Resetting my scope - any tips?

[Yorric]

Neutron
Go back to square one basics, you appear to have confused yourself by your actions & assumptions! - Forget your previous trials & put aside your pre-conceptions.
Others have given you some good pointers - Here is my two pennyworth. (assuming your scope is not defective)

1. Check your action is properly secured in the stock & torqued down.
2. Check that the scope bases are securely fixed onto the receiver.
3. Reset the scope crosshairs square to the vertical when the rifle is set level. (double check this two or more ways - spirit level, look at the crosshairs from behind - normal way when in the aim looking at a vertical plumb line etc - look at the rifle from the front end, you can see the crosshairs & the line of the barrel & this shows cant errors quite well, - mount your rifle aiming at a vertical line with your eyes shut then open the eyes)
---- If all these methods look right you will be near enough set up.
-- Note - As you tighten the scope rings you are more than likely to twist the scope barrel in the rings canting it - so re-check it after setting & finally torquing it up.
4. Pick one bullet weight and loading & on a still day with no wind, zero the rifle at short range (just to get on target) then fine zero at longer range - eg 200 yards. - Your group there should be even both vertically & horizontally. (If it isn't - you're probably not holding the rifle consistently). Next check your zero at 100 yards - you should have a smaller, symetrical group a bit higher on the target with no sideways error.

At that stage you should have a setup that you can rely on & you know where it shoots at normal stalking ranges so then you can go stalking!

If you want to shoot different weight bullets go ahead & see where they shoot - You may be lucky & get group that requires no re-zeroing - but you probably won't!
Your rifle will react to the different bullets as Bewsher indicated (barrel whip et) & the different recoil may be making your pattern move diagonally too --- You have to be sure your hold and firing position is consistent/solid & zero for your chosen bullet weight.

Ian

 

[bewsher500]

Ok - so I reasoned that one out wrongly and picked the wrong example of the two I had to give you. Mea culpa.

If I said that I'd also shot the same round at two different distances and that the longer distance produced a downward and leftward shift in POI, I think you'd agree that that was a canting error?

I adjusted the scope last night and got it a bit straighter I think. Then the rifle fell over from where it was standing and I did it all again...

Anyway, it's probably not perfect, but it is an improvement I think.

As I hinted above, one of the other problems I was having at the range on Saturday is that the shift between the 100yd and 200yd line was turning a good central chest shot into a low gut shot. I was getting a both drop - more than I'd expect - and horizontal shift at the longer distance, so I wasn't happy - I certainly won't be pointing the rifle at a deer until I have it sorted, or at least, re-zeroed and much improved.

It is possible I suppose..just unlikely
my concern here is that to see the significant effects you are describing needs
a) a cant of 30+ degrees
or
b) significant range...like 400-1000yds

it should not display itself at the change of range between 100 and 200yds
your shots at 100 would be off the mark already by a factor of maybe 1/2-1" at worst
the shots at 200 would be marginally worse like maybe 1-1.5"

that's not turning a firm chest hit into a gut hit

Canting Effect on Point of Impact within AccurateShooter.com

http://www.riflescopelevel.com/cant_errors.html

 

[JMS906]

I am not sure that canted crosshair will walk your POI left-right if you are not altering the elevation turret.
If you are conciously canting the rifle to align with the target frame,you are probably doing so with all of your loads.
The reference point of the scope is the centre of crosshair.

I concur. So long as he holds the rifle so that the reticle is vertical each time he fires, it will make no difference that the scope may be misaligned with the vertical axis of the stock. Secondly, if you have three different loads where the only difference is the powder charge and hence velocity, you can expect the point of impact to move vertically and laterally - not simply vertically. What you can't know, without testing, is know how far and in exactly which direction it will move. Even in still air, a bullet from right twist barrel will move in one direction (relative to the bore's axis) and a bullet from a left twist barrel will move in the opposite direction. If there is a side wind, the effect become more pronounced and more apparent over longer distances (and we are not talking 3-400 yards here).

To the OP, what was the velocity shift in your three loads?

-JMS

 

[neutron619]

To the OP, what was the velocity shift in your three loads?

About 1100fps: 110gr round @ 3250 fps, 150gr round @ 2820fps; 220gr round at c. 2150fps.

All figures approximate - no chrony on Sunday so couldn't get accurate numbers if I'd wanted to. (Now I wish I had.)

In case anyone's about to suggest it, this is a .308 and the 220gr round IS stable. Just drops a bit further than most!

Just to emphasise:

The thing I was most concerned about was the fact that my usual, well tested 150gr round seemed to be dropping 6-7" at 200 yards, rather than the 3-4" it should when working correctly. I'm satisfied the load is good - recoil, the feel of it, etc. were all as expected. The trajectory was not. Unfortunately, that means I've now lost the confidence I had in it.

I will do as Yorric says and get the scope set up as well as I can. Then I'll take it to the range next month and zero it at both distances as advised. Hopefully the problem will either clear up, or, with some more careful testing, I'll be able to work out what's happening and adjust to it.

Many thanks to you all for your help.

 

[Cyres]

If you are getting worried I suggest this. Firstly you will need to purchase a scope level, many makes, Sportsmatch, B square and alike and you will need to fit it. Lots advertised in air rifle mags, essential equipement for Air rifle FT work.

I put my actions in a work mate, fit bottom halfs of rings and align with a spirit level, I also have a sheet of plate glass which I put across the rings, I would be suprised if its flat/touching all parts of the rings, you might have to swap/turn arround the rings to get the best level. Also I hanve a plumb line down the garden, place scope in bottom halves and align plumb line to vertical scope reticule. Now also have a look at your bubble level, and note the postion it is in when the action is level it might not read level but it does not mattter. Attach top rings tighten screws in diaganal fashion periodically checking that the reticule stays vertical.

When shooting always ensure the bubble in the level is in the same position when you shoot then you know its all aligned correctly.

Also note that the vertical reticule can be out by up to 5% so you may never have a 90 degree between horizontal/vertical.

Alternativly if you are a good shot you can use the shoot the box method which will indicate miss aligned scope, but never tried it myself.

D