LF info on Central No. 4 aperture sights

stevebc

stevebc

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... specifically, how to read them. I inherited one from my late father, and it shows a scale on either side of the elevation vernier. I've been using it out to 375 yds shooting somewhat uphill, but need to take it to much longer ranges. I realize I should adjust it upwards, but if anyone has any info on how to use these properly, it would sure be appreciated. To me, it looks as though it tops out at around 1200 yds? metres?
My thanks in advance... :redface:

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OK, you read it just like a vernier, forget about the other scale. You have 19 minutes on the sight now. I try to zero my elevation scale ( 2 screw that you see) at 5 minutes for 300 yards.
What you need to know first off is if your sight ar 1/4 or 1/3 clicks, either 4 clicks will move the sight 1 MOA or 3 clicks will move it 1 MOA.
Next you need to know the approx come ups for the bullet you are shooting.
With 147 gr 7.62 Nato rounds (also close for 155's and 80 gr bullets in a .223)
These come ups are form a known zero for your rifle.
300-500 come up 6 1/2 minutes.
300-600 come up 10 1/2 minutes
300-800 come up 20 1/2 minutes
300-900 come up 26 1/2 minutes
300-1000 come up 34 minutes.

Remember these are approx values and much depends on bullet weight, sight radius, barrel length, your load velocity, etc.
 
The actual change in point of impact, relative to the change in minutes on the sight, will also depend on the distance between front and rear sights. The shorter the barrel, the greater the shift will be.
As Maynard suggested, forget about the distance scale, learn to read the Vernier scale, and your come ups in minutes.
Central sights are excellent. They are simple, dependable, and easy to maintain.
Incidentally, bases can be obtained so that they may be used on a variety of rifles. The sight is intended to be removed when not in use, and will re-attach without shift in zero.
 
I have to head off to work soon, so I'll print the replies and take the sight with me, so I can ponder this over coffee/lunch. Did I mention I'm a total noob at this? :)
btw, each click is 1/4 MOA. I'll post sight radius, twist rate, and grains later tonight. Rifle is a Grunig in 7.62X51.
Thanks guys, this is all new to me. Any additional comments/advice are most welcome!
 
Stevebc, once you have your elevations for each distance that you are going to shoot make sure you write it down along with the load you are using. Keep good records. Your elevations will change depending on the load you are using.
When I shoot 155gr sierra or Hornady Amax at 1000yds there is a 1 minute difference in elevation, but when I load with Lapua's there is a 7 minute difference.

You should also check your windage to make sure what values they are. I own two central sight. The one with the diopter has 1/2 elevation and 1/3 windage. The other sight has 1/3 elevation and 1/3 windage.
 
Ok, I think I'm understanding this, but I'm sure I'll have more questions down the line.
I checked a few things out, and I have a 35 1/2" sight radius,a 29" barrel, with a 13 3/8" right twist. I've been using NATO rounds for practice, and once I get used to things, will eventually start rolling my own.
I have 100rds of stuff my Dad loaded: 155g Sierra Match Kings with 46g Varget, Federal 210M primers in Imperial .308 Win brass. I know this by a) looking at the stuff, and b) I have some of his old range/loading notes :)
I can't wait for Spring so I can get out to the range again. I just wish it was flat,and went out beyond 375yds. Still, it's close by and cheap!

Jose, thanks for the advice. I tend to be a bit sloppy about record keeping, but in this I will be meticulous. Thats a bit odd (to me) about having different adjustments on the same Central sight. I've been assuming that the windage would be the same as the elevation, but I'll see what I get with it next time out.

This is like learning a new language, except that I really enjoy the lessons!
 
Study the way the clicks and the Verniers relate. You will be able to determine whether you are dealing with 1/4, 1/3 or 1/2 minute clicks. The load you describe is a very conventional and successful combination. Velocity will be close to 2950 fps.
 
Jose,
Wow 7 minutes difference between 155 SMK's and 155 Lapua? Most shooter,myself included are only finding about 2 MOA difference at 1000 yards.
Stevebc,
Wind your windage to read "0" on the scale. Then turn your knob 20 clicks, if your sight is 1/4 minute you should now have on 5 minutes of wind.
 
Maynard,
7minutes difference @ 1000yds is right. My first two shots went over the top of the target. There was another fellow shooter he had the same results as me. This was a few years ago at the St Bruno Range. Too bad it's closed now.
 
I rechecked- 1/3 moa clicks on both elevation and windage. Note to self: never assume... thanks guys.
 
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