Need help zeroing for meters.

Status
Not open for further replies.

EvilGenius

Member
Joined
Mar 15, 2010
Messages
402
Location
Texas
Hey guys I need help zeroing the diopter iron sights on my PTR91 for ranges in yards.

I understand the process of zeroing sights in general. The problem I am having here is that most of the ballistics data I can find for .308 (specifically HSM 168gr BTHPM) is all in yards. The 0-100, 200, 300 & 400 settings on the rear sight on my rifle are for yards. So while I could zero any one of those for yards. It'll throw off all the other distances.

I don't expect hunting accuracy from the irons on this rifle and I think the 300 & 400 meter settings are a bit optimistic, but I'd like to at least have the 200m setting close.

I can find tables that will tell me the distances in meters, but 100 meters is the shortest distance listed I can find and this rifle has not been zeroed before and I know the sights are off. I need to get it close on paper at 25yds first before taking it to a longer range.
 
Last edited:
are you trying to convert meters to yards? Just enter the math you want the answer to in your search engine (google or bing) ex; "25m = yards" this gave me an instant answer of 27.3403325 yards.

Or got to wolframalpha.com . this site will calculate anything you'll ever want to know.
 
Tape off 200 meters and set up a target. Adjust your sights until you are zeroed. Likewise at any other range you are interested in.
 
are you trying to convert meters to yards? Just enter the math you want the answer to in your search engine (google or bing) ex; "25m = yards" this gave me an instant answer of 27.3403325 yards.

Or got to wolframalpha.com . this site will calculate anything you'll ever want to know.
Yeah I figured as much.

I don't imagine the bullet drop will be much different over a 2yd distance difference.

Where I get hung up is if I go for a 200yd zero. It should be about 1.25"-1.50" low at 25yds.

But then If I take it out to 200yds, I assume that the setting for 200meters will put me off as 200yds and 200 meters are much further from each other.
 
Tape off 200 meters and set up a target. Adjust your sights until you are zeroed. Likewise at any other range you are interested in.
There are some ranges around here (north Texas) that go out that far, but unfortunately none of them will let you shot at those distances unless I can prove it's accurate on the 25yd range first. Getting it close on paper at 25yds isn't a big deal, but with the differents between yards and meters could still put put me off target at those ranges.
 
200 yards equals 182 meters, or a difference of 64 feet. That's less than the average distance between two utility poles. Do you really think a 308 bullet is going to drop much in 64 feet? Even at 400 yards, which equals 365 meters, you'd be looking at a difference of only 111 feet. (Of course, at that distance, the bullet is already starting to drop faster so, yeah, you'd see a difference.)

But I think you're over analyzing.

Edit: By the way, the English measurements are actually closer the muzzle than the metric measurements, so, if anything, point of impact is going to be higher than expected. In other words, if you set your 200 meter sight to 200 yards, you're only shooting to 182 meters, which means you should be hitting either high or spot on, certainly not low.
 
Last edited:
Those sights are probably designed for 147 gr ball, so the 168 gr trajectory won't exactly correspond to each range setting.

The Hornady calculator linked above says 0.9" low at 25 yd for 100 m zero and 0.3" low at 25 yd for 200 m zero, based on a 2" sight height, G7 BC of .222 under Metro conditions and a muzzle velocity of 2525 ft/s. However, at these ranges the differences are small and the same also applies to generic 147 gr ball.
 
one meter=39 inches. add three inches to every yard and you have the range in meters., eastbank.
 
200 yards equals 182 meters, or a difference of 64 feet. That's less than the average distance between two utility poles. Do you really think a 308 bullet is going to drop much in 64 feet? Even at 400 yards, which equals 365 meters, you'd be looking at a difference of only 111 feet. (Of course, at that distance, the bullet is already starting to drop faster so, yeah, you'd see a difference.)

But I think you're over analyzing.

Edit: By the way, the English measurements are actually closer the muzzle than the metric measurements, so, if anything, point of impact is going to be higher than expected. In other words, if you set your 200 meter sight to 200 yards, you're only shooting to 182 meters, which means you should be hitting either high or spot on, certainly not low.

Very good points.

I probably am over analyzing it.
 
Those sights are probably designed for 147 gr ball, so the 168 gr trajectory won't exactly correspond to each range setting.

