PH5C sight - how to use it properly?

I have a PH5C on an old No.4 and i am takign to to the range this week - it's zeroed at 100 yards for an "i" sight picture on a 6 inch black.

My friend just informed me that the 300 yard range willbe open and not the 100 this week. i have never shot at 300 yards before with iron sights, so quite aside from the "will I see the damn target" question. I'm wondering how to adjust elevation correctly. How many clicks / lines should it go up for 300 vs 100 yards?

I am using HXP 303 ammunition so standard 303.

A quick search indicates drop at 300 would be about 15 inches - approximately 5 minutes of angle. With your 100 yard zero, the sight should be elevated 5 minutes. Study the Vernier scale. You will be able to change the setting exactly that amount. Your sight probably has quarter minute clicks. 4 clicks moves the point of impact one minute, so you might need to come up 20 clicks. Learning to read the Verner scale is more effective than counting clicks. The plate can be shifted and reset once you have your zero.

You didn't mention what eyepiece you had on the PH5C but can we assume it's a 6 position eyepiece? If so you want to adjust it to the smallest hole possible without dimming your sight picture.

Yes, that will sharpen the image of the front sight.

Be careful because the early PH5C sights were made with half minute clicks. From the mid 1960's they were made in quarter minute clicks. Hence the need to be able to read a vernier scale - see instructions in the attached picture. A quick way to find out is to count the number of clicks when moving the sight from the 200 yard setting and 300 yards (the elevation plates are engraved on the right of the vernier with range settings starting at 200 yards and going up to 1200 yards - the line between 200 and 400 is 300 yards). If you have half minute clicks it will take six clicks to move the 3 minutes needed between 200 and 300 yards. The attached instructions are for quarter minute clicks.

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Originally Posted by newcastle

How many clicks / lines should it go up for 300 vs 100 yards?

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From 200 to 300 you need to come up 3 1/2 MoA (100 and 200 are too close in MoA to worry about)
With a PH5c in half minute clicks this will be 7 clicks on the sight. If the PH5c is a later 1/4 MoA this will be 14 clicks.

If you're unsure whether the PH5c is calibrated in 1/2 or 1/4 MoA then look at the vernier and count how many clicks it takes you to move it 5 MoA, this will be 10 clicks for a 1/2 MoA sight and 20 for a 1/4 MoA.

PM your email address and I can send you a chart with everything you need to know about elevations for .303.

Edited to add: I see Nigel beat me to it!