Posted: 1/9/2017 11:55:04 PM EDT
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So, for reference I'm thinking of buying a Vortex Viper PST 4-16x50 with MRAD reticle. This will be mounted on SW M&P10 .308.
Lets say I'm sighted at 100 yards and for a given load I'll be 62" low at 500 yards. If I understand correctly, to adjust the target turrets I would multiply drop in yards x 1000 and then divide by distance in yards. 62" / 36 = 1.72 yards x 1000 = 1720 / 500 = 3.4 (I did some rounding). So I would adjust the target turrets by moving 3.4 mils from 0. Is this right? Also, that's some annoying math to do in the field. Is there something I'm missing or do you just make a cheat sheet and take it with you? |
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Forget inches, you've got Mils.
My drop at 500yards is 3.4mils, I dial 3.4mils. You've got a Mil scaled reticle, so there's no point in thinking in inches and being like "hold 5 inches high on the deer" when you can either dial the turret or put the mil hold on the crosshair where you want your bullet to hit. My theory is that thinking of holds in inches came from the days when all you had was duplex reticles, and turrets were inconsistent. You couldn't rely on your scope to adjust, so you had to adjust where you put your crosshairs. Everyone (in America at least) knew what an inch was, so you knew your drop in inches, then could look on the target and estimate that many inches above where you want your bullet. With the consistency of turrets these days, and the invention of scaled reticles there is no use in thinking in inches or centimeters for holds. Either get some good velocity numbers, and a reliable ballistic calculator, then write down, or otherwise record your drops in Mils after verifying them. Your other option would be to get a taller target, don't dial anything and shoot. Use your reticle to tell how low your shot was in Mils (remember, scaled reticles are just rulers). Dial that same number just to verify, then write it down Also record your environment conditions, remember they can affect your trajectory quite a lot. Your math came to the correct answer, however the easiest way to do it is remember that 1 mil is 3.6" at 100 yards. Because it is an angular unit of measure, it increases linearly with the yardage. So take the hundreds number (or hundreds and thousands if you're past 1k) and multiply that by 3.6. Then take your inches and divide it by the previous number. Example: 62" low at 500 yards. 3.6*5=18 62/18=3.44. Because Mils it down to tenths, round to tenths. Or 3.4. Then you just dial from zero to 3.4 While this math is easier your best bet is to just create a Dope chart in Mils, and take it with you. You'd have to remember your drop in inches anyways. |
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Thanks. I see your point. Using a hornady calculator that has MRAD data I plugged in the data for the 165 gr sierra game king and here are a few numbers:
500 yards - 3.5 mils (close to what I calculated) 600 yards - 4.8 700 yards - 6.3 800 yards - 8.0 900 yards - 10.1 1000 yards - 12.4 Easy enough. Just have a cheat sheet in mils. Okay, one more question. The Vortex Viper PST has 21 mrad of adjustment. If I'm centered when zeroed at 100 yards then I'd have 10.5 mrad of adjustment which would get me out to 900 yards based on the above. Correct? Of course, I might not be perfectly centered so it could be a bit more or less. All things considered should I just get a 20 moa mount (assuming they don't make a mrad mount) for the extra adjustment even if I'm not likely to be shooting at that distance much? Looks like it would buy me about 6 mils of extra come up. Or better to stick with a flat mount? Or sight at 200 or 300 yards if I want to shoot that far? |
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Quoted:
Thanks. I see your point. Using a hornady calculator that has MRAD data I plugged in the data for the 165 gr sierra game king and here are a few numbers: 500 yards - 3.5 mils (close to what I calculated) 600 yards - 4.8 700 yards - 6.3 800 yards - 8.0 900 yards - 10.1 1000 yards - 12.4 Easy enough. Just have a cheat sheet in mils. Okay, one more question. The Vortex Viper PST has 21 mrad of adjustment. If I'm centered when zeroed at 100 yards then I'd have 10.5 mrad of adjustment which would get me out to 900 yards based on the above. Correct? Of course, I might not be perfectly centered so it could be a bit more or less. All things considered should I just get a 20 moa mount (assuming they don't make a mrad mount) for the extra adjustment even if I'm not likely to be shooting at that distance much? Looks like it would buy me about 6 mils of extra come up. Or better to stick with a flat mount? Or sight at 200 or 300 yards if I want to shoot that far? I would go ahead and get the 20 MOA mount so that you'll be able to dial it off without an issue. |
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Quoted:
I would go ahead and get the 20 MOA mount so that you'll be able to dial it off without an issue. So is there any downside to the 20 MOA mount? I read something about windage adjustment being limited if you are dialed down toward the bottom when zeroed. Not sure if that's true, but the theory was that because the scope is a circle the closer you are to edge vertically the less horizontal adjustment there is. Makes sense I guess. Also, I've heard the optical view is less perfect when zeroed far from center like the 20 MOA mount would cause. Can anyone confirm if this is a real issue and how much of an issue? Thanks. |