Also a good point. I won a bunch of reloaded 147gr at my last 3 gun match, so I'll probably use that even if the overall groups probably wont be as tight as the match ammo.
 
Since we're talking irons, why not just zero 3" high at 100 whatever. That should give you a solid point blank zero to just shy of 300. You'll definitely be on paper - no problem there.

Edit: with that zero, your 300 holdover is 6", and your 400 holdover is 21". Those are 147gr #s.
 
Last edited:
When a young lad in the Army in Germany, I quickly learned the best way to get used to the metric system was to learn it and quit trying to convert to the English system or vice-versa.

Drink two large glasses of beer. If it's an honest gasthaus, that is one liter. Repeat until you have it down pat, even in your sleep

Walk/run 1,000 meters, that's one kilometer. You will learn it quickly.

Pick up kilograms in successively grater amounts until you learn to look at something and estimate accurately it's weight. 1,000 kilograms equal one ton.

I can still see a poor guy walking around with a slide rule trying to do English to Metric conversions. I don't think he ever learned the metric system.
 
When a young lad in the Army in Germany, I quickly learned the best way to get used to the metric system was to learn it and quit trying to convert to the English system or vice-versa.

Drink two large glasses of beer. If it's an honest gasthaus, that is one liter. Repeat until you have it down pat, even in your sleep

Walk/run 1,000 meters, that's one kilometer. You will learn it quickly.

Pick up kilograms in successively grater amounts until you learn to look at something and estimate accurately it's weight. 1,000 kilograms equal one ton.

I can still see a poor guy walking around with a slide rule trying to do English to Metric conversions. I don't think he ever learned the metric system.
Hah!

I work for airbus helicopters, so I get to enjoy the constant bounce between metric and standard.

Metric is so much easier... until I get into a car. Then it's just wrong.

I have no problem with learing ballistics in metric and shooting that way is all of the ranges here are in yards.
 
If you're two inches high at 100 yards, you'll be about dead on at 200 and roughly six inches low at 300. With that set-up, for anything inside of 250 yards, just point it and pull; hell ain't half-full. :)
 
A meter is 1.0833 yards. Difference is negligible until you hit 400 meters.
100 meters = 108 yards
200 meters = 216 yards
300 meters = 325 yards
400 meters = 433 yards

As far as the metric system versus Imperial, a lot of things are just a matter of convenience. However, when precision is needed, Imperial is superior. Everything from linear measurement to weight and temperature, the increments of Imperial are more accurate. I have this conversation quite often with one of our engineers who seems to favor the metric system.
 
As far as the metric system versus Imperial, a lot of things are just a matter of convenience. However, when precision is needed, Imperial is superior. Everything from linear measurement to weight and temperature, the increments of Imperial are more accurate. I have this conversation quite often with one of our engineers who seems to favor the metric system.

You're going to have to explain this one.
 
Zero it at 25 with the sights set to 200. That should put you on paper at 200. By paper, I mean a full size NRA 200 yd target, not 8.5x11...

Trying to get more precision than that assumes you have ammo that meets the exact same specs as the manufacturer for muzzle velocity and ballistic coefficient and ignores the fact that the sight adjustments are really just designed to keep you on a man sized target.
 
Zero it at 25 with the sights set to 200. That should put you on paper at 200. By paper, I mean a full size NRA 200 yd target, not 8.5x11...

Trying to get more precision than that assumes you have ammo that meets the exact same specs as the manufacturer for muzzle velocity and ballistic coefficient and ignores the fact that the sight adjustments are really just designed to keep you on a man sized target.
Yeah, whether the rifle is capable of that or not, I'm not expecting that from the irons. Silhouette hits at 200 is good enough for me.
 
Plenty of army recruits have proved that irons are capable of hits on a full size silhouette out to 4-500yd with the proper training. On a one way rifle range, it's not really that hard.
 
natman, it's really self explanatory if you compare the two side by side.

How many degrees between freezing and boiling? 180 for imperial, 100 for metric. Which increment is more precise?

The kilo has approximately 2.2 units of measure for every one pound. Which unit has more precision between demarcations?

PSI has approximately a fourteen-fold refinement over kilograms per square centimeter.

I'm a machinist by trade, so let's say i want to bore a 3 inch hole, plus or minus three tenths of thousandth of an inch. 3.0000 +/- .0003 versus 76.2000 +/- .00762.
 
Status
Not open for further replies.
Back
Top