Bore-cite. Fast, accurate, cheap.

The technique works best on long, 30 or smaller caliber barrels. Start by removing the firing pin and steady the barrel in front of a window. Without touching the rifle, look through the barrel and find a distant target, as near dead center of the immage through your barrel as possible; this sight poistion must be held without touching the tool, so find something to hold the rifle steady. Now, you need to adjust the reticle of the scope (or whatever your sight tool is) so the horizone of the crosshairs are perhaps centered an inch bellow the target point (if you were standing at the target) and perfectly in line with the vertical position. Use your knowledge of your bullets trajectory to place the crosshairs on the right horizon point of the target at a given distance (which should never be further than a hundred yards anyway). Generally, this means the crosshairs are "set to strike" an inch or two bellow the barrel targets image because the copper will rise and fall within a variance of an inch; this is acceptable for hunting within 100 yards.

No ammo required.

This will save you a lot of money on ammunition if you aren't a recreational target shooter and you won’t pollute the environment with lead at a range or wherever else you may have centered it. 

Make sure you have excellent vision if you attempt this technique for hunting purposes. 

Take your time and do it right. Check, check and recheck later that you set the cite well; then check again later.