Scope Alignment and Bullet Impact - Help!

[PeteG]

So this weekend i went out and had a bit of range time with my 300wm, shooting sako ammo, the 180gr ArrowheadII.

It was a little low and left at 100m, so i moved the scope a bit to be 1/2" high at 100m, i left the horizontal as it was, as i only wanted to move one thing at a time while we checked out what was happening (and as we were supposed to be out hunting, i was happy at 1/2"left of centre at 100m) and then we moved back to 150m and 200m to see the effect and the bullet path.

This is where it gets a bit confusing for me.

At 150m, the group hit about 2 1/2"right and 3"high of centre, the group was quite tight.
there was a small breeze coming through from the left, but not strong at all and i would've guessed minimal effect on the bullet. the range is in the open, but to the left is pretty thick bush and tall trees so i did not think the wind would cause much drift.

At 200m, the group hit about 3 1/2" right and about 2" high.


The shots were good, nothing indicating a flinch or a bad shot in general, I felt pretty steady and the rest was off the bonnet of the crusier with thick soft blanket rolled up as a rest. only my elbows were resting on the vehicle so no part of the gun was in contact with the vehicle.

The shots in each group were pretty tight at all ranges.

So to all in the know, please help...

and for interests sake, it all came together a bit later on to put some meat in the freezer!

 

[Kano]

A 10 mph breeze at 90 degrees from the trajectory would give you approximately 2.5" to 3" drift at 200 m.

 

[PHOENIX PHIL]

I would also make sure you're scope is leveled properly. If it's rotated, this result can happen.

 

[PeteG]

A 10 mph breeze at 90 degrees from the trajectory would give you approximately 2.5" to 3" drift at 200 m.

Thanks Kano, I didn't think the wind was as much as 10mph, but after a long long evening with spike.t, my senses may have been dulled slightly!!

 

[PeteG]

I would also make sure you're scope is leveled properly. If it's rotated, this result can happen.

Thanks Phil, I will check on that and see how it goes.

 

[lcq]

So this weekend i went out and had a bit of range time with my 300wm, shooting sako ammo, the 180gr ArrowheadII.

It was a little low and left at 100m, so i moved the scope a bit to be 1/2" high at 100m, i left the horizontal as it was, as i only wanted to move one thing at a time while we checked out what was happening (and as we were supposed to be out hunting, i was happy at 1/2"left of centre at 100m) and then we moved back to 150m and 200m to see the effect and the bullet path.

This is where it gets a bit confusing for me.

At 150m, the group hit about 2 1/2"right and 3"high of centre, the group was quite tight.
there was a small breeze coming through from the left, but not strong at all and i would've guessed minimal effect on the bullet. the range is in the open, but to the left is pretty thick bush and tall trees so i did not think the wind would cause much drift.

At 200m, the group hit about 3 1/2" right and about 2" high.


The shots were good, nothing indicating a flinch or a bad shot in general, I felt pretty steady and the rest was off the bonnet of the crusier with thick soft blanket rolled up as a rest. only my elbows were resting on the vehicle so no part of the gun was in contact with the vehicle.

The shots in each group were pretty tight at all ranges.

So to all in the know, please help...

and for interests sake, it all came together a bit later on to put some meat in the freezer!

When you mounted the scope and bore sighted it with the reticle centered how far did you have to crank it? Some scopes have limited windage and elevation so if they are almost limited out then cranking one adjustment will effect both. It is always good practice to align the scope with the reticle as centered as possible. I have a Shepherd and they are notorious for limited adjustments, I had to reverse mounts and shim it. My 30mm leupold has adjustment to burn so it was really easy.

 

[browningbbr]

Did you put pencil marks on your scope to see if it is moving due to recoil? "Creep" in the rings will often account for hard-to-explain movement of bullet impact point. If you find this to be the case, lapping the rings to increase bearing surface will remedy the problem.

 

[PeteG]

When you mounted the scope and bore sighted it with the reticle centered how far did you have to crank it? Some scopes have limited windage and elevation so if they are almost limited out then cranking one adjustment will effect both. It is always good practice to align the scope with the reticle as centered as possible. I have a Shepherd and they are notorious for limited adjustments, I had to reverse mounts and shim it. My 30mm leupold has adjustment to burn so it was really easy.

I cant remember how much i needed to adjust it, its a Leupold VX1 3-12x42.

 

[PeteG]

Did you put pencil marks on your scope to see if it is moving due to recoil? "Creep" in the rings will often account for hard-to-explain movement of bullet impact point. If you find this to be the case, lapping the rings to increase bearing surface will remedy the problem.

