Home Forums Hunting & Shooting Long Range Hunting Confused with my calculations?

Ok so after developing a load, and zeroing at 100 yards, I normally shoot it at 150, 200, 250, and 300 yards. I make notes of how many inches the bullet drops bellow POA at 50 yard increments for the purpose of manually calculating how many MOA of correction I need and assembling a drop chart.

The way I calculated this was by taking the drop in inches and dividing it by range, and multiplying by 100 to get MOA.

Example: at 300 yards my 165gr accubond drops approximately 13.5 inches

13.5 / 300 x. 100 = 4.5 MOA which is 18 clicks of correction to move the POI 13.5 inches.

This has always worked reasonably good for me.

However now I'm stretching out my 30-06 to 500 yards and decided to solicit the help of JBM ballistic calculator to get a more precise drop chart. However what I'm seeing in the chart it generated is close to what I observe on the range as far as bullet drop goes, but I'm not understanding how it calculates MOA.

For instance. At 300 yards it has my bullet drop at 13.1 which is close to the 13.5 I get. However it has MOA Drop at 4.2

When I do my calculation as above 13.1 / 300 x 100 I get 4.36 MOA which I would still dial in 18 clicks of correction. I guess I'm asking where did the .16 difference in MOA go. I know it's moot at 300 yards, but it continues on out to 1000 yards.

Have I been calculating it wrong for so many years? The difference I'm getting is small so I attribute me not seeing the difference in me not shooting out pass 500 yards. However I want to stretch it out so I want my calculations to be as exact as possible.

Not sure if I have understood your question correctly but remember that 1 MOA = 1.047 inches at 100 yards, and, put the other way around, 1 inch at 100 yards is 0.955 MOA.

The 1 inch = 1 MOA is a quick handy approximation that doesn't work as well at the longer ranges.

BriGuy,

I don't know if JBM is using MOA or inches but one MOA 1.04" inches at 100. I just call it 1" and one MOA for fun.

I understand MOA is actually 1.0471996 to be more accurate, we could carry that to infinity pass the decimal point if we wanted. 1.047 out to 1000 yards would be 10.47 less than .5" difference between calculating MOA on 1 inch or 1.047

My question is how did they calculate 13.1 inches being 4.2 MOA and not the 4.36 that I come up with? The formula I've shown above is the calculation I've used since my early years because that's the way I was taught to calculate it.

13.1/(1.047x3) = 4.17. JBM rounds MOA to the tenth, which means 4.2 MOA.

Prairie_Goat thank you. That's the answer to my question I was looking for. Nothing wrong with my calculation. Mine assumes MOA being 1 inch, so looks like I can still use it for the ranges my rifle was built for. (500 and less) but the formula you provided is the most accurate.

Thanks again kind sir.

Could also be an error in the altitude, temp, humidity etc... on the JBM Calc compared to your actually shooting location.

That would be a half inch at 1000 per each MOA involved.

I'm starting to realize that .47 difference at 1000 really adds up when you are coming up 30 MOA. I suppose even though in the back of my mind I always knew it, until I started to see it in a real world situation, you neglect to appreciate it. You don't see the difference as much in the ranges I'm limited to.

However I should point out that I typically do not shoot for groups at 400 yards. if I hit a 12 x 14 steel plate, I'm happy.

I would think an error in altitude, humidity, barometric pressure would give a flawed Bullet drop, but not in the way it calculates MOA. 1.047 is 1 MOA no matter the altitude. Example 13.1 is still 4.2 MOA no matter the outside conditions. Changes in real world conditions may alter the bullets flight path some what, but MOA is still MOA.

Curious why you would sight in dead on at 100 if you are wanting to shoot distance?

BRI,
Just a thought here, getting real world drops is always done best by shooting at the distances and recording that data. The differences in the JBM, the formula you used and the actual drop are negligible and given our propensity for movement in the gun, an errant breeze and any number of other factors makes those minimum differences in calculation irrelevant. If you are shooting a sporter and not a heavy barreled rifle it is difficult as humans to be completely steady and thus some on target deviation is normal.

Bill

"getting real world drops is always done best by shooting at the distances and recording that data"

+1

Too many people try to make this 'rocket science'!!

We're all so smart we have to make it difficult.

This!

Anyone the thinks the difference between inches per hundred yards and MOA isn't important over distance is just flat clueless about long range shooting. The difference is stark over 1,000 yards.

It doesn't really matter what the differences are. Simply enter your info into a program, print out your drops, then test fire at distance to confirm.

I know my drop for my 6.5 Swede is supposed to be 9.6 MOA at 600. I tested and it is actually 10 MOA.

This is correct if a scope adjusts inches per hundred yards that is fine, just use inches per hundred yards. If ones scope adjusts in true MOA one must be aware of the difference and use MOA data.
They can not be indiscriminately combined, is the point.

Because my rifle was purposefully built for 500 yards and less. No reason to not zero at 100 yards.

Yes sir, I would agree that inches vs true MOA is different past 1000yds..but how many can truly shoot accurately that far or even have a need to do so. And how many shooters can hold that .047 differential steady in how they shoot?
This not to enter into a flaming contest, just trying to point out that few shooters have the capability or equipment to accurately shoot out to where that .047 matters.
Bill

Hey Bill,

In the past I always went with real world drops out to 400 yards and calculated drop into MOA with the formula I provided in my opening post. This would be the first time I've gone to 500 yards. I've never stretched it out beyond those distances because I've never had an opportunity present it's self that would require me to shoot beyond 400 yards. All of my kills have fell within the 250 and less range. I shoot out to 400 yards at the range more or less because I enjoy it. I'm sure most can understand.

It wasn't until I decided to stretch it to 500 or perhaps beyond that I decided to punch my data into JBM and see how my actual drop coincided with a reputable calculator. There is when I discovered my discrepancy in MOA, or the way I calculated it. What you said about the differences at those ranges not being realized because of various factors is exactly the observations I've made in my own experiences.

I was more interested in the discrepancy between the MOA I was calculating, and what JBM was saying my MOA was. The differences wasn't enough so far at my modest ranges to make the difference between a hit or miss on steal plates. As stated above I don't shoot competitively so groups at those ranges mean nothing to me. I'm happy to wack a 12x14 plate.

I'm interested in going beyond 500, but not until I build my next rifle which will be a purposefully built long range rig. My rifle now is a printed Remington 700 action with a 24 inch #4 contour Douglass SS bedded in a Boyd's pepper gray laminate stock. Cerakoted action and barrel to graphite black. Topped with talley rings, and leupold vx3 3.5x10x40mm CDS. I do not wish to get custom turrets with BDC. I would rather dial my range in off a chart.

I limit my hunting shots on game to 250 until I become more proficient and or confident at extended ranges. I won't be rushed into a shot, or take a shot I don't feel with in reason will result in a clean kill.

Sorry if there are grammatical errors, typos, or if this reply just doesn't make much sense. I'm trying to do this on a iPhone. LoL