Over the last few weeks I have been working on a formula to get a quick dope that is fairly accurate; within .1 or .2 mills of your true dope. I stumbled across this idea, and have been thinking for a while of trying to figure out a way to know my dope without memorizing it. I was quickly able to memorize 200, 300, and 400 yard dope but, past that I would continuously forget because I just didn’t study enough. This was only good for 200, 300, and 400 yard dope. What do I do at say, 550, without any kind of ballistic software? I was able to come up with a formula that is pretty accurate.
I have an inexpensive ballistic calculator, and I noticed a pattern. For the most part, for every 10 yards, my dope would rise .1 mill. I continued to run this out as far as I could, and while it did change further in distance, it still stayed relatively close. It made me wonder whether there was a way to come up with some type of formula to memorize dope that would be quick and accurate enough, even though it was only accurate out to a certain distance. Once I get into the 500 yard range, and definitely 600 yards, all the environmental aspects start making a bigger impact on my bullet. Therefore, I try to keep it within 500 to 600 yards. Being off a couple (.1 or .2) mils in the 200 and 300 yard range was not necessarily a huge deal, because it’s close enough for any kind of real world shot placement. However, in the 400 and 500 yard range, they can make a bigger difference, and the farther the distances the bigger the error.
So, this is what I came up with. Using my ballistic calculator for 500 yards, I wrote down the true dope between 500 and 600 for every 10 yards. I then subtracted a number that would equal the yards in distance. Or I should say one 1/100th Yards in Distance. This is what it looks like.
At 550 yards, my trued dope is 3.36 mils. I’ll round this up to 3.4. I’ll then take my distance in 1/100 yards and subtract 2.2. So 5.5 - 2.2 = 3.3.
3.3 mils is only .06 mils difference from my true Dope of 3.36. I can’t adjust for .06, so I have to adjust ether 3.3 or 3.4 mils. Ether way, I’ll have a small error of .06 or .04. The really cool thing is that this works so well with my 6.5 Creedmoor, that I can use this formula between 350 and 750 yards with less than a .2 mil error. For the speed that this gives, that’s awesome.
Let’s take a look at how large this error actually is. I’ll start with a formula. Please take note this can be useful.
1/100 range in yards divided by 2.777 multiplied by number of clicks (.1 mil) = number of inches bullet will impact
At 750 yards with a .2 mil error:
7.5 / 2.777 x 2 = 5.4 inches
If I’m only 5.4 inches off, that’s still within what is considered a clean shot on a deer’s vitals. It’s also still a hit on a 1 MOA plate.
Ok - let’s be honest; most people wouldn’t take that shot on a live animal, or wouldn’t have that opportunity at that distance. Maybe you only shoot out to 300 yards maximum. Guess what? You can tailor the formula to your needs. Just use your dope for 250 yards,
subtract whatever number from 1/100 the distance, and that’s the constant you use.
Ex. At 250 yards, my trued dope is .67 (.7 mils rounded).
1/100 of my 250 yard distance is 2.5
2.5 - 1.8 = .7
If you’re bad at math like me, an easy way to think of it is drop the 2 in 2.5 and add that 2 to your .5 which is .7.
Hopefully, I made this clear enough to understand. Now the real question is, why would you use this formula if you have a range finder and ballistic calculator? For several reasons. What if you forgot to bring them with you, the batteries died, or they got damaged? Maybe we’re going to be invaded by aliens and they set off an EMP and all electrics quit working.
Ok back to reality. It’s just a tool to store in your tool box if ever needed. Or, as I like to call it, “bag of tricks”. Use it to show off to your shooting buddies. With no equipment, tell your friend you can hit any target out to 500 yards before he can. Mill the target or guess the range, use the formula above, and win a drink. When asked how you could possibly do that, just wink and tell him luck. The more you know, the better shooter you can be.
Let’s look at the downside of using this formula. First, and probably most obvious, it doesn’t account for wind. I’m going to see if there is some formula like this one that will work for wind. If you know the wind is blowing to the left then aim to the right edge of the target.
Second, it doesn’t account for environmental factors. Well, here’s how I do that. My rifle is zeroed in standard conditions of 70 degrees Fahrenheit. If on the day that I’m shooting it’s 100 F, that means my ammo temperature and barrel is hotter, which means I should be getting a little bit more velocity. That means that my bullet gets to the target faster, and will impact higher. If I’m shooting in hotter temperatures, I may come down .1 mill to help accommodate for this. If I’m shooting when it’s colder, then my ammo temperature will drop. This means my bullet is not shooting as fast and will likely hit low. To accommodate for that, I may come up .1 mill. Is it perfect and precise? No, but the next time you’re at the range, give it a try. I think you will be very surprised how well this works, even if you completely miss, it should get you close enough that you can get a second round hit.
Below is a picture with different constants in a column for each one. As you can see, you can easily bracket every few hundred yard increments with a different constant, making this more accurate. Now you can actually use a constant between 100 and 300 yards, a different constant between 300 and 500 yards, and a third constant between 500 and 800 yards, to make this even more accurate for your bullet. Keep in mind, that past 500 yards, it’s going to be a lot harder to make a wind call with no equipment. I would recommend trying to minimize using this formula to about 500 or 600 yards. However, you can have decent success at longer ranges.
Another downside to this formula is that if you only use one constant, it doesn’t necessarily work extremely well with slower calibers. From the graph below, you can see that this is very effective between 300 - 750 yards with a 6.5 Creedmoor 147 grain hornady ELD match. This formula should work pretty well with any fast, flat shooting cartridge. With a 308 caliber, it is definitely limited. The curve of the bullet’s trajectory is much more significant. This means that this formula is not as accurate at distance with a single constant. But, with multiple constants and bracketing your yardage, it can still be quite useful.
I’ll quickly explain the bracketing aspect. Look at the second error column, from 200 - 300, I can use a constant of 2 to be very accurate (
less than .1 mills of error). From 300 - 400, I can change my constant to 2.1. This continues to give me less than .1 mills of error. From 400 - 700, if I use 2.2, I can still have less than .1 mills of error. For simplicity, I just use 2.2, but if I bracket, then I can get better accuracy.
Go to the range and give it a try. Maybe one day it can help.
The Overwatch
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