Reply With QuoteI assume it's ok to post this great link on here?
http://www.anstonftc.co.uk/targets/
Registered User
Advice on calculating Hold-over/under mil dot distances
Hey all,
I am fairly certain this post is in the wrong place but I can't post it anywhere else so do move if necessary.
I am looking for some advice on how people figure out the distance of each mil dot in their scope for making hold-over/under shots. Is it just trial and error test work or can a scientific formula be applied with relatively accurate results? If it is trial and error, what would the best setup be to do the figuring out? any advice offered will be greatly received.
The rifle and scope in question here are the HW100kt lam and the Hawke Airmax 30 4-16x50. I typically zero the scope at 25 yards to make working with MOA simpler, Having recently spent time learning about minutes of angle and how to zero a scope mathematically.
Registered User
I assume it's ok to post this great link on here?
http://www.anstonftc.co.uk/targets/
Even a stopped clock is right twice a day
If you download the Chairgun program from the Hawke website, it has settings for calculating mildot intersections - obviously it is mostly tailored for Hawke's own mildot systems, but I believe they have a generic one on there as well.
It goes without saying that you'll need to test it yourself to confirm, but it's a good starting point.
Good deals with these members
Systems Administrator
I'm all for using BCs and velocities to work out aim points, but nothing like a bit of practical testing.
If you want a good day out then nip down to the range at Rifleman Firearms.
They have an enclosed 60 (might be 90) yard range with auto target return so you can set your target out at any distance.
Aim at the bull and note where they go on your reticle. Then using this new aim point double check you hit the bull.
Then you can spend the rest of time hitting targets out to 90 yards on their very target rich range
This is a video from about 2 years ago, they have added even more targets since then.
AND in the same complex is a smokery that sells fantastic smoked meats and treats. Make sure you are there for lunch
Registered User
I think the only accurate way to do this is to shoot paper at the ranges you are interested in.
Chairgun is good, but only as good as the data you put in.
For example my TX200 holdovers wouldn't match up with anything chairgun said UNLESS the ballistic coefficient of the pellet was changed. That led to some googling which is when I found out the ballistic coefficient of the pellet is determined by the power plant (spring/PCP/CO2) and to a lesser extent the individual barrel on your airgun. So the default values don't always work.
Having said that, Chairgun is really good for testing adjustments to scope height or zero range etc. Provided you have correlated the chairgun numbers, with actual tested numbers, first.
In term's of carrying out the test, Charub's link is perfect if you want to use true mil-dot magnification (usually 10x). If you want to use a different magnification, you will need to adjust the size of the targets.
Systems Administrator
I'm sure Jim Tyler did an article about changes to BC of the same pellet. Velocity can also have an effect (at least it does with fullbore) so the BC can change as pellets slow down at longer distances.Originally Posted by cooper_dan
Registered User
Thanks everybody. This is all superb information for me to start digesting.
I believe I need to go away and understand what ballistic co-efficient actually is and how it can vary before I get deeper on holdovers and the like. That said, I will have a play with the Hawke Chairgun app now....
Rifleman's Firearms sounds like a location directly form heaven! smoked meats and rifles! only an hour away from me too so will have to check it out pretty soon.
I am a note taker, so if there is interest, I could write up my learning and experiments after I get down the range and do this.
tlhIngan maH. taHja
The link to Anston is very good. It loos like the work of Brian Samson.
Mil dot is pretty rubbish for calculating range as it is really a military system based on the average man height.
It is a good idea to get a load of A4 paper print outs with a large vertical cross + and put them out at set ranges from 8, 9, 10, 11, 12, 15 20 25 30 35 40 45 50 and 55 yards.
On a piece of paper, draw your ret with the + and the mil dots.
Shoot the target with the scopes cross hair on the centre for each range and you will see how the pellet stike changes as you go from 8 yards to 55.
Just mark the distance on your piece of paper.
Redo this onto some paper or waterproof material with all you POI's marked.
