MOA for 1000 yards

[PHINPAD]

Can you help, I have been chasing myself around the Internet today trying to work this out but so far have just tied myself up in circles.

I am looking at purchasing a scope to go with a new rifle, which will be shot from 100 - 1000 yards. The IOR I am looking at has 50 MOA and I am not sure if that is enough but cant do the maths as they say.

Assuming that I have a base with 20 MOA, am shooting a 175 grain .308 at 2800 fps is that enough travel?

I would be interested in finding out how you come to the conclusion, if easily explained,

Thanks in anticipation.

 

[kentuckytroutbum]

A 20 MOA rail, or a 25 MOA rail (or mounts) may be enough. The way to do it is to go to a ballistic program such as JBM, and imput ALL of the required data to see what your drop is at various ranges out to 1000 yds. You will also need to know the amount of windage and elevation adjustment available for the scope you are intending to use. For example, I "zero" my rifles at 200 yds, and my Leupold VX-III 8.5-25x50 scope has a total elevation & windage range of 94 MOA (47 MOA left,right, down, and up from center). Based upon the drop, I decided to go with a 25 MOA rail for 1000 yd F-class shooting, which is roughly 1/2 of my scope's adjustment in one direction.

Once you run the ballistics and see your drop at various ranges, you can decide what MOA rails or rings to purchase. I would try to keep the knob twisting to a reasonable amount, and not use more than 1/2 of your scope's adjustments. IMHO

 

[woody_rod]

Just from memory, using a Palma load (155 grain bullet) the come ups are:

Point blank + 6 MOA for 300 yard zero
300 to 1000 yard + 36 MOA

In other words, total of 42 MOA. You would be pushing it with parallel scope and 50 MOA elevation. We use 20 MOA rail with no problems.

No need for a ballistic program. Use 20 MOA rail, load some ammo, go shoot.

 

[Laurie]

A 20-MOA rail is nearly always adequate for 1.000yd with these sorts of ballistics and your scope elevation range.

Assuming half that range - 25-MOA - is available with the scope mounted parallel to the bore, you have a total of 45-MOA adjustment to play with. In practice, you have to allow plus or minus 5-MOA, so 40-MOA minimum available.

Using Bryan Litz's G7 drag-curve based ballistics program (much more accurate than the bulletmakers' G1 based tables) for the Sierra 175gn MK at 2,800 fps, you'll drop around 34-MOA over a 100yd zero at that range and still be comfortably supersonic at around 1,200 fps (standard ballistics environmental conditions - 59F and 29.92" mercury).

That gives you a fair bit of spare adjustment. The full 2,800 fps MV is really necessary at this range though with a typical 175. You might consider a good 185 or 190 at 60-75 less fps that'll require a bit less elevation rise and keep your terminal velocties further up - important as you want to be running in the 1.3-1.0 Mach transsonic speed range as little as possible.

Laurie,
York, England

 

[kentuckytroutbum]

JBM's or Litz's ballistic programs are both valid. Laurie is correct in using the G7 drag profile is more representative than the G1 that the bullet manufacturer's use. Bryan has a good explaination of G1 and G7 in his blog site. According to Bryan, and I agree with him, G1 BC's look good from a marketing perspective, but are not realistic in the shooting world using BTHP bullets. JBM has a conversion program to calculate a G7 BC based upon the manuf. G1 BC. Also, you should run a ballistic program to see what wind drift will do to you at various distances. I print out a ballistic table for each of my loads ( assuming a 5 mph wind), tape it to the buttstock, and have it for instant reference when the wind starts to blow. You can extrapolate the wind drift if the wind exceeds 5 MPH.

Laurie's point about the transonic range is also valid. As the bullet velocity drops to almost Mach 1, turbulance will cause the bullet to destabilize, and accuracy will suffer.

 

[jr600yd]

Just a general rule of thumb that should get you on paper is:
from 100 yds to 600 yds come up 16-17 MOA
600 800 8
800 900 8
900 1000 6
So with a 600 yd zero come up 22 moa for 1K
Good shooting, Jim

 

[PHINPAD]

A Big Thank you to all who replied,

I will now purchase with confidence,

Regards

Dave

 

[fm1947]

if you have a rifle that you have adjuste the height knb all the way and you are still shooting low how do you adjust your scope to get it higher, will higher rings do this or what, I have read read and read some more about 20 moa base and all this other stuff but i am not sure about any of this , I do not have a problem yet dont even have a good scope just trying to look ahead at what i want to do so if i run into that issue i will know what to do. thanks

 

[Laurie]

If you run out of elevation adjustment, you only have three options:

(1) forget about shooting at that range.

