sighting confusion [Archive] - Glock Talk

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barefoot
03-24-2011, 15:42
I've been combing this sub-forum for a while and can't really find answers to the following, so I beg your indulgence:

Ranging - this part I find very unclear, perhaps because of the sight picture diagram published on the XS sights web page (see link below), which suggests moving the POA a few degrees down as the range increases to 25 or more yards. In my reasoning, the only way this is possible is if the sight line is designed to be at a shallow downward angle so that it intersects with the parabolic (hyperbolic?) path that the bullet travels. By this same logic, it should intersect again as the range increases further (50-75 yards?), so that you would bring the POA up again to shoot at even longer ranges. Am I getting warm?
(link: http://www.xssights.com/sightimages.html )

barefoot
03-28-2011, 09:29
I figured I'd top this once, in case somebody will come along and understand my insane gibberish .. thx.

bentbiker
03-28-2011, 22:46
I believe the easiest way to look at it is that in general, Glock sights are designed such that the sight line is tangential with the parabolic bullet trajectory at about 25yds, so you only have intersection at one point.

sciolist
04-03-2011, 20:21
The illustration in the XS link is not as clear as it could be. The two Sight Picture sketches on the right show what appears to be the same target at Close Range and Extended Range.

In terms of trajectory, there isn't going to be that much difference between 15 and 25 yards - or let's say, 7 and 30 yards, to account for their "and in" and "and out" qualifiers. Where there will be a great deal of difference is in how much of the target is obscured by the front sight.

If the Close Range target picture applied to 7 yards, the front sight would obscure the entire target at 30 yards. In order to have an effective visual index at the longer range, you'd have to sight the gun in so that the top of the front sight was just below (as opposed to covering) POI. That configuration is known as "center hold".

Handguns for defensive and Practical Shooting use are often sighted in for center hold at 25-ish yards. That allows the shooter to get accurate registration on a smaller target - even if the target appears smaller than the front sight.

At close range (7 yards or so) it's fine to shoot with the front sight (dot, in this case) superimposed over POI. You'll still get good hits that close, even if they are a tad high.

Fast shooting at close range is done mostly from physical index anyway. The critical skill is being able to press the gun out with the bore axis properly aligned on the target, and little or no visual verification. As the range increases (and/or target size decreases) a coarse visual picture becomes necessary, and then at greater range, a more refined picture is needed.

For example, if you were shooting a steel stage with several 18x24 plates at 10 yards, and 6" diameter stop plate at 20 yards, you'd want to be able to refine your sight picture into a 'center hold' just for the stop plate.

bobelk99
04-04-2011, 19:26
Either I or the OP have a misunderstanding of the intent of the Sight Pictures on the XS website.

Ignoring all references to vectors, parabolics, curves or other scientific data, They are suggesting that a close target can be sighted center mass, and you will still be able to see the target.

As the target is moved further away, a sight picture for center mass will likely, and undesirably, obscure the entire target and leave you shooting by guesswork.

In no way are they saying one should aim lower for a more distant target. The assumption is that the gun is sighted for 6 o'clock hold at 25 yards, and at very close range the gun will still hold sufficiently on target.

Any projectile starting dropping the moment is leaves the muzzle if sighted horiziontally to the intended target. The idea is that it crossing that horiziontal line at, say, 12 and 25 yards. You are dead on at 12 and 25, a little low or high at other ranges.

I have no actual comparison data for handguns, but a particular long gun I have hits 2" high at 100 yards, dead on at 200 and 5 low at 300.

Does the concept make sense, or am i the one misunderstanding?

barefoot
04-06-2011, 10:47
Thanks for the discussion, folks - I have to say it's been elevated to a level that requires undivided attention for me to process! (and I'm trying to disprove the old dogs/new tricks dealio)

RimShot
08-07-2013, 00:50
Original link seems to have 404'd...
http://www.xssights.com/sights/pix/24-7-align.gif