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Quoted:
So is there any downside to the 20 MOA mount? I read something about windage adjustment being limited if you are dialed down toward the bottom when zeroed. Not sure if that's true, but the theory was that because the scope is a circle the closer you are to edge vertically the less horizontal adjustment there is. Makes sense I guess. Also, I've heard the optical view is less perfect when zeroed far from center like the 20 MOA mount would cause. Can anyone confirm if this is a real issue and how much of an issue? Thanks. I have not had any issues with the two setups that I had with a handful of scopes. I'm about to upgrade the optic on another rifle and will be running another 20 MOA mount on it too. |
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Quoted:
So is there any downside to the 20 MOA mount? I read something about windage adjustment being limited if you are dialed down toward the bottom when zeroed. Not sure if that's true, but the theory was that because the scope is a circle the closer you are to edge vertically the less horizontal adjustment there is. Makes sense I guess. Also, I've heard the optical view is less perfect when zeroed far from center like the 20 MOA mount would cause. Can anyone confirm if this is a real issue and how much of an issue? Thanks. With good quality and well designed optics such as vortex you should have no problems. I run a 20MOA on my NF and have no issues. |
| I ended up ordering a basic 0 MOA vortex mount. On a related note, I'm assuming you could use the hash marks on the reticle to do quick hold over estimates. For example, at 300 yards if the come up is 1.5 mils so holding over 1.5 mils (i.e. using the 1.5 mil hash) would be the same thing. I'm thinking that in a hunting situation it might be easier and quicker to do this than dial it in. Also assuming if I ran out of adjustment on the turret I could also add in a couple more mils using the hash marks. For example, if I only have 10 mils to work with and needed 11 just hold over 1 mil after adjusting turret. |
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Quoted:
I ended up ordering a basic 0 MOA vortex mount. On a related note, I'm assuming you could use the hash marks on the reticle to do quick hold over estimates. For example, at 300 yards if the come up is 1.5 mils so holding over 1.5 mils (i.e. using the 1.5 mil hash) would be the same thing. I'm thinking that in a hunting situation it might be easier and quicker to do this than dial it in. Also assuming if I ran out of adjustment on the turret I could also add in a couple more mils using the hash marks. For example, if I only have 10 mils to work with and needed 11 just hold over 1 mil after adjusting turret. Yup, you've got it right. Good luck! I hope you enjoy your scope! |
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Great. Thanks.
One more question. Maybe should start a new thread, but it kind of fits here. When ranging, the math is not easy to do in ones' head. For example, say the body of a deer is about 18" high when viewed broadside and using my scope it subtends 1.7 mils (which would be a sort of guess as there is no mark for 1.7). If I understand right, the math is 18" x 27.77 / 1.7 = 295 yards. However, that math sucks (and I'm halfway decent at math). Do you just work out a chart ahead of time or is there a trick I'm missing? It's not much easier to convert inches to yards first but 18" is .5 yards so you could just divide 500/1.7 but even still not easy and only work for "nice" numbers like 18". What about something that was 13"? I guess what I'm working is is there a way to think about this too in mils? For example, if a deer subtends 1.7 mils adjust .5 mils. Obviously, you'd need to work this out ahead of time for a given load and its trajectory. Doing this would mean you wouldn't need to know range at all - just the known size of a given object and bullet trajectory. If that doesn't make sense, I'll see if I can work up a real example. |
| Search for "Mil dot range estimation card" in your preferred search engine. You should be able to find what you're looking for. Print out a card and get some 3M lamination sheets. You can attach it to your rifle, sling or keep it in your hunting pack. A reliable LRF would be more accurate, but this can get you in the ballpark provided that the animals dimensions match up with the reference chart/numbers (18" width etc..) and you can accurately measure the target. An error in either will likely result in a miss at extended ranges. Did I mention using a LRF? |
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I prefer to use yards instead of inches
18" is 1/2 yard as you said. .5 x 1000 /1.7 = distance The 1000 makes it simpler just move the decimal 3 places. So 500/1.7 = 294 yards With 13" inches you could just call it 1/3 yard because it is so close to 12" which is 1/3(333) or do math. 13/36=.361 or 361 for the formula. Obviously longer distances require more precise calclations, but once you start getting past 500yards you should get the range finder out anyway especially if you are shooting animals. |
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Thanks for the info. I wouldn't take a shot beyond 500 yards and in all honesty 200 or less would be most common. I can't see 200 yards through the trees around here anyway.
