how to adjust for bullet drop

[roval]

I've been playing around with my savage mark II with a mil-mil scope. I have it sighted in for 50 yards and using a ballistic chart for wolf match ammo(the ammo I'm using ) it indicates a drop of 7.6 inches at 100 yds. I then adjust for 7.6/3.6=2.1 mils and I'm on target. Same with 150 yard with 25.6"drop=7.1 mils. but the 200 yards seem way off. it's a 55 inch drop on the chart does that mean to adjust 55/3.6= 15.2 mils adjustment from my zero or should it be 55/2(100s of yards)=27.5 then divide by 3.6=7.63 mils or just 55/3.6=15.2 mils. it's neither more like 12.7 mils to hit my target.
I'm now getting confused do you have to adjust for the hundreds of yards or just convert the drop in inches into mils or moas whatever your scope has?

 

[33rowdy]

I was trying to do the same thing. I believe for it to be "properly" done is with a chronograph with your gun. I have a box of 22-250 factory Winchester 45gr Jhp and in bold print it states 4000 FPS. Well I wonder if their gun is the same as mine? Barrel twist, barrel length, barrel smoothness and it goes on.

So if you don't have a chronograph like myself, Your best bet is to find the difference in drop from 50 yards to 100 yards with a chart, online calculator, or a good math wizard.

 

[esheato]

This is a 22 LR? How far do you really plan on shooting with it?

 

[Murphy4570]

This is a 22 LR? How far do you really plan on shooting with it?

Apparently to the point where having a forward observer is required, as you are now firing indirectly. :lol:

 

[roval]

it's a 22 lr. i'm shooting my spinner targets( this http://shop.sportsmansguide.com/net/cb/cb.aspx?a=798824) I shoot the smaller ones at 100 yards and the bigger spinner at 125 and 150(I pace the 125 and 150 yd distances) and 200 yds. you could see your hits since they spin.
Do you have to account for the distance (you know 1 MOA is 1 inch at 100 and 2 inches at 200) or do you just get the expected bullet drop in inches and divide by mils or moa and adjust your target turrets accordingly?
how far?-since the range is up to 200 and up to 225 where the gongs are then that distance. for fun. i do have a 223 i try shooting the 560 yard gongs with but it's less reliable making hits since i'm shooting with cheap ammo(silver bear) and wanted to get a 308 but i figured i'll just get a 22 bolt action where i could afford the match ammo and try doing the same adjustments but on a smaller scale.
i don't have a chronograph i found the wolf match ammo ballistic chart online. I had to hold off on my 200 yd shots since i ran out of elevation. i just bought a 20 moa base i haven't put on yet to see if it would help with it.

 

[SN13]

is your scope fixed power? if not, is it first focal plane? If not, are you increasing the magnification when going at 200yrd?

changing the magnification on a mildot scope that is not FFP, will change the actual drop accounted for by the mils.

Just trying to get to the issue.

 

[CraigC]

55" from a 50yd zero sounds about right, depending on the load.

 

[mrbro]

While the mil, or milliradian, is a constant angle, the actual on target distance is not constant at different ranges. 1 mil at 100yds is 3.6". 1 mil at 200 yds is twice that, or 7.2". 1 mil at 1000yds is 36". So 55" drop at 200 yds would be 7.6 mil. 55" at 1000 yds would be 1.5 mil. If you are having to dial in 12.7 mil to be on target at 200yds, your velocity is probably lower than what your ballistic chart presumes it is.

 

[WNTFW]

"I'm now getting confused do you have to adjust for the hundreds of yards or just convert the drop in inches into mils or moas whatever your scope has?"

simple:
Think of it as the adjustment for the distance is for the drop expressed in MOA ( Substitute Mils )

Simple yet confusing:
You are converting a relationship of the lengths of 2 sides (1 long & 1 short) of a triangle into a number representing an angle expressed in 60ths of a degree for MOA

Pick a range (Distance) to use for a baseline Zero. 100 for centerfire is good as 100 yd ranges are fairly well available. Zero for 100. Your elevation turret should be adjusted/calibrated to '0'. Now, if you know the projected drop from 100 to 200 in inches you can convert to mils or MOA. If you add 2-1/4 MOA to get to 200 you are zeroed for 200 @ 2-1/4 MOA. Your friend shooting the same load may have 2 or 2-1/2 MOA due to some variable including how the scopes track the clicks, height over bore or whatever. Just keep a table of yardages and the corresponding elevation corrections in whatever unit your scope uses as simple way to avoid conversions.

