Sighting in 308

[zobster]

Hi guys quick question, assume that I've zero-ed my rifle at 100m, and based on the numbers given by the manufacturer.

0" at 100m
drops -4.3" at 200m
drops -15.5" at 300m

Would the bullet impact 4.3" high or low on a 100m target assuming that I have dialed in the 4.3" drop into my scope (approx 2MOA, 8 clicks).

also, does it mean that if I zero it at 200m, it would drop 11.2" at 300m?

[handofcod]

The trajectory isn't linear so drop depends on velocity and the projectile. Try 1.5inches high at 100m, should be bang on at 200 (or so).

[Shorti85]

I'll be following this thread. I need to sight in my .308 after I break it in

[David Brown]

I mean this……watch these video's over and over until it makes sense.

https://www.youtube.com/playlist?list=P ... F0EC711484

Rather than give you the answer….give you the education. Ryan is the guru of not only shooting but teaching. Enjoy!!

[rsj223]

I'll be following this thread. I need to sight in my .308 after I break it in

If all go's well I should be firing the first shots through my .308 tomorrow

[Shorti85]

I'm going out tomorrow morning to go and break mine in. So much cleaning but not enough shooting involved. But I'll take my .22 to have a bit of fun with in between

[Shorti85]

I managed this photo today

[Sam45]

Great Photo

[Shorti85]

Great Photo

Thanks

[1290]

Hi guys quick question, assume that I've zero-ed my rifle at 100m, and based on the numbers given by the manufacturer.

0" at 100m
drops -4.3" at 200m
drops -15.5" at 300m

Would the bullet impact 4.3" high or low on a 100m target assuming that I have dialed in the 4.3" drop into my scope (approx 2MOA, 8 clicks).

also, does it mean that if I zero it at 200m, it would drop 11.2" at 300m?

4.3 inch drop at what range??
If zeroed at 100m and then dial in 4.3 inches at 200m (a bit less than 2MoA, but call it 2), would raise the point of impact at 100m by the ratio of the distance which would be 1/2 or 2.15 inch...

200m zero would drop a bit less than the trajectory drop from 200 to 300, or less than 15.5 - 4.3 = 11.2, maybe 8ish inch plug some numbers into a ballistic calculator.....

With a scope, 100m is far too close a zero IMO, to best utilise the trajectory of the round, whether or not you use the dial-in or Max point blank range method, 200m to 230m+, ballistics dependent is more useful.

& just to get the discussion going, Trajectory of ANY bullet is determined by ONLY two factors; the BC (ballistic coefficient) and the muzzle velocity. nothing else. provided both launched at the same velocity, a 22 cal will have exactly the same trajectory as a 30cal or a 50cal providing the bullets have identical bc...

[zobster]

Hi 1920,

I understand the part about trajectory of bullet is only affected by BC and muzzle velocity.

I think I understand what you are saying, will confirm what I understand at the range this weekend.

[1290]

if you state the load, I can give you some more info.... brand, bullet mass, velocity...

[SendIt]

Hi guys quick question, assume that I've zero-ed my rifle at 100m, and based on the numbers given by the manufacturer.

0" at 100m
drops -4.3" at 200m
drops -15.5" at 300m

Would the bullet impact 4.3" high or low on a 100m target assuming that I have dialed in the 4.3" drop into my scope (approx 2MOA, 8 clicks).

also, does it mean that if I zero it at 200m, it would drop 11.2" at 300m?

No, it's not linear as handofcod said. It's easy enough to work out though if you can tell us what you're shooting. What ammo is it?

I can give you a few figures in the mean time using some average figures, this is for a 155gr boat tail at 2,900fps MV which will be about right for most ammo.

100m Zero
100......0
200......-3.3 drop
300......-12.1 drop
400......-27.4 drop

200m Zero
100......1.6 rise
200......0
300......-7.2 drop
400......-20.9 drop

300m Zero
100......4" rise
200......4.8" rise
300......0
400......-11.3 drop

[brett1868]

Trajectory of ANY bullet is determined by ONLY two factors; the BC (ballistic coefficient) and the muzzle velocity. nothing else.

Don't hate me but I have to politely disagree with this statement. Many forces can influence a bullets trajectory and include, gravity, aerodynamic drag, air pressure and wind with secondary considerations of spin drift, coriolis effect and the steepness of the incline. Also worth a mention that global position and shot bearing also have an influence but near enough to zero for regular hunting distances. Modern ballistics programs can take all that data and compute a trajectory with a degree of accuracy. To be fair to 1290 a lot of these factors don't really come into play till you're getting out past 500m but they do have impacts on trajectory however minor at shorter ranges.

