Range Report Shooting angle questions

[shootermark]

I'm new to long range shooting and I’m trying to understand the complexities of shooting long ranges and certain angles that are involved.

What are the benefits of 20moa scope mounts? I have a straight non moa scope mount for my Rem 700 and my shooting buddy has a 20moa scope mount. Side by side the slope on the 20 moa mount is very negligible compared to my straight mounts. At what range am I getting the additional 20 moa? Is there a simple mathematical formula I can figure this out with? At 100 yards what are the differences between the two bases.

My second question deals with canting my scope when shooting at really long ranges. A small cant of 1 degree will move my bullet impact how much at 1000 yards. Again, is there a simple mathematical formula I can figure this out with? How much will a 5 degree cant move my impact at a 1000 yards.

Thanks everyone, hope my questions weren’t too bad for a first post.

Mark

 

[HH4]

Re: Shooting angle questions

With your zero MOA base you may have to use up a lot more of your downward elevation adjustment in order to zero, which will leave you with less available total elevation travel in your scope. You might find yourself in a situation where you have run out of elevation adjustment when shooting at longer ranges depending on how much elevation your scope has. So the advantage to the canted base is that you will have more available elevation travel.

 

[Scott R]

Re: Shooting angle questions

If a scope only had 30 moa of elevation correction from it's zero when mounted on a 0 moa base then it would have 50 moa correction with a 20 moa base and all else the same.

As for the impact change with a given cant, it will vary dependant on the amount of drop from line of sight, or arc of trajectory. I wouldn't worry so much about how much change with a given angle as I would in trying to avoid cant.

 

[shootermark]

Re: Shooting angle questions

Thanks so far for the couple of responses. I understand my questions fairly well or I guess to a point. What I'm really looking for are more detailed answered and better yet the mathematical calculations for the angles questions and what the equate to.

With such a slight incline/angle on the 20 moa base how am I getting 20 more moa, and at what distance will I get the full 20 moa? I can't figure out how it's possible and haven't figured out a calculation for it.

With the cant issue, my question is really two fold, though I'm looking for the calculation also. What really got me thinking about this was an artical I read on shooting 1200 yards or more and how a cant of even 1 degree on your rifle can really mess up your bullet impact. Then I saw a few posts here on canted reticles and that really got me thinking about my questions and how would or could I calculate for that.

Thanks again for any help here.

 

[MALLARD]

Re: Shooting angle questions

im not expert , but if your getting 300 in drop , and you cant 1 degree , the impact will miss by around 5 inchs. There is more horizontal shift when canting , vs vertical. For cant , the best thing is to just eliminate it.

I cant give you any formula's. I am sorry.

you need a caliper to measure the differences in slope moa rails , even then the difference is slight, but a 20moa rail would move 1/3 of 1 degree, pretty small change.

Its my understanding moa rails are really making the most out of your sight adjustments, If you have 50 moa of total adjustment in your scope, and you get a zero with a flat base, more then likely you will only have 25-30 moa of usable adjustments left for drop , the other 20moa would be useless, getting a cant base would allow you to get a 100y zero at the higher end of your scopes adjustment range, allowing you to make more use of the total adjustment range of your scope.

 

[Scott R]

Re: Shooting angle questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: shootermark</div><div class="ubbcode-body">Thanks so far for the couple of responses. I understand my questions fairly well or I guess to a point. What I'm really looking for are more detailed answered and better yet the mathematical calculations for the angles questions and what the equate to. <span style="color: #FF0000">1 moa equals 1.047" per 100yds </span>

With such a slight incline/angle on the 20 moa base how am I getting 20 more moa <span style="color: #FF0000"> Do the math...20moa equals .0698" per foot, or to relate closer to the length of a scope base .0349" per 6"(that is the difference of the approx gap on a lawn mower spark plug from one end of the scope base to the other) </span> , and at what distance will I get the full 20 moa? <span style="color: #CC0000"> all distances, the angle remains the same to infinity </span> I can't figure out how it's possible and haven't figured out a calculation for it.

