# Thread: .204 ballistic calculation without chrony

1. ## .204 ballistic calculation without chrony

Is it possible to calculate velocity(approximately)by load data alone?
I'm thinking of buying the Swarovski Personalised Ballistic Cam for a .204 Ruger(have one for my .222 and like it),but don't have a chrony.
I'm using 32gr Blitzkings with 24gr of Vit N130 out of a 20 inch barrel. Would say 100fps difference make a big difference on bullet drop at 400yds? Thanks

2. Big difference? If you're shooting Volkswagons? No. If you're head shooting field mice?? Yes!
You have two things working against you: One is the lack of an exact velocity. The next is the lack of a precise ballistic coefficient for your particular environmental state where you live. The 32gr bullets haven't the best BC and pressure and altitude and humidity all have a bearing on the ballistics and especially at the tail end of it's working range. Your best bet is to take the manufacturer's BC as gospel, or take Vhit's veloicuty readings and do ethe same, then plug them into a ballistic calculator and generate a data sheet. Zero at 100 and shoot at 400. See how close the drop data is. If there is an error, pick which variable you want to believe it is, shrug your shoulders, make note of the actual amount of drop, and keep shooting. When you are done, go home and dink with the ballistic program changing what ever variable you believe is responsible for the difference in predicted drop, and actual drop. If you choose velocity, reduce/increase speed value in the program until it matches the actual drop you got. Now you know what velocity you are getting...or at least have a 'best guess' scenario that works for your particular load and generated data sheet. If you choose to believe Vhit's velocity data, then you juggle the BC until the data matches. You can choose which of the two you anchor to as the basis for your data.

In the end, only field shooting will tell you how much drop, drift, etc you are getting. You can't do it from home, and even the best data will let you down when the weather changes. (Unless you have some pricey ballistic gear handy which STILL requires accurate input) Only experience and your DOPE will be of real value. JMHO~Muir

(get a chronograph that will allow you to calculate actual BC and you will be on the road to nirvana)

3. Most ballistic apps have a velocity truing function (strelok+ that I use does) whereby you put in you guessed velocity and zero at 100m etc. You then shoot at 300m and dial in the amount of clicks it suggests. Take the shot and then correct the clicks until you're where you're supposed to be. Using the truing function then you put in this new number of clicks and it will tell you your velocity assuming (like Muir says) that your BC data is correct.

4. Thank you Muir and Nun Hunter. Head shooting field mice is definitely where I'd like end up,Muir,I'll start with rabbits and see where it goes from there. ��
sounds as though it would be a good idea to get hold of a chrony and assuming the manufacturer's claimed BC is correct all should be straightforward. Most of my shooting is done between 50-100m from sea level and temp range here is usually between 5-15 degrees C,so fairly stable there,the wind and myself are extremely variable,though,so the field mice are fairly safe,for now. Thanks again. W

5. I wouldn't worry about the chrony. Your end goal is to get actual drop values for your rifle for a particular load at an average temperature.
Having a chrony doesn't get you that with any confidence. 5 shot groups at 100,200,300,400 yards would be my approach. So forget velocity, BC, load data, etc, and simply order a custom turret that corresponds to where the bullet genuinely goes. It's easy to get tangled up in lots of great technical stuff, but I think it's a distraction in your case...

6. Originally Posted by simonl
I wouldn't worry about the chrony. Your end goal is to get actual drop values for your rifle for a particular load at an average temperature.
Having a chrony doesn't get you that with any confidence. 5 shot groups at 100,200,300,400 yards would be my approach. So forget velocity, BC, load data, etc, and simply order a custom turret that corresponds to where the bullet genuinely goes. It's easy to get tangled up in lots of great technical stuff, but I think it's a distraction in your case...
With the utmost respect Simon I don't think you should dismiss the chronograph as being a 'distraction'. In my book, without a chronograph to measure ES and the important SD and some one reloading ammo with a 100 fps spread and SD of 40+ then a drop chart calculation at extended ranges (400 yds+) would give quite a variation of POI. OK as Muir says for a Volkswagon but use a scrap one just in case you hit it.

7. Woodlander, the Sierra 55grn Blitzking i use in both my 223 @3360fps and my 22BR @3480fps drops 10" more with the 223 at 500yds

Ian.

8. Originally Posted by Whitebeard
Woodlander, the Sierra 55grn Blitzking i use in both my 223 @3360fps and my 22BR @3480fps drops 10" more with the 223 at 500yds

Ian.
What rifle?? (twist?) ~Muir

9. Originally Posted by PeterH
With the utmost respect Simon I don't think you should dismiss the chronograph as being a 'distraction'. In my book, without a chronograph to measure ES and the important SD and some one reloading ammo with a 100 fps spread and SD of 40+ then a drop chart calculation at extended ranges (400 yds+) would give quite a variation of POI. OK as Muir says for a Volkswagon but use a scrap one just in case you hit it.
I see your point, and agree with your facts, but not in this context...my interpretation was that woodlander was asking for a feel of what speed to put into swarovski's algorithm, and wanted a feel for how much difference 100fps might make. Even if I had oodles of speed results captured I wouldn't rely on calculated trajectory plots for specifying an expensive custom turret. I might get data with a chrono, in fact I've just bought one, but I would pay more heed to the empirical evidence, the more the better. If the swaro app says it should be a 20 inch drop at x yards and you consistently get 22 then what do you do? Either aim 2 inches high because that's what the computers say, or get the turret made to match where the bullets go?
I would change any old variable in the swaro app ... Velocity, BC, calibre, whatever to get as close as possible to real world drop. Most people preferring that turret typically don't want to bother with BC, moa, strelok, shooter, ES, SD mbar, temp.
Once the trajectory is printed on the turret the variables use to create it are never used again..

10. Originally Posted by simonl
Once the trajectory is printed on the turret the variables use to create it are never used again..
And the weather changes or you move, or are invited to shoot at lower or higher altitude. Then what happens to the turret? I live and shoot at an altitude pretty much equal to England's highest elevation. If a SD member from England came out to my locale on a hunt they might find such a turret less than useful. ~Muir

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