Rangefinders and slope angles

[grayfox]

OK, here's another question... out here in the east my regular rangefinder has been a good help - it's one that only does distance, not slope angle correction.
But out west the shots can be longer, and mountain slopes and/or up or down a draw, angles might be more of an issue. Should I get a rangefinder with slope correction? What ones does someone have experience with and would recommend?
I'm bracketing my range to be about 300-350 yds max.
Thanks.

[Wafavre2]

Sig

[A5BLASTER]

When I got into bowhunting a bought a cheap used Bushnell rangefinder made for bowhunting that gave range and slope and have been very happy with it, since then I bought there newest model that is made for use with a rifle and it has been spot on every time.

Tested it at the range, the range owner said his target boards were set at 100,200,300,400,500,600.

His range has a perrty good bit of down slope and when I ranged them they came out to 112,206,319,416, I told him and he didn't belive me so we taped them off and they fell dead on with what my range finder said they were.

It gives the direct line range and shows the slope angle and the true range with slope range included.

Hope this helps sir.

[ricsmall]

+1 on the sig rangefinders. I've borrowed and used everything from bushnells to leicas, some were better than others and most were grossly inconsistent at 400+ yds. Then I started hearing and reading about the sigs. So after all this time I finally bit the bullet and bought the kilo 2400ABS. Very consistent RF, I ranged road signs all the way out to 2309 last week. Now granted ,the one I have isn't for everybody as it's pricey, but does away with kestrels and ballistic apps. However, sig has models without the ABS, that will range out to 2200 I think, for much less. Hope this helps. BTW, before this one, probably the most consistent I used was an old bushnell 850 that I could range tree lines out to 900+, but not smaller objects.

Richard

[LR1955]

OK, here's another question... out here in the east my regular rangefinder has been a good help - it's one that only does distance, not slope angle correction.
But out west the shots can be longer, and mountain slopes and/or up or down a draw, angles might be more of an issue. Should I get a rangefinder with slope correction? What ones does someone have experience with and would recommend?
I'm bracketing my range to be about 300-350 yds max.
Thanks.

GF:

Before spending a lot of money you may want to see just how much your shots would go high given what you consider to be a difficult but doable condition.

I advise this because at 300 or 350 yards, you would be on a very, very, steep angle before a shot will go over a 8" kill zone. There are few places in the world where you would be able to take a shot on such a steep angle.

A 45 degree angle, for example, is extremely steep when in terrain. The difference between a 300 yard zero with no slope and a 45 degree slope is about two inches in ordinate given you estimate the distance to be about 300 yards. You would have to come down 3/4 of a minute on your elevation dial. Or you could hold a bit low in your kill zone.

May want to think about it before dropping a lot of money.

LR55

[grayfox]

55,
Thanks. It is that thought that makes me, so to speak, ponder. Most of my thinking on these things though is an exercise in self-talk unless I can get some inputs from other, more experienced shooters. A 30 deg angle, I think, is still pretty steep, and at 300 yds it reduces the horizontal to 259 yd, which for me and the rifles I'm planning to take, is 4.5-5" difference in drop. So, true, is it really necessary? And up to 10 deg I figure is pretty much a wash, so 10-30 deg... I don't know.
My current Nikon is a 6x magnif. with 550 yds, and that may be enough. I could always crank in -2" or so to the holdover if the angle feels more than 10 deg... kind of split the drop uncertainty in half for longer shots.
I appreciate hearing from y'all who have already faced this, though.

[LR1955]

55,
Thanks. It is that thought that makes me, so to speak, ponder. Most of my thinking on these things though is an exercise in self-talk unless I can get some inputs from other, more experienced shooters. A 30 deg angle, I think, is still pretty steep, and at 300 yds it reduces the horizontal to 259 yd, which for me and the rifles I'm planning to take, is 4.5-5" difference in drop. So, true, is it really necessary? And up to 10 deg I figure is pretty much a wash, so 10-30 deg... I don't know.
My current Nikon is a 6x magnif. with 550 yds, and that may be enough. I could always crank in -2" or so to the holdover if the angle feels more than 10 deg... kind of split the drop uncertainty in half for longer shots.
I appreciate hearing from y'all who have already faced this, though.

GF:

I think you need to be over 20 degrees before you may need to deal with adjustments of hold or zero. Its been a while since I had to deal with it so I could be off a bit.

One time I gave some serious thought about spending precious training time actually practicing steep angle shots. First I had to figure out how much slant range was necessary in order for us to actually see an effect. I could find steep places but in order to prove the effect, it had to be so steep we couldn't place targets without a helicopter and even then, we couldn't see the targets. Or the distance had to be so far with a lesser slant angle that any change to elevation based on true range was sucked up in a bunch of different variables such as visibility, range estimation error, wind doping, human error and inherent accuracy of the issued ammunition -- M-118 Long Range at the time.

One of the ranges we used gave us about a 10 or maybe a 15 degree angle and distance. I put in a steel at 600 meters and I figured that although the angle wasn't huge, the distance was sufficiently far that there would be a majority of teams who would have to come down or hold low to hit sils. I could have gone out more but if I had done so, things would have gotten too problematic to draw conclusions.

Well, 1/3 had to come down, 1/3 had to go up, and 1/3 were just fine holding center.

Not really a scientific test but sufficient for me to put things in perspective.

LR55

[Klem]

I agree with 55.

At 350yds you do not need a range finder let alone one with angle built in. That said, the SIG works for me. 350yds is just not far enough that the bullet drop requires careful calculation of slope angle.

For slopes up to 20 degrees you can just shoot as if it were flat and still be within a 3" radius circle of your zero (or in other words a 3" vital radius, or 6" vital diameter/zone).

If in doubt you can use a 5% ready-reckoner for both up and down slopes. That will compensate for all hills up to 30 degrees for this calibre. If you estimate distance-to-target and shave 5% off you will be within a 3" vital zero. For slopes over 30 degrees you can go 10%, bearing in mind 30 degrees is a pretty steep slope.



Note the drop for shooting uphill is almost the same as shooting downhill.

Calcs based on;
6.5mm 120Nosler BT @ 2450fps (for 350yds all average Grendel loads will satisfy the above).

You can do what-if's using the online JBM Ballistics program. Vary the Line of Sight Angle to mimic slope angles.

[grayfox]

This place is super!! Thanks to all for chiming in, K that's where I'm winding up, I may have to try the JBM - I have an early Pointblank and was using a cosine factor to correct to horizontal distances. And with some real-life results like 55 it does appear that any angular uncertainties would be overshadowed by the uncertainty of the nut behind the trigger.
I like that 5%-RR concept.
Now all I need is my GR barrel to get here for my bolt rifle conversion project... should be soon.
Again my respects to you all sirs!