With the cant issue, my question is really two fold, though I'm looking for the calculation also. What really got me thinking about this was an artical I read on shooting 1200 yards or more and how a cant of even 1 degree on your rifle can really mess up your bullet impact. Then I saw a few posts here on canted reticles and that really got me thinking about my questions and how would or could I calculate for that. <span style="color: #FF0000"> Until you grasp how the scope/base combination works to allow the line of sight to be adjusted to intersect with the bullet's trajectory at given distances there is no point in stressing over the calculations of cant error. </span>

Thanks again for any help here. </div></div>

 

[GOING FOR 2000]

Re: Shooting angle questions

700P-.308
That is why I use a Horus Falcon Scope with H-37 reticle, Zero at 100 yds then shoot the mil grid. No knob turning.

Did put a 20 moa rail on my windrunner, but still zeroed at 100 yds and shot the grid. When I zero it for 1000 yds it puts the reticle almost in the center of the scope tube and lowers the mil hold number for 2000 yds.

Get a anti-cant level (US optics), mounts on scope rail, you can check the level of your weapon with a glance. Forget the math, too many other things to calculate when shooting ELR.

Night force Ballistic Program has an input for up or down angle shot, read the angle and input it, will be corrected in the hold result.

 

[shootermark]

Re: Shooting angle questions

Scott,

Thx for your reply answer. I'm betting I'm not the only one here that thought 20 moa bases were giving me 20 additional moa adjustments on my scope as that is really not the case. I was thinking I'd get an addtional 20 moa of adjustment at a 1000 yards.

This is why I was struggling with the calculations. Can you help with the cant angle calculations?

Thanks again, Mark

 

[Greg Langelius *]

Re: Shooting angle questions

What may seem negligible is not.

Most rifles will reach 1Kyd with the right bullet using somewhere between 30MOA and 40MOA of elevation over and above the 100yd zero. FYI, 30MOA translates to 1/2 of a degree.

My scopes have 75MOA of elevation adjustment travel, and that's quite a bit for a scope. In practice, that translates to 1 1/4 degrees.

Many scopes don't even have half that. Combine that with the fact that many of them won't zero at 100 without using up at least/around half of that adjustment, and the 20MOA boost the sloped base can give becomes not just substantial, it often becomes essential.

I often custom bed my bases to provide the 100yd (or closer, as with .22LR's) zero at or around 5MOA up from dead bottom of the vertical adjustment travel. This practice can occasionally result in an effective base slope of 30-35MOA, but the outcome is that I now have roughly 70MA of elevation travel actually available for real-time usage.

Now understand that I'm likely never going to be shooting at distances where such elevations are needs, but at 1Kyd, the 28-32MOA my rifle needs puts the elevation adjustment right about smack dead center of the adjustment range.

Since we know that windage adjustment range becomes highly restricted as one approaches either end of the elevation range, this custom relationship puts the elevation adjustment right where the windage adjustability is at its very least degree of restriction.

Crazy like a fox, eh?

Cants...

All cants are significant, and all cants are especially significant at extreme distances. But some cants are bad, and some, not so much. It's my rule of thumb that if it's noticable, it's worth fixing. If you can notice a 1 degree cant, you're a better man than I am, Gunga Din, and the logical offshoot of all this is that you can even get it perfect, and still be subjecting the rifle to a shooter induced cant that outwighs any small errors that scope mounting might be slippin' you.

If your shooting at 1200yd and a 1 degree cant puts you off by an unacceptable amount, this means that youve got all the other variables nailed better'n most BR shooters can manage.

Hey I love precision as much as the next guy but let's be practical. Damned few of us, maybe myself especially, can shoot so danged good that a 1 degree cant is going to be the issue that wrecks our day.

If sweatin' things is your thing, don't sweat the small stuff; there's plenty enough bigger stuff to keep ya busy.

For starters, there's wind... I'm still hung on that first one...

Greg

 

[shootermark]

Re: Shooting angle questions

Greg,

I was focusing on the fact that Leupold factory specs say their scopes can be off by as much as 3 degrees, not to mention when we shoot prairie dogs we've never paid attention to our rifle set up and I cant the heck out of my rifle. Now that I'm reading all this great information and I'm seeing where we've been doing things wrong, I'm focusing on the little things now and trying to understand this.