As for the zeroing of scopes at a particular range I've always used 100m no matter if it's the .204 Ruger or Barrett 416 and the reason for this is that it's less susceptible to environmental effects including wind then a long range zero. Also the standard deviation of muzzle velocity of the ammo plays a part on longer zeros as 10-20fps SD at 100m isn't going to open the group up much but at 200m it'll have an effect, minor as it may be it's still an effect that can be eliminated. By setting a zero at say 200m one day then shooting at 200m on a different day with different wind speed and direction the zero will shift a lot more then if you had zeroed at 100m. Since a reliable zero is critical to accuracy it's wise to zero at a shorter distance and remember to check it often. I generally check mine each trip away just to be sure nothings changed, usually I only need to adjust zero between summer and winter due to a change in air density / temperature. Some of the old school fox hunters had different loads for different seasons so they didn't have to adjust their scopes.

If we look at the longest sniper kills, out to 2400+ m they are nearly all shot at a reasonably high altitude where the air is thinner and the drag lower which allows for a flatter trajectory for the same BC and muzzle velocity due to the projectile staying supersonic longer and thus remaining more accurate over those distances. Put the same sniper at sea level on a cold day with the exact same rifle and round he'd have a challenge getting close to the target using the same dope on the scope so trajectory can vary based on environmental effects.

If the original poster could provide the projectile make, weight & type along with muzzle velocity there are several members here who would be only too happy to run it through a ballistic app and post you a table.

I use a combination of Field Firing Solutions from http://lextalus.com/index.htm
And
"Applied Ballistics" PC version from https://store.appliedballisticsllc.com/ProductDetails.asp?ProductCode=DL2001 or there's an online version at http://appliedballisticsllc.com/ballistics/ or search the Apple store for "AB Mobile".

Ref
"Accuracy and Precision for long range shooting" by Bryan Litz. Chapter 7 "Accurate Shooting Basics", Chapter 9 "Trajectory Modelling"
"Applied Ballistics for long range shooting" Bryan Litz Chapters 1-7

[1290]

Hate you? I'm a lover not a hater.. .

Anyway, that was the most polite disagreement Ive seen around here with my statements in a long time....

Trying to keep it simple, then you bring in Mr Coriolis

All things equal.... only 2 variable determine the trajectory.... hows that
Yes, environmental factors came into play, pressure, temperature, gravity variations (really only when comparing significantly different elevations), but not the drag of the proj - all shape and mass factors are covered by the BC(at fixed enviro conditions..).

But yes, if you shoot at sea level as opposed to the top of Mt Everest, the temperature, pressure and gravity differences will come into play. if however you're comparing a 30 cal with a BC of 0.6, launched at a mv of 3000fps to a 50cal of same BC and velocity, and a 22cal at same, same.....

At the same location, direction and inclination/declination.... at the same time, then I stand by my original hypothesis

[brett1868]

I'll agree that all else being equal, BC & Velocity are the only 2 factors in play

[Old Fart]

Don't hate me but I have to politely disagree with this statement.

Polite disagreement?!

Who the hell do you think you are!!!

[BBJ]

Trying to keep it simple, then you bring in Mr Coriolis

It effects more shooters than you realize.

I didn't know realize either, but all the guys with Remington 700 Tacticals shooting at 100m are constantly talking about it so it must be a factor at even that distance...............

[brett1868]

Trying to keep it simple, then you bring in Mr Coriolis

It effects more shooters than you realize.

I didn't know realize either, but all the guys with Remington 700 Tacticals shooting at 100m are constantly talking about it so it must be a factor at even that distance...............

Wait till they start talking about the Eotvos effect, Magnus effect and the Poisson effects and that's only with external ballistics. We can then open a Pandora's box of effects relating to interior ballistics and even transitional ballistics...with all these exotic effects it's astounding I can hit the side of a barn at 50m.

[zobster]

Hi guys quick question, assume that I've zero-ed my rifle at 100m, and based on the numbers given by the manufacturer.

0" at 100m
drops -4.3" at 200m
drops -15.5" at 300m

Would the bullet impact 4.3" high or low on a 100m target assuming that I have dialed in the 4.3" drop into my scope (approx 2MOA, 8 clicks).

also, does it mean that if I zero it at 200m, it would drop 11.2" at 300m?