As far as predicting drops, shooting is the only way to verify 100%.

On my .308 I add 16-1/4 MOA for 600. (from '0' @ 100) 97.50" using easy math. When shooting at 600 I don't think about 97.5" I just start on 16-1/4 MOA and +/- elevation as needed to fine tune for the day.

It is nice to know what the 25 & 50 also if you only have access to a short range on a weeknight!

 

[roval]

thanks for the replies
re: the scope is a 4-14X BSA with a FFP reticle so the mils should be accurate for all magnifications but i was using it at 14x.

I think I understand now. you do have to account for distance, so get the drop in inches and divide by the hundreds of yard i.e 1.25 for 125 or 1.5 for 150 etc.. and then divide by 3.6 for mil adjustments. so it really should just have been 7.6 mils for the 55" drop at 200

or for a theoretical 308 zeroed at 200 yards with a drop of 51 inches at 500, it should be 2.8 mils right?

 

[benzy2]

In this game, as stated, an accurate muzzle velocity is very important. I like to use a program like Exbal using G7 BC rather than G1 BC to run rimfire calculations. It seems to handle them better than others. That should get you a good guess. The rest is adjustable based on what you see at the range.

Another issue to consider is the scope. BSA doesn't jump out as a scope that I would expect to track exactly as stated. I have a hard time believing it is tracking exactly .1 mil each click (or whatever the adjustments are) in a perfectly vertical track. Maybe it is, but it would be another point of concern for me, as I haven't had any luck with turrets on BSA scopes in the past.

 

[TCU]

consider the time of flight which is proportionate to gravity. Now the time of flight will variable due to air density which is a matter of temperature, moisture, and pressure. You must take this all into consideration when figuring out the bullet drop. Low pressure with warm and humid air will cause a bullet to drop less than a high pressure influence with cold dry air. It all has to do with TOF. Also drop can be further influenced by wind direction and spin direction. If you have a wind blowing from the left the projectile will impact low right as opposed to a right wind with an impact high left. This is due to a pressure gradient force around a projectile. You can get a good ballistics program which takes all of this into consideration.

 

[Vern Humphrey]

it's a 55 inch drop on the chart does that mean to adjust 55/3.6= 15.2 mils adjustment from my zero or should it be 55/2(100s of yards)=27.5 then divide by 3.6=7.63 mils or just 55/3.6=15.2 mils. it's neither more like 12.7 mils to hit my target.

If you are starting with zero elevation (that is, the bullet always hits low, at any range) then you can make your adjustment in Mils. If you already have some elevation cranked in, you'll have to allow for that.

A Mil is 1/1000 of the range. Two Hundred yards is 7200 inches. Each Mil would then represent 7.2" at 200 yards.

 

[helotaxi]

I like to use a program like Exbal using G7 BC rather than G1 BC to run rimfire calculations.

That's interesting considering that the G1 standard form is very much like the standard .22LR bullet while the G7 is a VLD (long ogive with boat-tail) design.

 

[henschman]

You can't ever count on the data on the box being correct for your rifle... it would vary a bit with barrel length, altitude, etc.

The best way is to dope your elevation adjustment by shooting paper targets at increasing distances. With a .22, I'd probably start at 25 yards and then move back in 25 yard increments, firing at least a 5-round group at each distance. Adjust until you are on target. Record all adjustments you make, as well as the atmospheric conditions (wind, temp, humidity if you can, lighting conditions). You will probably get out to about 300 yards before you run out of scope elevation. When you are done, you will have all the come-ups for that ammo in that rifle. It is a good idea to tape a piece of paper with your come-ups to the stock.

