Diagnosing long range errors: Bad RF?

[JakeC]

Has anyone had trouble with a rangefinder giving crisp, confident, but incorrect readings?

I have an athlon 1 mile RF. I'm now pretty certain that it's off, but I want to cover my bases. I'm reading 550y on a target that was (by gps) around 620 and reading 760y on a target that was evidently 800-810. (Accidentally switching meters/yards and not noticing doesn't correctly account for the difference.)

For reference I'm using it on steel plates/chain/pipe assemblies completely surrounded by grass. No rocks, nothing else I could hit that would give clear, infinitely repeatable results.

for context: I had a crummy afternoon practicing yesterday, shooting miserably, consistently low. I was trying to practice acquiring, ranging, and hitting out at long range. Either 1) my RF is reading 40y closer than reality 2) my MV/BC are wildly incorrect (2 loads of 4 have been verified before, the other 2 were developed with choronograph this year.) It didn't occur to me to open Onx and measure until I got home, but I guess I don't quite know how accurate the straight-line measurement is. Probably very accurate, I just don't know.

Anyway, just wondering if anyone's experienced the same thing. I looked for quite a while but only saw a few posts about failing batteries from a long time ago. Almost all RF problem searches bring up no-reads or golf. Battery is the easy button but my gut tells me something else is going on. Trying to figure out something around town that has known distance in the meantime.

 

[Ryeguy]

Can you borrow a friends range finder, or a couple and see how the compare. Or go find a road and measure off your odometer and do some math.

 

[Rick Richard]

The difference is not due to any inclination by the way?

 

[JakeC]

Can you borrow a friends range finder, or a couple and see how the compare. Or go find a road and measure off your odometer and do some math.

Both good ideas, but the only guy I know with a RF I trust has been incredibly ill and couldn't find it last time I asked anyway. And my odometer is probably off due to my tires. I'd have to verify with Onx, lol.

The difference is not due to any inclination by the way?

As in slope? no the RF accounts for that, gives both readings: it was about .5 y difference. 50 feet in 800 y, not much.

 

[dfanonymous]

The issue is usually user error. Specifically in the reticle vs back drop if you have one.

Go find a telephone line and get some distance. Like 600y or more. You want the sky as your backing. Then aim directly at the line. If it doesn't read anything, then try all 4 quadrants of the reticle. Chances are it will be true in one of the those quadrants. That's your true aiming point.


If it's not that, and you have obstacles such as brush, then your RF might being picking that up through beam divergence. I'm not familiar with your particular unit, but there should be an option for first or second reading. You'll have to get spin up on that, if you're not already familiar.

If it's none of those, then it's just a garbage rangefinder. To explain, the rangefinder shoots a laser and reads the reflection back on a timer. It happens in microseconds, but if all else is well, and your rangefinder is still off then, that's a design flaw in the computer….

 

[eshell]

The issue is usually user error. Specifically in the reticle vs back drop if you have one.

Go find a telephone line and get some distance. Like 600y or more. You want the sky as your backing. Then aim directly at the line. If it doesn't read anything, then try all 4 quadrants of the reticle. Chances are it will be true in one of the those quadrants. That's your true aiming point.


If it's not that, and you have obstacles such as brush, then your RF might being picking that up through beam divergence. I'm not familiar with your particular unit, but there should be an option for first or second reading. You'll have to get spin up on that, if you're not already familiar.

If it's none of those, then it's just a garbage rangefinder. To explain, the rangefinder shoots a laser and reads the reflection back on a timer. It happens in microseconds, but if all else is well, and your rangefinder is still off then, that's a design flaw in the computer….

This is an excellent suggestion. I have always checked laser RFs by doing essentially the same thing, but by checking a post with the RF correctly oriented to see L/R error, then turning it sideways to check vertical error. None of mine and very few of my students are exactly behind the reticle.

 

[lancetkenyon]

What I usually do in Flat land scenarios with an object on a plane, is set my LRF to "Near" and shoot over the target and slowly pan down. Yardages will continue to change until you hit the target.

Also, mounting the LRF on a tripod makes a HUGE difference. Only way to go when hunting pronghorn.

 

[JakeC]

The issue is usually user error. Specifically in the reticle vs back drop if you have one.

Go find a telephone line and get some distance. Like 600y or more. You want the sky as your backing. Then aim directly at the line. If it doesn't read anything, then try all 4 quadrants of the reticle. Chances are it will be true in one of the those quadrants. That's your true aiming point.


If it's not that, and you have obstacles such as brush, then your RF might being picking that up through beam divergence. I'm not familiar with your particular unit, but there should be an option for first or second reading. You'll have to get spin up on that, if you're not already familiar.

If it's none of those, then it's just a garbage rangefinder. To explain, the rangefinder shoots a laser and reads the reflection back on a timer. It happens in microseconds, but if all else is well, and your rangefinder is still off then, that's a design flaw in the computer….