(2) buy a new scope with an increased built-in adjustment range.

(3) cant the scope so it points downwards in relation to the barrel, either by putting shims under the rear mount, or installing a scope mounting rail or bases that have the rear end higher than the front, or by using Burris Signature Zee rings with nylon inserts of different thickness to cant the slope within the mounting rings.

When applied to bases / scope rails, this is usually referred to in terms of the effect on the scope in Minutes of Angle (MOA) which equates to 1.047" bullet movement at 100yd per MOA, and this multiplied proportionately at each further 100yd increment.

So, a 20-MOA angled rail will see a rifle shoot 20 X 10 X 1.047" higher at 1,000yd at any given sight adjustment = 209.4".

Whether you need a canted rail or sight mounts depends not only the ranges shot at and the scope's elevation adjustment range, but the cartrtidge's ballistics, hence the amount of additional elevation 'come-up' required over a 100yd (or whatever) zero to be correctly aimed. A modest .308 Win 155gn combination at 2,800 fps MV will need far more elevation increase to be correctly aimed at 1,000yd than a 6.5-284 say with a 139-142gn bullet at 3,000 fps.

There is often another advantage of using a sloped rail on top of getting additional elevation adjustment to reach the maximum range envisaged. It reduces long-range settings so they are closer to, or even on, the mid-point of the elevation adjustment range within the scope. Beacuse of the nature of scope 'erector tubes' that hold the reticles and their adjusters, they provide reduced and sometimes less accurate windage adjustments at the top and bottom extremes of their travel. An ideal situation is to have the elevation adjustment such that it is at its mid-setting at whatever is the key range for that rifle's usage.

Using higher rings does not change this situation at all, although it is a common misconception that it does.

Shimming the rear mount is the simplest / cheapest way of achieving the cant, but the least satisfactory. It tilts the rear ring in relation to the front and puts strain on the scope tube. If this method is adopted, it should only be done in conjunction with Burris Signature Zee rings with nylon inserts.

Any downsides? With a scope with limited inbuilt adjustment used on a very long-range rifle, the amount of slope needed to be 'on' at 1,000yd say can be such that the scope hasn't enough adjustment left at the other end of its travel - ie you cannot sight-in at 100yd because you've hit the bottom of the elevation adjustment range with it still shooting high. This would be unusual for most modern target scopes which have 50 to 60-MOA of internal adjustment available, unless the rifle was set up to shoot at ranges beyond 1,000yd.

Laurie,
York, England

 

[PHINPAD]

Laurie,

Another excellent and comprehensive answer, thanks. I look forward to meeting you on the circuit when I finally get out there.

Dave

 

[fm1947]

Laurie, thank you very much, I did not recieve a email to your reply , how do i do that?

Since I did not get your reply untill late I noticed many talking in here about the Burris ring , so I called then awhile ago , now I understand the whole thing and your reply was fabulous I know I will have more uestions as time goes on and I get closer to shooting, I am 63 years old and have read the history on F Class TR from what I read it was started in Canada for old guys . right up my alley, I have bees shooting Pistol for several years in USPSA and Steel Challenge, but my thought process is slowing down and so am I and those disciplines are about speed, so I search for something I my be interested in and found F Class Tr since I have a 223 and 308 I am at a good start I ordered a Weaver 36x Scope should be here today, I plan to try my 308 to start with it is a FNAR 20 inch heavy barrel, at the moment with a very cheap BSA 6x24x44 I am shooting some 1/2 inch groups at 100 yards , Martin at Burris said if I can shoot one inch at 200 this gun should be okay to compete and just have fun shooting, I have not shot rifle in many years but in 1966 I recieved the SAEMR, Small Arms Expert Marksmans Ribbon with M14. so I used to be able to shoot pretty good, we will see as time goes on how it all works out. Thanks again, how do i set this fora notification by email on replies? I will ck back later