Do you know the calculations for cants angles and what they amount to at 1000 yards.

Thanks, Mark

 

[Greg Langelius *]

Re: Shooting angle questions

Honestly, no. I go by my 'rule of thumb', do my best to keep the reticle level, and internally agree to accept whatever inaccuracies this and all the other intangible/insurmountable issues will permits me in the way of accuracy.

A world champion shooter once told me it was reasonable to accept 1/2MOA of accuracy from a really good gun at 100yd, and 2MOA from the same gun at 1000yd.

I believe him to this day.

To me, there are a lot of variables, and only some are amenable to human improvement. I try to be practical about it, try to figure out the realistic priorities, and adopt a philosophical approach to perfection.

I say 'approach', not 'achieve', where perfection is involved. The difference between a happy shooter and an unhappy shooter isn't in their targets, but in their goals. Stay realistic, and you'll be happier. Sometimes I shoot like crud, but given conditions, etc., I still tend to be at least sorta-happy. Those 'put-'em-on-the-wall' targets are not the norm, and I think a lot of us still don't really comprehend that simple, basic reality. Been doin this plenty longtime now; and I'm beginning to figure out the philsophical parts, I am...

Greg

 

[maladat]

Re: Shooting angle questions

Since I am bored I will take a stab at this. Lets say your cant angle (scope twist about its own long axis) is T (degrees, with cant of the top of the reticle to the right being positive and to the left being negative). Your amount of dialed elevation on your canted scope is E (up is positive, down is negative) and dialed windage is W (right is positive, left is negative). E and W can be angular measurements (MOA, mils) or length-on-target but both must be the same unit and that is the unit you will get out of the equation.

Effective elevation is E*Cos(T)-W*Sin(T).
Effective windage is E*Sin(T)+W*Cos(T).

Let's do some examples!

With no wind at 1000 yards you might dial 35 MOA up elevation (366.5" on target).

With a 3 degree scope cant, you get effective elevation of 35*Cos(3)-0*Sin(3)=34.952 MOA (365.9" on target). You get effective windage of 35*Sin(3)+0*Cos(3)=1.832 MOA (19.2" on target).

Now at 100 with the same elevation but enough wind for a 7 MOA right windage adjustment (73.3" on target).

Effective elevation is 35*Cos(3)-7*Sin(3)=34.586 MOA (362.1" on target). Effective windage is 35*Sin(3)+7*Cos(3)=8.822 MOA (92.4" on target).

Scope cant really screws up your windage. It doesn't do as much to elevation.

This of course has NOTHING TO DO with 20 MOA bases.

 

[Scott R]

Re: Shooting angle questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: shootermark</div><div class="ubbcode-body">Scott,

Thx for your reply answer. I'm betting I'm not the only one here that thought 20 moa bases were giving me 20 additional moa adjustments on my scope as that is really not the case. I was thinking I'd get an addtional 20 moa of adjustment at a 1000 yards.

This is why I was struggling with the calculations. Can you help with the cant angle calculations?

Thanks again, Mark </div></div>

Mark, the 20 moa scope is allowing just that, an additional 20 MOA of elevation adjustment in the "UP" direction.
Here, I'll try again. Let's assume you have a rifle/base/scope combo happened to be zeroed at 100yds with the scope internals at it's mechanical center, and the scope happened to have 60 moa total travel (30 moa up and 30 moa down). Now you start shooting farther than your "zero" and adjusting your scope knob in the "UP" direction to allow the line of sight through the reticle to line up with the trajectory at that distance, when you reach the distance that your ammo has dropped 30 moa further than it's 100yd trajectory ( and your scope is adjusted "UP" 30 moa) you have reached the mechanical limit of your scope. If you want to shoot farther and still be able to adjust the reticle to match the point of impact, you can replace the zero base with a 20 moa base. Now from your initial 100 yard zero you will have 10 moa "DOWN" and 50 moa "UP" of travel in the scope's internal adjustment.