Developing drop charts?

[wisconsinteacher]

I know that the best way to do it is to hit the range and test things, but I would like to make a chart for my 22-250 and 6.5 Grendel.

Do I have enough info?

22-250
Ave FPS-3519
SD-21.9
Number of shots tested-9

6.5 Grendel
Ave FPS-2302
SD-12.46
Number of shots tested-9

 

[Mud]

What bullet are you using?

 

[wisconsinteacher]

55 Vmax for the 22-250 and a 107 gr Sierra MatchKing for the 6.5

 

[Songdog]

Zero distance?
Scope height?
Avg. altitude (or barometric pressure) you shoot/hunt at?

 

[Mud]

Here you go. I hope this helps. I use a ballistic app on my iPhone.

Larry

 

[.300winmag]

Zero distance?
Scope height?
Avg. altitude (or barometric pressure) you shoot/hunt at?

Temp you wish your drop chart for and chronograph distance would be useful as well. I've got an excel spread sheet made up that is linked to my ballistic program (Point Mass by Bryan Litz) I used to run my drops for me and my buddies and laminate them for us to use while hunting and in tactical matches before the smart phone apps were available. If you would like, I can run numbers and you could verify them then I would be more than happy to mail you verified laminated drop cards if you do not wish to buy an app.

 

[wisconsinteacher]

Thanks for all the help. I guess my question was not how to make a chart but, do I have enough info to develop one after only shooting 9 shots?

 

[wildgene]

...plenty of data to start w/, try any one of the ballistics computers available, then "Truth" your loads @ distances. There's no substitute for checking your actual drop @ ranges & comparing to the estimated drop of your ballistics table. I emphasize "estimated" here because B.C. is a complicated equation w/ a bunch of variables w/ varying degrees of effect on your actual ballistics, TOF (time of flight) being one of the most important. As your distance increases the effect of the variables increases. Putting good info into a good ballistics program should get you on paper, but checking your actual bullet drops @ ranges is the only way to know what it's really doing...

 

[Songdog]

Thanks for all the help. I guess my question was not how to make a chart but, do I have enough info to develop one after only shooting 9 shots?

Yes.... and no.

You have enough information to make a preliminary chart. After that, it'll take a lot of shooting to VERIFY said chart....

Here's a well worn drop chart for my 7RM Sendero running 162 Amax at 3100. As you can see... it has been around a while, and verified to around 1200yds.

You only need a couple rounds to speculate.... but it takes a couple hundred rounds to KNOW.

PS... well said Gene.... you must type faster than me...

 

[FOTIS]

Way to go fellas. Good stuff here!

 

[AzDak42]

...plenty of data to start w/, try any one of the ballistics computers available, then "Truth" your loads @ distances. There's no substitute for checking your actual drop @ ranges & comparing to the estimated drop of your ballistics table.

Spot on.

All I'd add is the note that the ballistic software all uses models that are based on your bullets BC. It's important to know that their are multiple different models/ways of measuring your BC. BC also isn't a perfect measure.. How efficiently your bullet cuts through the air at 3000fps may not equal what it does at 2400fps. Two bullets of the same BC, may behave differently at different velocities. Complicated enough yet?

So what we get is something that is a pretty darn good starting spot. I've generally found that any errors in the model are pretty trivial up close, say inside 300 yards, but you start seeing some cumulative error creeping in the further out you shoot. Your correction at 1000 is a more than your correction at 400. (At least on the two rifles I've taken out that far...)

To put it in perspective, bullet drop charts are what you use to get close. Actually using the rifle and load at a known distance course, will get you the exact, repeatable data.

 

[Mud]

Like the above posts. Now comes the fun part. Verifying the drop table. But keep in mind altitude, Baro pressure, temp and ect. will shift your point of impact. The tables I provided are defaulted to sea level. If you want pm me your email and I can send you the drop tables on picture format,

Best,

Larry

 

[ScreaminEagle]

What you need to do is get on Vortex Optics website, and use their LRBC system. It is hands down the most accurate calculator i have used. You will still have to test it out with real worls conditions, but it will get you VERY close!
Steve

 

[usmc 89]

Kestrel 4500 with the horus ballistics, this will give you current information to apply to your scope regardless of changing conditions assuming your initial inputs are accurate.

 

[hundmeister]

Hornady website I believe has a ballistics chart to print off. basic and advanced. Give it a try.

 

[Oldtrader3]

To attain a decently repeatable "s" for each of these loads, you will need to shoot at least 30 rounds for each load to assure a 90% probability (check tables) of velocity data repetition. Just my $.02. Having "degrees of freedom" issues with your data because of too few samples puts all your results at risk.