Scopes and bullet impact point

HughF

Hi

Maybe one of you guys that spend a lot of time target shooing might be able to explain this one for me. If I change the position of my head on the stock of a rifle does this cause me to have a different bullet impact point each time. I always thought it was the same point provided you could see through the scope without any black rings in the view

Does wearing or not wearing glasses cause a different impact point?

The reason I ask is because when i was shooting a friends rifle recently I noticed that my groups were 1 inch higher than his on the same scope and rifle. It was a good Heym and a good quality S&B scope so I kind of discounted the hardware as being the cause.

Thanks

Sparks

It's more likely to be down to a different head position throwing the rest of your shooting position off, so long as you really have identical sight pictures in both cases.

demonloop

Different pressure being applied to the cheekpiece/stock will also affect bullet impact. Its quite easy to vary the pressure trying to get your head behind a scope or sights for that matter. Variation ain't good. Consistency is.

HughF

I dont think pressure was a factor as the barrel was completely free floated. The stock was a kevlar Mc millian and the action was bedded in Devcon. The rifle was shot off Harris Bi-pod a with a sand bag under the butt.

I am still puzzled as to how the head position might give a different impact point. Is that what paralax is all about and if so would a very good scope like S&B not remedy that at 100M as a matter of course

Sparks

HughF wrote: »

I dont think pressure was a factor as the barrel was completely free floated.

Cheek pressure wouldn't have anything to do with that though - its the pressure of your head on the stock. The point would be that changing that pressure, even in a small way, will throw the whole shot off and you probably wouldn't even notice it change because you're so focussed on aiming and keeping your trigger pull smooth and even.

rrpc

HughF wrote: »

I dont think pressure was a factor as the barrel was completely free floated. The stock was a kevlar Mc millian and the action was bedded in Devcon. The rifle was shot off Harris Bi-pod a with a sand bag under the butt.

I am still puzzled as to how the head position might give a different impact point. Is that what paralax is all about and if so would a very good scope like S&B not remedy that at 100M as a matter of course

The rifle will recoil differently with different cheek pressures. You won't notice it, but you've set your sights according to where the shot goes when you pull the trigger. If you do everything the same for the next shot it will go in the same place. Change something and it will go somewhere else.

All your input through the stock will have an effect on where the shot goes, that's why benchrest shooters have minimal contact with the rifle.

And yes, it's astonishing the different affects different people can have on shot placement on the same rifle. I had two juniors training a week or so ago off the bench and I had to adjust the sights 15 or so clicks vertically as each took turns.

tac foley

Everybody has different eyeballs.

Everybody has an optical centre of focus in a different location on the retina.

Everybody therefore 'sees' the crosshairs in a slightly different location.

However, those points having been made, I'd like to reinforce them.

1. A consistent grip on the gun is vital - both hands working together. A trained marksman holds the gun with both hands for good reason.

2. A consistent pressure of the face on the cheek-piece is vital - this pressure distorts, in a small way, the shape of the eyeball, and THAT also contributes to the 'wandering focal point' within the eyeball.

3. Unless you have been trained, or have trained yourself, the use of the bipod is not a guarantee of pin-point accuracy. Again, the forward pressure on the bipod must be consistent. It is not just there to prop the gun out of the sh*te.

4. Although the bullet has long left the barrel by the time you feel the recoil, the follow-through action at the time of shot-release is a very important part of the shot. Failure to maintain a consistent shot-release and follow-through will make certain sure that your shots are not place on the target with any degree of consistency. It's true that a deer's vital area is lot bigger than the average five-shot shot at any range out to 35-400m, and that you will only take one shot - usually], but the ability to place all shots in a very small area will ensure that the single shot that you DO shoot will be in the right place.

My $0.02.

tac

Jonty

Parrallax error? perhaps

ejg

S&B sets paralax at 200m as far as I know.
So it could be down to paralax at 100m.
I prefer scopes that one can twiddle paralax.
edi

tac foley

Jonty wrote: »

Parrallax error? perhaps

That's the one I missed out.

Well-spotted. ;=)

tac

HughF

Thanks for the comments so far. What would a paralex error at 100M result in. Would it be as much as 1 inch or more and would it not also be from side to side as opposed to up and down?

Tackleberrywho

HughF wrote: »

Thanks for the comments so far. What would a paralex error at 100M result in. Would it be as much as 1 inch or more and would it not also be from side to side as opposed to up and down?

Parallax is an apparent displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. The term is derived from the Greek παράλλαξις (parallaxis), meaning "alteration"

So in short it could be an inch, that is why getting someone else to zero a rifle will never get you pin point accuracy.

It's very apparent if you look at something in a digital camera and what you point it at is not what you see on the screen as you are looking at the objective at an angle to the objective lens

So if you are consistently 1" high, right or what ever, adjust your scope and that is "your" Zero.

ejg

Just hold the rifle steady and move your head left right up and down. If the crosshair moves on the target then the paralax is not adjusted for that particular distance. The ammount of movement can be the ammount of error. Take a scope that can be adjusted with that little third turret or front mounted adjuster, then you should not see a moving crosshair once adjusted correctly. In this case another shooter will/can shoot in the same spot...
at least that's the way I understood it..

edi

Tackleberrywho

ejg wrote: »

Just hold the rifle steady and move your head left right up and down. If the crosshair moves on the target then the paralax is not adjusted for that particular distance. The ammount of movement can be the ammount of error. Take a scope that can be adjusted with that little third turret or front mounted adjuster, then you should not see a moving crosshair once adjusted correctly. In this case another shooter will/can shoot in the same spot...
at least that's the way I understood it..

edi

in other words buy a nightforce NXS

shanmoll308

ejg wrote: »

Just hold the rifle steady and move your head left right up and down. If the crosshair moves on the target then the paralax is not adjusted for that particular distance. The ammount of movement can be the ammount of error. Take a scope that can be adjusted with that little third turret or front mounted adjuster, then you should not see a moving crosshair once adjusted correctly. In this case another shooter will/can shoot in the same spot...
at least that's the way I understood it..

edi

Exactly!