how do I figure elevation difference after sighting in with those other bullets

[rhill]

I have my .243 sighted in at 100yds with 80gr. jacketed loaded to 3200fps. I am going to try cast 90 grain at about 1650fps. How much elevation should I dial in to get impact close? Trial and error seems like a waste of time and ammo. Is there a formula to use to figure it out? Cast in .243 is new to me and the trajectory thing has me lost.:veryconfu

[MT Gianni]

No idea other than shoot but my old 243 shot 100 gr @ 2875 fps and 100 gr cast with 13 gr 2400. It was 38 clicks difference for a 100 yards with the jacketed shooting 3" high and the cast dead center. Put a piece of paper under the elevation adjustment cap of the scope as to what it is set for, don't trust your memory.

[rhill]

Thanks-that gives me a good place to start. I was just guessing but I figured it could be around a 10" difference.

[Blammer]

move the target to 25 yds to start, that will help you find where it hits, and help you with groups too. If it won't group at 25 yds you need to modify something. :)

[Toymaker]

There are enough ballistics calculators around than you can shake a stick at. Any one of them will help you. http://www.hornady.com/ballistics-resource/ballistics-calculator

Do start at 25 yards. It only takes one shot, one adjustment. Then move to 50. Two shots, two adjustments. Then work at 100 if that's where you want to be.

[prs]

The same way you test pudding.

prs

[country gent]

WIth no "starting point to work from with the load its hard to say where it will actually hit. Pressure, Harmonics, recoil all playa role in where a new load is going to hit. Once you have a starting point then ballistic calculators or drop charts can be used to determine come ups for range. Start close (25 or 50 yds) and zero quick 1 shot measure its distance out and figure corection a second round to verify. Then move back to longer ranges. The 243 is pretty mild mannered and should be pretty easy to get dialed in.

[s mac]

As said start at 25 yards. Besides, shooting, load development is part of the fun.

[popper]

Calculator will give you a general idea, BC & fps are prime factors, boolit weight is not. GeBC.exe downloaded from this site is good. Then like MTGianni says -write it down. You will have to shoot it to get the right answer.

[Love Life]

No idea other than shoot but my old 243 shot 100 gr @ 2875 fps and 100 gr cast with 13 gr 2400. It was 38 clicks difference for a 100 yards with the jacketed shooting 3" high and the cast dead center. Put a piece of paper under the elevation adjustment cap of the scope as to what it is set for, don't trust your memory.

Are your "Clicks" 1/4 MOA? So 9.5 inches or there abouts with MOA being 1.047 inch at 100 yds...

[W.R.Buchanan]

I have done this for several guns and no matter what the Ballistic Calculator or Drop Chart says you will still have to shoot it at all the different ranges you plan to shoot at to verify the results.

The two primary factors as mentioned above are Ballistic Coefficient of the boolit and the Velocity. In Lyman's Big Cast Boolit Handbook, 4th Edition, there are many pages in the back that have drop charts for all the boolits they are currently making moulds for. These charts have the BC of the boolit and then drop charts for many different velocities. If you don't have a chronograph then you can figure your boolit's speed using these charts. Once you know the speed for sure you can plug those into a Ballistic Calculator and define your trajectory more closely. However the drop charts are very accurate to begin with, and this is how it was done for 100 years before the Personal Computer or I Phone was invented.

You will still have to shoot the gun with your established load to verify your calculations. There is no other way.

Close is fine,,, but exact is better.

No Matter how precise your calculations are, there will always be unseen variables which will affect the boolits flight. Shooting the gun reveals the boolits flight path in the Real World and in the end that's what counts.

I highly recommend that you settle on a standard load for your gun that produces best accuracy or acceptable accuracy, using the boolit and powder of your choice,,,, FIRST!

Then work the trajectory.

This is because if you change anything about the load,,,, you get to start all over.[smilie=b:

Randy

[rhill]

All good info here, thanks! I was just wanting to get on paper quickly, but no big deal, I will just post a target at 25,50,75,100yds and get it dialed in, and record each adjustment so it won't be a mystery anymore. I can then chrono the load and as said then run the numbers in the computer to get the longer distance drop. At my gunclub we are installing steel gongs on a closed down portion of the range, shooting lead at these sounds like a real good time!