Ranging Practice discussion thread (spoilers)

[LemmyCaution]

I like MOA better myself.

I guess if you're going to measure distance in something as archaic and impractical as inches, feet and yards, you might as well really shoot the moon and measure angle in MOA.

I like math… but not that much.

 

[sscoyote]

Man--i love it. Would've liked to have seen the little 27" army men on top of the TMR reticle closer to the .2 mil stadia lines to get a more accurate interpolation. Actually got 333 once i knew the tgt. dimension (not bad for interpolating both sides of the tgt.). Got 896 on the thousand yarder, but was happy about that due to the inaccuracy of the system (for me at least) beyond ~500-600 anyways as well as 2-sided interpolation as well.

Don't understand how to post a pic though to get the answer into a ghostlike format..?

 

[taliv]

so post number 5...

interesting challenge. i figured the target was 2/3 larger than it ought to be, so i measured it as 2 mil wide (though it looks kinda funky like it's at an angle or something) so i figured that was 1.333 mil. 1/3rd of a yard high divided by 1.333 mil * 1000 gave me 250 yrds. but if i did that on height, using 2/3 of what looks to be about 1.6 mils, gives 312 yrds. hmm...

 

[LemmyCaution]

Post 5:

Step 1: De-Americanize the units: 12" = ~0.3m
Step 2: Un-ass the SFP scope: 12/18 = .666
Step 3: Estimate target width = 2mil
Step 4: Apply un-ass factor: 2(.666)= 1.332
Step 5: Math (0.3/1.332)1000= 225 meters

This is apparently wrong. So the target is 12" what? High? Wide? Viewed from an oblique angle after three beers while squinting?

Let's try 12"H. I estimate 1.65mil (I think I see 0.05mil of rock sticking down below the crosshair).

1.65(.666)= 1.1
(0.3/1.1)1000= 273 meters (298 yokel meters)

There we go.

 

[sscoyote]

Well done--nothing wrong with using 2nd FP reticles for rangefinding, especially since about 99% of us use them. It teaches an important concept of the inversely proportional nature of subtension vs. magnification. Besides that rangefinding is more accurate at a higher magnification and smaller subtension. If all the user has is a 2FP scope then he may as well know how to apply it. In fact i have used the mil-reticle in a 2FP optic at 32x to reverse mil a tgt. of known dimension to calculate a subtension in order to reverse mil a 1000-yd. target to obtain it's dimension, and guessed it to within .3" of it's true dimension.

The target is setting at a slight angle, but from my calcs on this 1 and others it doesn't seem to be enuf to make a difference.

BTW, the .05 below was absolutely correct. Excellent observation!

Just noticed that width doesn't seem to work on this one, and i don't know why as it is a 12" disc.

 

[baldeagle93]

Just noticed that width doesn't seem to work on this one, and i don't know why as it is a 12" disc.

I think it is because the target is at an angle which is giving you an inaccurate mil reading.

I guess if you're going to measure distance in something as archaic and impractical as inches, feet and yards, you might as well really shoot the moon and measure angle in MOA.

I don't think that anyone here would be considered a "Metric Martyr," but the "impractical" imperial system is what we are used to. The target is at the same distance not matter what, you have to do math to get the range.

 

[LemmyCaution]

The target is at the same distance not matter what, you have to do math to get the range.

You just have to do a little MORE math in the American system (We don't actually use the true Imperial System. the UK does) Actually, kind of a lot. Actually, too much, unless you just let the computer take care of the whole thing. And how ironic that a country like ours uses the facets of the king's anatomy as the basis for our measurements. But I mean really… An inch is ~0.02778 yards! A foot is 0.3333333333… yards! Preposterous!

Full disclosure: I speak the American system very well. I work in the trades. But I also used to manufacture power systems for the oil and gas industry internationally, and I have to say that the SI system is far superior.

There's almost nothing more silly than a decimal inch. Almost, meaning a metric foot. I once received a truss system from a manufacturer in the UK. The overall lengths of the truss sections were in even metric increments. The weldment of the truss webs, center to center, was in feet. The results were comical (Q: 'how many feet fit in 2 meters?' A: 6, remainder 6.74 inches). But the manufacturer insisted that their product was not merely of the highest quality, but 'superior.' And not just superior to this or that, but just simply 'superior.'

 

[MCMXI]

sscoyote,
Here's what I get with your 12" high target.

milrad (vertical) = 1.55 but reticle calibrated for 12x not 18x
18/12 = 1.5
milrad_actual = 1.55/1.5 = 1.03 milrad
12" = range(")*0.0013(radians)
range (yards) = (0.0013/12")*(1 yard/36")
range = 322.6 yards

On closer inspection, I'd estimate the vertical subtension to be 1.60 milrads rather than 1.55 milrads. This would result in 312.5 yards ... not a bad estimate.

