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  #1  
Old 01-09-2013, 08:53 AM
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Dead on at 25 - Good at 100


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First let me say hello to all. First time user here.

I have found over the years that this works pretty good for me, so I use it as a rule of thumb for most rifle sighting. Use a laser bore sighter and for you short range area guys, sight your gun in to dead on at 25 yds. using 3 to 5 shot groups. The impact at 100 yds will be about -.100" with a 165 gr. bullet. The difference from 25 to 100 yds is so minimal you don't need to worry about it.
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Last edited by GeezerGuy; 01-09-2013 at 08:56 AM.
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  #2  
Old 01-09-2013, 09:08 AM
The Troll Whisperer (Moderator)
 
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been using the 25 yd sight-in rule for over 60 years with all centerfire rifles and find it to be very effective.
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  #3  
Old 01-09-2013, 09:19 AM
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Welcome to the Shooter's Forum and thanks for the first post.

Guess it depends on the rifle, more so on how high the scope is over the bore centerline. I've had them vary from being right on at 100 to being 2-3 inches high. Probably would be good enough for big game hunting but prefer auctually shooting the rifle at ranges i expect in the field.
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  #4  
Old 01-09-2013, 11:45 AM
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It definetly will not work on high mounted scope. It comes somewhat close on scopes mounted at 1.5"
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  #5  
Old 01-09-2013, 12:35 PM
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Welcome to Shooters Forum, GeezerGuy.

Jack O'Connor was a very vocal proponent of this sight-in method. With his pet 270 Winchester rifle and a scope mounted 1.5" high, which is a typical height with most scopes, 130gr bullets that are dead on at 25 yards would be about 3" high at 100 yards and back to zero again out around 225 yards.

With slower guns, and open sights, the bullet will not strike as high at 100 yards. With high-mounted scopes, the bullet will tend to hit 4-5" high at 100 yards, maybe more, when zeroed at 25.

Regardless of how you sight in, it's definitely going to be important to SHOOT at longer distances, so you know for sure where you will hit way out there.
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Old 01-09-2013, 12:47 PM
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Thanks guys, Your input is good. I agree that all rifles and ammo shoot different. It's just a place to start from for some of those who have a short sighting range. It is necessary to resight for the range needed when you have the didtance to do it.
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Old 01-11-2013, 08:13 AM
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With a scope its 25 yards dead on for 1.5" high at 100...

with iron sights its 12.5 yards and dead on at 150...

All this is fine, but its only intended to get you on the paper, you always need to shoot at 100 and check out the zero, barrel harmonics etc. etc, come into play..

I just sight my rifles in 2 or 3 inches high at 100, depending on caliber and hunting conditions and the game to be hunted...I always check my sights at 100, 200 and 300...for instance a .270 sighted in 3" high at 100 is 4 inches high at 200, on at 275. a few inches low at 300 and a foot low at 400...Same with an 06...but you have to check them out as they all will show some difference.
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Old 01-12-2013, 04:17 AM
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Your tolerance for group placement on the target will have to be much tighter than if you are shooting out to 100 + yards though. What I mean about that is, a lot of times, when we shoot at 100 yards, if I am 1" right or left, it isn't that big of a deal BUT if you sight in that way at 25 yards, and that is acceptable to you there, you could very well miss the target completely out to 100 yards.

I can do the math but will leave that lay for now, suffice it to say that one would need to tighten up their tolerances of what is acceptable group placement. Even a half inch @ 25, left or right is a big deal @ 100!

Food for thought.
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  #9  
Old 01-12-2013, 09:45 PM
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That works for some cartridges, in certain bullet weights, and barrels. The 25yd sight in for 100yd shots isn't always the norm nor average.
Depending on your scope.....and if you have a smartphone........Strelok is a decent (free) ballistic calculator for any range and plenty of scopes.
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  #10  
Old 01-12-2013, 11:36 PM
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IME this method gets you close, but that's it. I prefer to KNOW what my sight setting is at 100 etc., rather thsan assume.
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  #11  
Old 01-13-2013, 07:07 AM
The Troll Whisperer (Moderator)
 
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To put this in a nutshell - sight-in dead center at 25 yds, then check for POI at 100 and further ranges as desired. Do not rely on 25 yd being the Holy Grail for all distances.

How's that! (Boy, sometimes I wonder! )
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  #12  
Old 01-18-2013, 06:11 AM
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Welcome Geezer. I've been using that method for a long time myself and it has yet to fail in any rifle I have ever tried it with. I always double check and fine tune at 100 just to be sure but this method has saved me a lot of bullets along the way. I guess the scopes on the rifles I use aren't mounted high enough to be the exception rather than the rule.
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  #13  
Old 01-18-2013, 06:21 AM
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Geezer, it's a great rule to know if only in case you drop your rifle or otherwise bang the scope out of alignment during a hunting trip, especially if you don't have access to an area where you can sight in at 100 yards. If you use this method enough times and go through the steps to confirm that it works at 100 you will have confidence in its validity. If ever forced to sight in at 25 during an "emergency" situation I would have confidence in my rifle and this "trick" because I have done it so many times without fail. I have never yet hunted by sighting in at 25 without confirming at 100 but I would do it based on my experience if my choice was that or quit hunting if I were out of state or something like that.

It's a good practical way to save money on ammo when sighting in and it's a great "trick" to have in your back pocket on the off chance you ever need to use it in an unusual circumstance.
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  #14  
Old 01-18-2013, 10:45 AM
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…And in many exterior ballistics programs, you are able to enter your sight height, your bullet muzzle velocity and bullet ballistic coefficient and set the sights range on 100 or 200 or however many yards you want, and let it calculate bullet drop off the line of sight. Where that's zero before getting to the target is the range at which the bullet crosses the sight line arcing upward on its way to the target. It is the distance you would use for the short target, ideally. If you zero at 100 yards, this distance can be a little long. For the .308 175 grain MatchKing at 2640 fps MV, zeroed at 100 yards, it is about 56 yards at sea level for the short range target (though you will only be about 1/2 inch low at 25 yards). However, if you are following Jeff Cooper's approach to zero at 200 yard, which allows the bullet to strike a couple of inches high at 100 yards, then the sight angle is greater and the short range target should be at about 27 yards for that cartridge. If I zero at 270 yards, so the bullet impacts 4" high at 100, then the short target is ideally at just 20 yards.

A free calculator that will let you do this is here. Set the range increment to 1 yard. The yards are the left most column. The second column is the drop off the sight line, so it should be zero twice, once where your short range target goes and once again at the target range.
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