Taking an elderly and sometimes rather battered old Enfield that you have just bought onto the firing point and expecting to hit much with it straight away is not a good idea, and is totally contrary to the rules (just about everywhere).
You should first ALWAYS have the rifle checked by someone (other than whoever sold it to you) who knows Enfields well enough to be able to check that it is safe to fire.
Then you need to find out how well it shoots and correct any errors in the setting of the sights and possibly the overall setup of the rifle.
For most shooters they will be zeroing their rifle on the normal range so here are the basic rules.
1. Always boresight the rifle first to make sure that your shots will at least hit the screen. If possible, make use of the Zero Range at Bisley.
2. Zeroing should always be done at 100 yards (to minimise the effect of crosswind) with the backsight set at 200, you adjust the foresight until your mean point of impact (MPI) is roughly 3 inches above the point of aim (POA).
3. Always move the foresight blade towards/into the error. If the MPI is high then fit a higher blade, if it is low then fit a lower blade. If it is to the left then move the blade to the left, if to the right then move the blade to the right.
4. Foresight blades vary in size by 0.015 inches, -0.030 / -0.015 / 00 / +0.015 / +0.030 / +0.045 / +0.060 / +0.075 / +0.090.
5. Blades are always marked to show what size they are, the plus sign is not used in the marking but the minus is.
6. Sight blades should always be fitted from the left side of the rifle and tapped out from the right.
7. At 100 yards, each step in the height of the foresight blade will raise or lower the MPI by approx 2 ¾ inches with a No:1 Rifle, 2 inches with a No:4 Rifle, and 2 ½ inches with a No:5 Rifle.
8. All of the blades are the same height; it is the thickness of the base that varies.
9. For lateral adjustment the best way is to use the correct cramp for the rifle. One complete turn of the cramp on the No:1 Rifle will move the MPI approximately 8 inches to the left or right, or on the No:4 Rifle 5 inches, and on the No:5 Rifle 6 inches. (The variation is caused by the difference in the Sight Radius IE; the distance between the front and back sight, of the different rifles.)
10. If no cramp is available you can adjust the lateral position of the blade by tapping the base with a punch and hammer (once you have loosened the screw if there is one), one blades width has roughly the same effect as one turn of the cramp.
11. To fine-tune your rifle, start with the backsight wound all the way down and then count the clicks needed to bring your MPI to your POA at each range. (4 clicks = 1 Minute = 1 inch at 100yds)
For further information, pictures, and for those who like maths and equations, check out the page The Zeroing of Rifles (according to the REME) in the Information section of this website.
If you are lucky enough to be able to visit the National Shooting Centre at Bisley then your next port of call should be the Range Office, where you should ask for a Zero target for a 303 and they will give you a card that looks like this:
And the Zero Range can be found here at 2:
There will be a separate article on the use of the Bisley zero range added soon.