 

[sscoyote]

Excellent. Kinda' nice when it works. Must be the angle that is actually making the difference between height and width. I'm certain that i measured the vertical along the face of the plate at 12", but it could be oblong. I'll check it again next time i go out to the range. We also have another couple plates set at 425 yds. again at an angle. A buddy was checking his MD-reticled 3.5-10x Leup. M4, and it wasn't coming out right. I looked through it and got just short of 1.2 mils at a guess of 1.18-- 18 x 100 / 3.6 / 1.18=424. Worked perfect and my buddy about fell off his bench.

LC-- Don't understand what the big deal is here. Heck man we're just calculating ranges to tgts. using a reticle. It's not like we're paying the mortgage--relax.

 

[Maverick223]

I once received a truss system from a manufacturer in the UK. The overall lengths of the truss sections were in even metric increments. The weldment of the truss webs, center to center, was in feet. The results were comical...

I don't doubt it, a friend of mine worked on a bridge project with metric specifications (design), the construction (being performed in the US, WV IIRC) was performed using the imperial system [head slap]. Several errors (blunders) led to major sections of the work having to be demolished and rebuilt...a very costly mistake that could have easily been prevented by using the same standards for measurement in the design and construction. It turned out something like this (obviously not the actual project, but a good, if exaggerated, example):

 

[Dimis]

How'd I Do?

are we going for exact or just rounding it?

 

[baldeagle93]

LC,

how ironic that a country like ours uses the facets of the king's anatomy as the basis for our measurements

Could not agree with you more! I mean we fought for independence through the revolutionary war and we forgot to change one important facet of our freedom...freedom from

silly decimal inch.

Just poking fun...I actually agree with you, but it is the standard for America and when in Rome...

Mav has a very good point and I just alluded to it...standard. It should not mater if you were measurements are taken in cubits as long as you are using it as a standard. Just my humble opinion...I could be wrong, it happened once.

 

[Maverick223]

It should not mater if you were measurements are taken in cubits as long as you are using it as a standard.

Yep, which leads to a good point...the adjustments should absolutely match the reticle...No Matter What. If you like to turn knobs in MOA, no problem, get an MOA reticle...like Milling reticles, get Mil knobs to match.

 

[MCMXI]

taliv,
I was +11 yards on the left plate (est. 0.3 milrad) but +133 yards on the right plate (est. 0.25 milrad)! An error of 133 yards at that range is significant.

 

[taliv]

man, nice work on the first one! that's close!

i posted 2 more, btw

 

[MCMXI]

taliv, are you sure about the target in post #10? Either way, this method is not proving to be too accurate for me and I used a ruler this time.

Post #8: +33 yards on the right target and +110 yards on the left target

Post #9: +97 yards

Post #10: +445 yards

Post #11: -160 yards

 

[Grump]

Taliv:
I really don't buy it on the 1000 yard target, second to last of of today. Post #10, September 25, 2010, 07:17 PM. I see the 12-inch square as being a bit *more* than the 0.5 mil hash mark. I called it .6 mil.

.333 yard target (1 foot square) divided by .6 mil = .555 x 1000 = 550 yards. Or are those .25 mil hash marks and I'm 10% off on the mils? Or is there an undisclosed SFP discrepancy?

It would have to subtend .333 mil to be at 1,000 yards, by my math.

Please 'splain.

I GOT the one with the SFP set at 18 power...IN MY HEAD, no calculator!.

 

[taliv]

Hmm. Could be wrong. We shot that plate from lots of distances and angles up to a mile away. I was taking pics with my iPhone and had no way to label them until I got home. So yeah it's entirely possible I mixed one up. I'll look them up Saturday and verify.

Great work on the rest especially considering the quality of photos

Edit. One thing to note with my pics is that I'm not always square to the target so if it is at an angle it could appear narrower than it actually is making it appear further away but vertical should be correct

 

[taliv]

Doh! You guys were right. We shot that at 1020 yrds from one stage and 585 yrds from another. I put the wrong value in the main thread and will fix it shortly. The correct range is 585

 

[blackops]

All I have to say is I wish targets were that clear at 1000yds in my scope. It would be an entirely different ball game.

 

[taliv]

man, good luck with challenge in post 15! anyone who gets within 10% will deserve a cookie for sure.

i was right on measuring the dude in post 14 vertically, but i'm way off when i measured him horizontally.

 

[~Ace~]

On the Last Pic I get 800, 860 and 900 using my new Ipod App.

 

[taliv]

wow, Ace, that's pretty close!

what ipod app lets you do that??

 

[B1gGr33n]

Man I've got lots of learning to do lol

 

[taliv]

I can't wait to see who gets the bonus target in post 21!