Mainly, it's just an academic exercise for me to help me understand how to use the an mrad scope. I've never had one before - just basic crosshair scopes. I found range estimation cards, but what I'm thinking is more a one stop shop combining both range and bullet drop for a given target and load. Bullet drop Dist come up in mils 2000.7 mils 3001.7 4002.8 5004.2 Target size at range 200 2.5 mils 300 1.66 400 1.25 500 1.0 So for a given measurement of a known target I could just reference size in mils and come up. If targets measure 2.5 adjust 0.7 1.66 adjust 1.7 1.25 adjust 2.8 1.0 adjust 4.2 I could make up cards like this for given loads and targets. Could even do it at 50 yard intervals. Obviously, they'd be very specific to a load, gun and target but would eliminate any in the field calculations. Or so I assume. Would this work? |
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Quoted:
Great. Thanks. One more question. Maybe should start a new thread, but it kind of fits here. When ranging, the math is not easy to do in ones' head. For example, say the body of a deer is about 18" high when viewed broadside and using my scope it subtends 1.7 mils (which would be a sort of guess as there is no mark for 1.7). If I understand right, the math is 18" x 27.77 / 1.7 = 295 yards. However, that math sucks (and I'm halfway decent at math). Do you just work out a chart ahead of time or is there a trick I'm missing? It's not much easier to convert inches to yards first but 18" is .5 yards so you could just divide 500/1.7 but even still not easy and only work for "nice" numbers like 18". What about something that was 13"? I guess what I'm working is is there a way to think about this too in mils? For example, if a deer subtends 1.7 mils adjust .5 mils. Obviously, you'd need to work this out ahead of time for a given load and its trajectory. Doing this would mean you wouldn't need to know range at all - just the known size of a given object and bullet trajectory. If that doesn't make sense, I'll see if I can work up a real example. @LRRPF52 should have something like this. His assistant instructor at his 2015 class had a tape on the elevation knob on his scope that corresponded the measurement to the distance to be dialed for an 18" target. For example 1.5 mils measured would equate to the proper elevation on the turret when dialed to 1.5. I may be remembering the details wrong, but that was the concept. |
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There is no reason to go through all that math, because you won't be able to do it on-demand out in the field unless you're a very small fraction of the population.
There are much simpler formulae that are just as accurate, but only require one function. What I learned from the Finns are the method above, as well as a fast mil relation formula. They use target dimensions in millimeters. TGT dims in mm / TGT dims measured in mils in the reticle = range in meters I made a conversion for this for yards. TGT dims in decimal yds / TGT dims in mils in the reticle = range in yards Decimal yards is TGT dims in " divided by yards, so 18" = 500 18 / 36 = .5 (500) 24 / 36 = .667 (667) So I see an IPSC (18" wide) steel silhouette through my scope. It's 1.2 mils wide. 500 / 1.2 = 417yds Anything 18" bigger than 1 mil is going to be closer than 500yds, and anything 18" less than 1 mil is going to be farther than 500yds. You can make this cave man relative by just using target relationships at different distances, like whether you can make out certain features or not. For ethical hunting, I prefer a laser range finder once you start getting past 225yds, as most centerfire rifle cartridges have a point blank zero of 225yds when you zero at 200. |