[Lasre]

I am not sure if this is the ideal forum but I could not see a beetter one.
Does anyone know of a ballistics program that models trajectorries of 44 240gn & 300gn WFN bullets when driven at 1030fps. This is a awkward speed as close to the speed of sound the BC tend to change in value very rapidly with a very small change in projectile speed. I would like to model the trajectory out to 150 metres at least. I currently shoot rabbits out to 170+metres with a silenced 22Lr (silencers use is actively encouraged in NZ). I would like to try out the 44 to a similar distance on goats and rabbits initially (there are more rabbits thsan goats to practice on).

Cheers,
Craig.

 

[IDShooter]

Craig,
You could use the External ballistics program here on the Beartooth site if you know the published BC of your bullets. If the BC is not known, you can calculate it if you have access to a chronograph and accurately measured shooting distances. There is a BC calculator on the site also; the addy is http://www.beartoothbullets.com/rescources/index.htm .

Hopefully someone will know the BC's of the bullets you are using and jump in! Unfortunately, I do not. Good luck and good shooting!

 

[MikeG]

I'd suggest starting out with a BC of .2 and work up some tables with the ballistics calculator. Then get out and do a little shooting to verify.

A BC isn't a hard and fast number, every gun varies a little plus you have things like altitude, temperature, and humidity which can all affect the drag on the bullet.

So.... even with the most careful calculations, you will still have to verify in the field. But I bet that you can get quite close with some estimates.

The Sierra manual shows a breakdown in the B/C over the supersonic and subsonic ranges, I think. Will have to check when I get home.

 

[Jack Monteith]

Hi, Craig:
Federal's CastCores have the only published WFN ballistics I've seen. They're on page 15 of this PDF.
http://www.federalcartridge.com/pdf/2003Fedcat.pdf

The BC looks like it's around .215. It's jumps around at each range but that's likely from rounding off to the nearest 10 fps. Besides, quoting BCs to 3 decimal places gets you paper precision that's unobtainable in the field. Sierra's numbers show a drop in BC below 900 fps for comparable bullets. However my home brewed Ballistics program only shows a difference of 0.9" at 200 yards with a 100 yard zero, using BCs of .220 and .190.

So far as I know only the Sierra and Oehler programs allow a variable BC.
http://www.sierrabullets.com/
http://www.oehler-research.com/explore.html

You should check out the calculator that IDShooter mentioned, as it's very precise, much better than mine. However, unless you can find accurate BCs for your bullets, a range test of drop is the best answer.

Bye
Jack

 

[kciH]

Lasre,
The RCBS Load program aslo can accomodate step BC's, but since I own it, I can tell you there are better programs for the money.

The best way for you to get a semi-accurate BC for your bullets will be to shoot them through a chronograph at varying distances from the muzzle of your weapon. I would only do this at extended ranges if I where shooting a scoped accurate handgun of a good rest and had not ben drinink any caffiene on that particular day....skyscreens can get expensive. This entire operation would depend on PRECISE yardage measurements ans shooting to be succesfull. The shooting would best be accomplished in as short of period time, on the same day, as possible to help minimize your error for temperature and atmospheric pressure, wind, etc, etc. You would also want to start with a load that you know has an extremely low SD or the attained data would be questionable.

 

[Lasre]

Thanks guys, I have Arthur Pejsa's & Quicktarget. I will try working out the bc based on the figures given for muzzle velocity and 100yd velocity in Federals catalog. The point I was getting at is that from the Sierra manual at 900fps the bc on a 240gn 44 JHC is 0.17 by 1050fps it has increased to 0.24 by 1100fps it is back down to 0.17 and from 1200fps up it has settled down to 0.18 I have used both to model 22Lr out to 220 metres and the curve does not follow the actual curve it is close but it is in error both up and down at various ranges. What is quite interesting is that we have to alter our holdover during the day less at the hottest part and more at dusk it is upto 1/2 a mil at times at 150metres.

Regards,
Craig.