>> Is there anywhere on the net I can go to find out that if a rifle is sighted at 25 yards dead on the bullseye, how far will it shoot before the bullets changes or drops?
That answer will be totally dependant on a large number variables unique to your specific situation, such as:
- The distance you intend to zero at
- Sight height (height difference of the line of sight and the bore)
- Muzzle velocity
- Ballistic coefficient
- Ambient temperature
- Any cant, induced by the shooter or less than perfect alignment of the sights and barrel
- ...among others
Any one of these factors alter where the zero lies given an Initial Intersection of 25 yards. Predicting this requires knowing and measuring a these variable and running the numbers through ballistic software (or calculating by hand.) Even then, the only way to tweak it exactly is to shoot at the actual distance.
Yes, the military uses reduced distances for sighting in, but the formula works because everyone uses the same issued rifle with the same issued ammo.
Even then there are problems. Testing has shown the Army 25 meter zeroing procedure commonly needs to be tweaked when shot on a Known Distance range. This has been confirmed too many times to mention.
The ugly truth is the prescribed 25 meters is of convenience (the Army already had 25 meter ranges) and is a compromise. Soldiers, including the leadership, simply regurgitated this figure as accurate. None of
them bothered to grab a rifle, head out to the range and find out! The Marines, being a bit savvier in regards to basic rifle marksmanship training, have since modified this zero distance.
The only way to accurately confirm a true zero is to actually shoot your rifle with your chosen ammo at the actual desired distance.
What is the ideal zero distance? Unless you have a compelling reason to do otherwise, my general rule of thumb for big game rifles is to zero dead on at 200 yards, or about 2 inches high at 100. We can quibble
about why your specific rifle/sight/ammo works better when zeroed at some other distance, but I'm giving a generic recommendation for any big game rifle shooting any type of suitable ammo (MV 2,000 - 3,000 fps or faster) with any type of sight.
If the only range you have available to you is 25 yards, don't despair! Despite this handicap, you can still carry out an effective field-shooting program. Smallbore gallery targets (A-17, A-36) are shot at 50 feet and a good way to practice basic position shooting. HunterShooter has reduced quarter-sized silhouettes for rimfires, and would allow simulating shots out to 100 yards when placed at 25. There are a number of reduced-range scaled targets for many shooting applications. Brush hunting scenarios can realistically be held within 25-yard distances, and fast moving targets are a challenge at any distance. Reactive steel comes in different sizes as well.
If it is extremely difficult to find a bigger range for even a once-a-year session, my best advice is to start actively shooting and promoting events at the range you have now. Create such a demand for organized shooting in your community that a large percentage of the gun owners and hunters in your area get off their butts and insist a new range gets built.
The only reason you don't have a better range available is because too few people in your area have made too little effort in creating the interest and resources needed to get one built.
Until that changes, how can you confirm an accurate zero on a reduced range, given the variables involved? What I recommend is to buy or load a large lot (several hundred rounds at least) of the chosen hunting
ammunition, find a range that does offer longer distance, wherever that might be, grit your teeth and go spend a day there.
Obtain a satisfactory zero at the actual measured full distance of 200 yards or whatever you decide. Confirm the zero from field shooting positions (Sit, Prone, etc.) with the rifle in the condition it will be
in on a hunt or at a match, i.e., cold barrel.
After confirming, immediately shoot a good 5 round group on a target at a measured 25 yards without
touching the sights. Mark the center of the group and photocopy that target.
You now have short range zero targets customized for your rifle and the desired zero for your ammunition of choice. To confirm your zero, set your photocopy custom target at a measured 25 yards and sight in to the