

density of the air can affect trajectory, extremes of temp can make the body of the scope expand or contract.

clutching at straws here but has one of the turret caps had a knock or been depressed, i had a cheaper make scope once that when i zeroed the rifle i took the caps off, set up all hunky dory, put the caps back on and it pressed on the top of the turret, knocking the zero off by a few inches.

[pavman]

went out last nite and decided I would do a quick re check the zero (set inch high 100) no problems inch group (50 p coin)so just to rub it in Charlie never showed up

 

The Rifle is as stated a .243 Tikka Varmit synthetic stock floating barrel 56 mm S&B PM II with 34mm tube and mounts. Everything checks out is tight and correct and now re zeroed and re checked. I take care of my kit so it drives me nuts when i miss and find no apparent reason

[al4x]

fingers crossed for you, sadly Fister is usually right but first time I've heard that

[Blackbart]

Just how much of a "knock" do people think it would take to shift zero ?

 

The reason i ask is i seen a vid once for leupold scopes and the guy shot a target about 300 yards away then got hold of the rifle by the barrel and threw it as far as he could,walked after it,picked it up and returned to his original place lay down and hit the target again 300 yards away !

 

I would think a high end scope mounted right would have to be seriously abused to change its zero,so i would think ammo,barrel foul or something contacting barrel to stock.

 

Had something similar and turned out to be a slither of wood between barrel and stock that had become wedged in there somehow.

[dunganick]

My Howa used to be bad for it, i used to use some bushnell mounts with shims (much like optilocks) but made to a price. I used to carry the gun on the back seat and if i had to brake hard and the gun slid off the seat into the footwell i could almost guarantee that the zero would of moved.

 

I have since moved to a rail system where i have shimed the bases instead of using adjustable mounts and the gun has been great since (and carry the gun in the footwell).

 

But i have seen it loads with my old mans guns (over the last 10 years), they take a knock and its just enough to make the stock slightly shift or scope/mounts move a tad. And he is running swaro's with optilocks on Sako's so none of this budget kit that i use.

 

Dont worry about it unless it keeps moving.

[GRamsay]

density of the air can affect trajectory, extremes of temp can make the body of the scope expand or contract.

clutching at straws here but has one of the turret caps had a knock or been depressed, i had a cheaper make scope once that when i zeroed the rifle i took the caps off, set up all hunky dory, put the caps back on and it pressed on the top of the turret, knocking the zero off by a few inches.

Expansion,contraction-affects your reticule,hence the misplaced shots