SP1 at 50M how many sight clicks ?

JulianY · Post by **JulianY** » Sun Feb 17, 2008 4:56 am

Does any one have a rule of thumb for how many clicks an SP1 needs for changing the sights from 25 m to 50 m.

Yes I know get a free pistol and leave it alone! but that is not an option at this point in time - my dutch license only allows, one gun for the first year :(

Julian

Spencer · Post by **Spencer** » Sun Feb 17, 2008 5:46 am

Julian,

It will depend on the ammunition and where you aim on the target.

When aiming halway down the white (sub-6), while not Pardinis, both my Standard guns are within a few clicks for 25 & 50m when using Winchester Supreme Pistol, but some Eley I tried needed 10 clicks up on elevation.

Spencer

Tycho · Post by **Tycho** » Sun Feb 17, 2008 5:59 am

In my experience, more or less none at all. May vary with lighting conditions etc., but we are shooting quite a lot of 50m here in Switzerland, and I usually don't have to screw around with my sights at all when changing from 50m to 25m (precision target), holding sub six.

Steve Swartz · Post by **Steve Swartz** » Sun Feb 17, 2008 2:33 pm

Inexact rule of thumb:

Some correction needed for center hold. (4-5 clicks)

No correction needed for 6 hold.

Slight correction needed for sub-6 hold. (2-3 clicks)

For many match SPs with match weight/velocity ammo.

Steve Swartz

JulianY · Post by **JulianY** » Mon Feb 18, 2008 1:55 am

Steve Swartz wrote:Inexact rule of thumb:

Some correction needed for center hold. (4-5 clicks)

No correction needed for 6 hold.

Slight correction needed for sub-6 hold. (2-3 clicks)

For many match SPs with match weight/velocity ammo.

Steve Swartz

Steve

Why would there be a difference depending on hold ?

Julian

Steve Swartz · Post by **Steve Swartz** » Mon Feb 18, 2008 12:42 pm

This is actually a trivial issue but it has to do with how high the sight line is above the bore line, and how the angle of the boreline changes with respect to the sight line for different points below the horizon.

The sights are above the barrel. So when aiming the bullet will always have to "climb into" the sight line to the target.

If you aim/hold lower, there is more angle between the axis of the bore and the axis of the sights.

With center hold, the bullet climbs into the 50m target and adjustment will be necessary between 25m-50m.

As you lower your sight line, the bullet will actually have to climb "through" your sight line to hit the center of the target.

Different "sight lines" are used for different distances; the angle between 25 and 50 (for the same aimpoint) will differ between aimpoints used.

As it happens coincidentally, for many gun/ammo combinations the bullet will (effectively) "climb though" the center of the target at the close-in sight line, while also hitting the center of the target at the far-off sight line.

This is only possible (at pistol distances) if the aim point is actually lower than the desired impact point.

[For a long range rifle the bullet can actually be sighted to climb through a close-in sight line, travel above it for a distance, then fall back into the sight line at a far-off point. I believe this is not an issue for the question at hand, because this becomes negligable for pistol distances/ammo.]

Hard to explain without a piece of graph paper . . .

Steve

JulianY · Post by **JulianY** » Mon Feb 18, 2008 2:05 pm

Steve, thanks for that. no need for graph paper i got first read :)

J

jrmcdaniel · Post by **jrmcdaniel** » Mon Feb 18, 2008 2:23 pm

The simple thing to do is just get a big piece of paper and aim at a spot near the top. The pellet will hit a few inches low (at 50M, a click should be 1/8" or so assuming 1/4moa clicks) so if you are 2" low, click up 16 clicks.

Chairgun is an excellent ballistics program for PCs and can be used for free, I think. If not, there are many free ballistics programs. Any, given speed at the muzzle and BC for the pellet will work well for estimating the drop. "Scope height can be anything since all you care about are the extra number of clicks from 25 to 50m) but if you must, set it for about .5" or so for iron sights.

Best,

Joe

Steve Swartz · Post by **Steve Swartz** » Mon Feb 18, 2008 3:31 pm

Actually from an (obsessive-compulsive) engineering standpoint, I believe:

- that for each distance pair (close and far) and
- relative target heights below horizontal from muzzle and
- each gun/ammo combination (critical factors of height of sight line above boreline vs. ballistics)

There will be a "sweet spot" where the aim point will be identical (ie a solution that satisfies the distance pair) for both targets.

Anyhow I'm sure there are probably only a small handful of us who care!

To quote a TT poster of note "They call them 'adjustable sights' for a reason!"

Steve Swartz