Mildots will only work when the magnification is set just right - typically 10 x but not always. This is where the print off from Anston helps as it will allow you to adjust your mag ring to the ACTUAL calibrated mag where the mildot scale is correct and not what the mag ring claims it is...the two can be very different.
If your doing HFT set the focus so that 40 yards is JUST slightly out of focus and that 45 is even more so.
You will also have a similar crossover point closer too say 15Yards. That way, if the image is slightly or very blurry, you know if your target is Under say 15 or 40 yards or further.
Higher mags narrow this depth of field and there is a balance as to how much mag you need Vs how blurred and unhelpful the image is.
If its for FT, then you will probably be using a very high mag scope and mil dots are pretty much for me.
You really want a fine ret with mil an sub mil substensions for more accurate placement. MTC's SCB ret is a really good ret for air rifles either HFT/FT or hunting and much copied.
I have shot comps and hunted with a 30/30 ret, mil dots and everything inbetween, but the SCB ret is a great favourite and does its job very well indeed IMHO.
I would not go back to Mildot.
In a battle of wits I refuse to engage with an unarmed person.
To one shot one kill, you need to seek the S. Kill only comes from Skill
Registered User
Well it varies
When you change the scope mag the holdover per dot will change, it also varies with different pellets & muzzle velocity.
To use Chairgun accurately you need to chrono the rifle & set the scope height correctly you also need to zero for the longest, flattest PBR & even then it's only actually shooting at the specified ranges that will confirm the data Chairgun gives you is correct.
Mushroom Man
Yes, Chairgun is an excellent start point but, in my opinion, you then need a bit of range time to fine tune the dots ... or parts of dots. Open air is good if you have a no-wind day but even a slight breeze can produce horizontal and vertical movement depending on the location / terrain. But again, you will get good indications. I know people who visit indoor ranges e.g Pete's Airgun Farm (?) just for this type of facility.
Cheers, Phil
Registered User
Another point I forgot to mention in my earlier post. I know Chairgun works for some people, but for me it absolutely will not correlate with my HFT setup.
I don't know how chairgun deals with BC at different distances as the pellet slows down. Maybe someone cleverer than me will say. But if I used the chairgun holdovers for this gun, I wouldn't hit anything past 35 yards.
But my S410 in 0.22 matches up perfectly.
World FT Springer Champion 2014
The problem with doing all of this mathematically, is that you'll end up making assumptions and entering incorrect values.
As an example - where did you get the BC for your pellet? - it will be an average that can vary massively from shot to shot, and from one batch of pellets to the next. The figures often quoted are average figures.
If you've read up about mathematically zeroing by minutes of angle - I guess you'll be making the assumption that your scope clicks actually are 1/4 Moa. They aren't.
Similarly when you go to using mildots, you'll probably be making an assumption that your scope has true mildots at 10x mag - it won't.
All that adds up to a whole heap of errors and assumptions - and it's the reason why people will often say that Chairgun is wrong. It can only be as accurate as the information it's being fed - Garbage In, Garbage Out.
Even zeroing by shooting at paper at set distances isn't foolproof - parallax error, cant, wind, poorly grouping pellets, bad technique, cylinder fill pressure, dirty barrels etc etc. Can have just a disastrous effect on the results as the errors and assumptions made in Chairgun.
Registered User
This!
If I zero at the beginning and end of a session they usually wont match up. It takes me 20 or 30 shots to get warmed up before I can worry about getting any good results.
I've started doing more regular holdover testing and will be keeping the data from all of them. Never hurts to have more information.
World FT Springer Champion 2014
It uses a profile for a projectile shape. Usually "GA" which gives it a curve of how the BC is likely to change with drag/velocity (it's by no means a straight line).
Registered User
Personally, using maths is a waste of time, in the lab you might get results that match your results.
However in the real world set your rifle to your desired range I use 37 yds for both calibres, then shoot a target at 45 50 55 and 60yd. Aim for the bull each shot and measure the drop with the mildots marked on YOUR SCOPE. Remember these and your sorted.
mk2 rapid.22
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