It's a little fussy but it has in general passed this test, including a few minutes ago. Like I said, the truest point is sort of the bottom of the reticle, but when tehre's a huge difference in media it's going to pick up the strong signal throughout the reticle. Ten minutes ago it agrees with onx to the yard at 486 to the stop sign at the bottom of the hill, and it's within a couple yards of being the same on a phone pole up the mountain at 775-ish. That one won't pick up the pole as consistently. At 680-ish it can read a pole from the top to the bottom, but I can't find that one on satellite to compare. Both views are unobstructed, as were teh targets.

Also both targets yesterday were on slopes facing me on the opposite side of a drainage. They were surrounded by very wispy, seed-headed grass that I struggled to get a signal back from by itself. I feel very confident that I was picking up the targets, not the grass 20-50y down the slope closer to me. One was across a jeep trail cut into the slope so there was a pretty strong jump there when I could get a signal. I mean, I'm open to mistakes and have observed what you're describing in the past, but not dozens of yards in open space.

And I can't replicate it in the same conditions now, lol. I'm at a loss.

 

[JakeC]

yeah, it's only 6x which I wanted for archery, but it's pretty squirrely on the desert. But I can still usually pick out individual rocks at 600 or so. And hit them, generally. Especially in staggered, layered terrain. I don't know what is going on now.

 

[JakeC]

The issue is usually user error. Specifically in the reticle vs back drop if you have one.

Go find a telephone line and get some distance. Like 600y or more. You want the sky as your backing. Then aim directly at the line. If it doesn't read anything, then try all 4 quadrants of the reticle. Chances are it will be true in one of the those quadrants. That's your true aiming point.


If it's not that, and you have obstacles such as brush, then your RF might being picking that up through beam divergence. I'm not familiar with your particular unit, but there should be an option for first or second reading. You'll have to get spin up on that, if you're not already familiar.

If it's none of those, then it's just a garbage rangefinder. To explain, the rangefinder shoots a laser and reads the reflection back on a timer. It happens in microseconds, but if all else is well, and your rangefinder is still off then, that's a design flaw in the computer….

If it's useful, this is what I was looking at. The one on the right looks more obscured than it was, but the nearer hillock is at about 400y instead of "550", so that would stick out. The one on the left is super open. Could it have been dirty or a lighting issue? Both were completely unambiguous and repeatable. Appreciate the insight.

 

[willfrye027]

Could be the RF…hard to get an accurate reading in flat terrain and high sunlight.

How confident are you in the actual 100 yard zero? If it's not dead nuts on, you may be introducing some additional error at distance there. I like to see the bullseye obliterate at 100 yards with a high number of shots 10-15 or so ideally. Then you know you've got a true 100 yard zero and can eliminate that potential source of error.

 

[ShtrRdy]

It might be related to the beam dispersion of the LRF. If the beam is wide at the location you were measuring, you might be picking up that little rise in front of the targets.

 

[JakeC]

Could be the RF…hard to get an accurate reading in flat terrain and high sunlight.

How confident are you in the actual 100 yard zero? If it's not dead nuts on, you may be introducing some additional error at distance there. I like to see the bullseye obliterate at 100 yards with a high number of shots 10-15 or so ideally. Then you know you've got a true 100 yard zero and can eliminate that potential source of error. View attachment 574880

That is second on my list o fthings to chase down. The answer is that I'm not very confident. Kinda did it in a hurry with a bad setup. All 3 rifles got rescoped and I forgot to zero them well during load finalizing. I usually prefer the zero to be about a click high, maybe 2 if MOA, to be very sure the planes are intersecting. But if it's a hair under will that amount to 20y, 40y difference? Asking because I'm not sure. All 3 rifles being roughly the same distance off... Hard to say.

It might be related to the beam dispersion of the LRF. If the beam is wide at the location you were measuring, you might be picking up that little rise in front of the targets.

Sorry, tried to make it clear, but that little hill is 200y closer than the closer target, it would have been obvious if I was reading that. They were both on unobstructed slopes. I could have been measuring closer, because I know the thing is off a little, I just was only getting those readings because the terrain wouldn't signal, as in I couldn't range past the targets or to the side.

 

[dfanonymous]

If it's useful, this is what I was looking at. The one on the right looks more obscured than it was, but the nearer hillock is at about 400y instead of "550", so that would stick out. The one on the left is super open. Could it have been dirty or a lighting issue? Both were completely unambiguous and repeatable. Appreciate the insight.

View attachment 574879

GPS is not a good reference. GPS is accurate but the average gps is only accurate to 16 ft. At best. It can get worst.

As far as brush, you'll only know if you try it on between 1st and second priority. If you have it on the wrong mode, it could thing some stick out there is you primary target.

Are you using a tripod?