Remember, if you don't write it down, it didn't happen!

 

[benzy2]

That's interesting considering that the G1 standard form is very much like the standard .22LR bullet while the G7 is a VLD (long ogive with boat-tail) design.

Whoops, said it backwards.

 

[chaser_2332]

If your scope is mil/mil stop thinking in inches, get a rough drop chart in mils and start shooting, make fine adjustments as you go. Spot your misses and adjust accordingly, that's the best part of matching retical and adjustments

 

[roval]

i do have the info now taped to my stock.with the explanations from the previous posts at least i now know how to anticipate adjusting the scope for ballistic info i got from the internet knowing full well my mileage may vary because of my different shooting conditions.

 

[Jenrick]

Lets say you're engaging a target at 276yds away, and hypothetically your data tells you the drop at this distance is 84".

Take your range, and figure out how many inches are in it. In this case 9936 inches, divide that by 1000 to figure out what distance a mil subtends, in this case 9.936 inches. Simply divide your drop (84") by the mil subtension (9.936) to figure out how many mils 84" equals at 276 yds. 84/9.936=8.4541, so call it 8.5 mils.

Now if you do your work in metric it becomes a little simpler as 10cm = 1/1000 of 100m, so .1 mil is 1 cm at 100m, 2cm at 200m, 3cm at 300m etc.

-Jenrick

 

[Chuck Dye]

Playing with the Oehler Ballistic Explorer sight adjustment calculator and borrowing a B.C. of .130 found at http://www.6mmbr.com/rimfiretactical.html (worth looking at) and muzzle velocity of 1050 and assuming a 1.5 inch sight height, I get the following:

50 yard zero sight angle equals 10.79 MOA

100 yard zero sight angle equals 18.07 MOA

150 yard zero sight angle equals 27.07 MOA

200 yard zero sight angle equals 37.07 MOA

Which differ a bit from the 6mmbr.com figures.

All ballistics calculations are, at best, starting points for testing specific to the individual rifle, ammo, and shooter and, for the hard core, the individual ammo lot numbers. In other words, a good excuse to shoot more.

Conversion of MOA to milliradians is left as an exercise for the student.

 

[Buck Kramer]

Every gun has a limit. 200+ yards with a .22 is not impossible, but it is impractical.

 

[helotaxi]

Lobbing .22LR rounds into a soda bottle WAAAAAY out there can be fun though. Took me 40 rounds to get a hit at 400yds. The slightly variable winds and the inconsistency of the cheap ammo I was shooting made it that much more sporty.

 

[ball3006]

Just take your rifle to the range and shoot it to see what it does at different ranges. All 22 ammo is not created equal nor are the rifles. Theroy is great but it is the practical application of bullets that is important.....chris3

 

[roval]

actually it doesn't look like it as way off as I thought. I had the turrets add 5.2 mils in elevation and then held off for 7.5 slashes but looking at another scope, I
may have been counting the slashes for a half mil as a full mil instead in which case it would have come out at 8.95 mils. still off but closer to the theoretical 7.6 mils from the ballistic chart. next time i'm at the range i will measure how much my 1 mil adjustments move my bullet but that won't be till next week.
the shooting with a 22lr at that distance was not for any practical reason other than being familiar with adjusting the scope for anticipated drops and fun. when it did hit it, it hit it consistently. I had attached an orange 1 1/2 inch target to the center of the upper and lower paddle of my bigger spinner(original ones had disintegrated long time ago). when i had a string of 5 continuous hits at both the upper paddle and the lower paddle both were shot off when i examined it during the next ceasefire.
next time i go I will be rezoing the scope as i'll be putting a new 20 moa base.

 

[roval]

thanks chuck dye. that where i got that chart i was using for the wolf ammo.
i am shooting in Albuquerque and it's probably more than 5000 feet altitude at the range(i'm guessing) compared to the 1000 feet they used for the chart.