I will check the scope for creep, it shoots good groups at each distance so i assumed the scope itself and mountings were ok.

 

[greyfox]

Listen to Phoenix Phil, scope is out of level. I'd bet on it, or you are canting the rifle, just a bit and the further you shoot, the more pronounced the cant.

 

[IronCowboy]

Here's a little diagram I put together a while back - this is depicting a 4MOA hold over (not dialing) with canted reticles, for the case where the shooter holds the scope level and rifle canted and the case where the shooter holds the rifle level and the reticle canted. The hold-over correction represents one of my 30-06 loads fired at 300yrds. The orange dot indicates the aiming point, the green dot with the "X" represents the actual bullet strike.

Canting your scope relative to your bore can do terrible stuff.

 

[spike.t]

Thanks Kano, I didn't think the wind was as much as 10mph, but after a long long evening with spike.t, my senses may have been dulled slightly!!

slanderous statement!!!!

 

[IronCowboy]

I forgot to mention - sure wish I had put it all on the image itself - the scope in my diagram above is 10degrees canted - nothing really huge. I've even had scopes that were professionally mounted that came back over 10 degrees off!

 

[PeteG]

slanderous statement!!!!

Dont make me take pictures for proof next time!!!

 

[PeteG]

Thanks for all the help guys, seems the scope was not leveled perfectly and as i adjusted the scope for a higher point of impact, it caused the shots to drift right.
Definitely no problem with the scope itself and the mounts.
I did not allow enough for the wind either!

More practice i suppose...

 

[spike.t]

Dont make me take pictures for proof next time!!!

oh yeah just remembered the part where we stopped for refreshments on the way back.......... but i do love the way those 750ml water bottles convert into 2 vodka and coke glasses

 

[PHOENIX PHIL]

oh yeah just remembered the part where we stopped for refreshments on the way back.......... but i do love the way those 750ml water bottles convert into 2 vodka and coke glasses

Orange vodka I presume?

 

[spike.t]

Orange vodka I presume?

nope phil the ordinary grey goose as pete couldnt find any orange stuff in ndola, and had to get someone at the airport to buy it for him in the air-side shop , but it went down well

 

[PHOENIX PHIL]

Pete,

I have this kit from Wheeler:

http://www.midwayusa.com/product/816462/wheeler-engineering-scope-mounting-combo-kit-1-and-30mm

It's perhaps a bit over the top, but thus it goes for someone like me who can't be helped in respect to tools and gadgets. The magnets that are included in the kit will help you level the scope.

One magnet goes on top of the top scope turret and the other sits on the feed rails. With the bubble on the feed rail magnet centered, rotate your scope as necessary to center the bubble on the scope magnet. When both bubbles are centered, you're pretty much there. Characterizing your rifle at distance after that, may lead you to just "tweek" the scope rotation. But at hunting distances you're probably good to go from my experience. I mean if you're group a 1/2" to one side or another at 200 yards, is there much point in continuing to chase the problem for a hunting rifle?

This can be a bit of a maddening process. You want the rings on your scope to be snug when you're doing this so that you don't bump the scope and inadvertently rotate it after getting it centered. Trust me, it's easy to do that when the rings are loose. But obviously you want them loose enough that you can still rotate the scope. Also if they're too snug as you try to rotate the scope you'll be rotating the rifle too and you'll rotate the scope in little jumps. And back and forth you'll go until you get to the point of considering throwing the whole operation out the window.

But in the end you'll end up with your scope mounted much better than what you'll typically get from the guys manning the counter at the outdoor shop. They'll "mount" the scope and boresight it for you, but that mounting job is somewhat sloppy.

The kit I put the link to includes bars for ensuring your rings are in alignment. For rings like the Warne's that I use that come together horizontally this isn't necessary. But if you use Leupold rings or the kind that have a top/bottom half and you rotate into place, these bars are very useful for ensuring you've got a nice flush fit at both rings.

It also contains a bar and the compound for lapping your rings. Is lapping your rings necessary? Not likely, but depending on your level of OCD when it comes to mounting a rifle scope, it may make you feel better that you've taken this to another level. But in the end up to 300 yards this is likely not that important.

 

[PHOENIX PHIL]

nope phil the ordinary grey goose as pete couldnt find any orange stuff in ndola, and had to get someone at the airport to buy it for him in the air-side shop , but it went down well

Glad to see you're surving without your favorite there in the bush!