No, it's not linear as handofcod said. It's easy enough to work out though if you can tell us what you're shooting. What ammo is it?

I can give you a few figures in the mean time using some average figures, this is for a 155gr boat tail at 2,900fps MV which will be about right for most ammo.

100m Zero
100......0
200......-3.3 drop
300......-12.1 drop
400......-27.4 drop

200m Zero
100......1.6 rise
200......0
300......-7.2 drop
400......-20.9 drop

300m Zero
100......4" rise
200......4.8" rise
300......0
400......-11.3 drop

I understand what you are trying to say.

The place is go shooting has a flat spot of about 100m long, thus I can only realistically zero to 100m.

What I'm trying to say is, after dialing in the 3.3" drop (approx 1.5MOA) at 200m where are my shots going to land at 100m. 1.5MOA higher?

I'm a budget shooter so I'm shooting only PPU .308 winchester 165gr SPBT 2675MV. they group surprisingly well in my HOWA1500, all within a 50c piece @ 100m.

[brett1868]

I'm shooting only PPU .308 winchester 165gr SPBT 2675MV. they group surprisingly well in my HOWA1500, all within a 50c piece @ 100m.

That's some of what I needed This might seem a little strange but there's no guarantee of a bullet drop between 100m & 200m, in fact it's possible to get a rise. The projectile will traverse the line of sight twice in its trajectory due to scope height. I understand what you're after and I don't mean to over complicate it, I just want to give you a drop table that's as accurate as possible.

Can you measure from the centreline of the scope to the centre line of the bore and let us know the distance please

[zobster]

Hi Brett1868,

I guess you are after the scope height. It's approximately 42mm.

My goal is to use the 100m "range" to "zero" my scope at 200m. I figured that if I zero it at 200m, all my shots taken from 100 to 300m is all going to be within +/- 6" of my point of aim.

[1290]

You can use a +/-3inch mpbr for a zero at somewhere around 200 to 230m zero, maybe a bit more, first trajectory cross may be around 20 something metres - thats your zero which will be identical to the 200 odd metre zero, dont worry about 100m....

[Chronos]

You can use a +/-3inch mpbr for a zero at somewhere around 200 to 230m zero, maybe a bit more, first trajectory cross may be around 20 something metres - thats your zero which will be identical to the 200 odd metre zero, dont worry about 100m....

This^^^

Get it 1.5-2" high at 100 then hold dead on from zero to 230-250m or near enough.

Chronos

[brett1868]

Table below based on some research and assumptions. Good out to 500m, I can re-compute and post longer distances if you like. Chronos is pretty well spot on the numbers, first x around the 20m mark then 2nd at 200m. 200 hold dead, 100 aim 2.77 inches low. Elevation in this app is backward to me as it is giving the elevation of the projectile rather then what you need to dial into the scope. Test out the numbers and let us know how close they are, though if you want a more accurate plot then the round needs to be run over a chronograph and the appropriate wind / temp / humidity etc etc entered.

Zobster.JPG (149.36 KiB) Viewed 12119 times

[1290]

Time for some 'visuals' fellas, this is based on the ppu data for the 165gr 308 load, purely graphical. I have superposed the adjusted +/-3inch MPBR trajectory on to the stated 150zero traj.....

ppu308win-165gr.gif (18.24 KiB) Viewed 12106 times

You can see the first trajectory cross, it would be less/closer if the scope mount height was lower than the 50mm (ppu stated). If you're using this MPBR of 246m, the zero would be 210m.

If you plug in the data and manage to fit it to the ppu info, you may get differing results

[lole]

So many charts

[North East]

Just shoot the thing and get over this data....work it out for yourself.

[pomemax]

http://www.huntercourse.com/ranges/riflerange.aspx
have a look at that site

[headspace]

For a 308 used as a hunting rifle with the majority of hunting shots taken within 300m I put mine an inch and a half high at 100m then it's dead on at 200m. I know exactly where it will print at 100 and so if it's windy I can work out where it will hit at 200m or even 300m. But I'm using 165gn bullets which work best in my rifle and have an excellent BC. People using things like 110gn bullets in a 308W will find it very difficult to hold zero past 100m if a wind is blowing. My load has been chronographed at 2,750fps 2m from the muzzle.
JD