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Discussion Starter #1 (Edited)
OK Math Wizards: here's one for you.

I like using the BTB External Ballistics Calculator in the Ballisticians Corner of this website.

It probably doesn't make a heck of a lot of difference for the short distances I shoot, but does anyone have a list of the Ballistic Coefficients for Beartooth Bullets? I am shooting 265 grain 44WFN and am entering a BC of 0.20 for that bullet.

What about the Drag Function? I just use the default G1, whatever that means.

If the BC and the DF are constant for each BTB, perhaps one of you Math Wizards can make a list for BTB to post on the site.

Thanks,
Dave
 

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Hi, Dave:
The only published BC I've seen for WFN bullets is Federal's, as discussed in this post, and I've looked.
http://www.shootersforum.com/showthread.php?s=&threadid=5781

Since Federal is rating their 300 .44 WFN at .215, I'd say .20 is a good guess for your 265 grainer. Right now I'm playing with the Lyman 358664 cowboy FN and using .15 as a guess.

You can be sure that every BTB bullet has a different BC. The BC equals sectional density over shape. Shape is called the form factor and is usually i in the equation, so BC or C = SD / i. So every time we change weight or diameter, we change SD, and if we change shape, say from a WFN to a LFN, we change i. To add to the fun, Sierra found that changing size can change i, even though the bullet is scaled up or down exactly. There are formulas for calculating the BC of typical high-power jacketed bullets, but the grease grooves in cast bullets throw in an extra curve. Lyman found that some pointed cast bullets had lower BCs than similar but blunter bullets. The theory is that the blunt point throws the shock wave away from the grease grooves, but the sharp point doesn't, and allows the grease grooves to create extra drag.

Most bullet manufacturers use the G1 drag function, and the few that don't say so. IIRC, Berger uses the G7 curve for his VLD bullets. This is sensible, as the G1 is a poor fit for VLD bullets that are used at a 1000 yards. Errors at that range are serious.

The BCs of the different drag functions are different, so your plain vanilla 30 calibre 180 grain spizter has a G1 BC of about .4, but it could be .2 or .8 in another drag function. Ingalls (GI) and G1 are close enough for most users to interchange. For more check out this short article.
http://www.shootingsoftware.com/ftp/bctech.txt

Bye
Jack
 

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Discussion Starter #3
I've hit the wall.

Thank you, Jack. I just wanted to know and I do appreciate your reply. I failed nearly every math course I ever took in school, but I can use a framing square and calculate the volume for storage tanks and other stuff I need to get done.

I have been doing pretty well and having a lot of fun with a lot of the numbers and measurements in this shooting and handloading game. However, I believe I have now reached my limit. I have hit the wall. :)

I have thought about some of those things, including the changing BC when things are scaled up. I guess that falls under the laws of physics.!? I know from building boats that scaled-up displacement hulls will go faster than shorter ones of the same dimensions (don't ever expect to outrun an aircraft carrier with your racing canoe.) I bet a different law of physics applies to scaling up bullets, but there could be some parallel there. I will read the columns you suggest, then go happily back to the reloading bench and keep doing what I am doing. This is a great hobby!!

Sincerely, Dave
 

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Greenhorn,
If you REALLY want to know what the BC is, you could get a Oehler M43 Personal Ballistics Laboratory. Bad news is it would cost you about $1050 for the unit and the parts needed for checking velocity at the standard distance plus 100yds from that distance. Oops, I forgot that you'd need a loptop to take to the range to hook it to also. The added benefit is that this unit will also help to determine safe chamber pressure for reloads. I really want one, but I can't quite justify it as of yet.

One means of getting it close, if you have a weapon accurate enough to give reliable results, would be to fire groups at 50 yds dead on with a scope and then fire the same groups 100 yds with the same scope and the amount of drop could be taken into account along with the height of the scope above the bore and you could fiddle with exterior ballistics programs until you found a close match. This would be a lot of fiddling around.

I know this doesn't satisfy your scientific side, but the most useful time you could probably spend on this project would be to take the gun out and shoot it at variable distances, since this is the only truly reliable means for determining where the bullets going to be anyway.

HERE is a link, if you're curious, or a fanatic with deep pockets.
 

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Discussion Starter #5 (Edited)
KciH -

Amazing!! I had no idea. I did check the Oehler link you put in your post. $1000 PLUS a laptop is a lot of $$$$, but I guess it is cheaper than renting a mathematician every time you go shooting.

I am not that extreme. My favorite gun is a short barrel 44 with open sights and I shot a full power 5 inch 30-shot group at 50 yards last month and I was so happy I think my smile stretched back to my ears. I know it impressed the guys next to me chipping away the target posts (like I did in the beginning) with their .22s @ 15 yards. Ah, the satisfaction of sticking with something until you get pretty good at it.

That said, I am way far from being good enough to need one of those Oehlers. As to safe pressures, I am still naive enough to believe the powder manufacturers max load recommendations.

I think I've pretty well decided that rather than buy more equipment, I'll just buy more powder and bullets and try to go shooting more often.

Dave
 

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Wise choice, Dave. $1000 can buy a lot of powder and boolets!:cool:

Stroman
 

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Discussion Starter #8 (Edited)
Since it is generally agreed that the 265 grain WFN Beartooth Bullet would be about .20, and the Sierra info states a range between .195 and .230 for the velocities at which I send those bullets downrange, I went to Beartooth's online External Ballistics program and ran 3 sets of numbers.

For all three sets I used the 265 grain weight, 1200 fps, left the G1 set where it is, used my open sight height of .85, set the temperatures etc at moderate, and entered a 60 yard zero which provides the best rise-and-fall average for the less-than-100 yards range I shoot in.

The only change in the three calculations was using .195 BC for one and .230 BC for the other and .5 BC for the third.

At 100 yards, which is near the end of the world for my skills, the .195 had dropped only .1 -- that's one-tenth of an inch -- lower than the .230 BC model. I can live with inaccuracies like that.

To push the envelope, I did a third try with the BC set at .5 and discovered only a .5 inch (half-inch) spread between the .195 and the .5 BC drop. I can still live with that. Mole hills for a guy who would be delighted if I could shoot a 6 inch group with open sights at 100 yards.

That said, when I get better I should pay attention to the BC. At an XKD (eXtreme Keith Distance) of 600 yards, the .195 would be thirty inches lower than the .230. The difference between the .195 and the .5 was 60 inches. So, if you are dealing in cannon-miles of distance you had better know what the BC is.

And now that I know all that, I can sleep better at night -- until the next question that puts me on the internet at wierd hours -- and I'll just go back to pouring the powder and pulling the trigger as I like to do.

Dave
 

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The Hog Whisperer (Administrator)
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Dave - you've cracked the code. For open-sighted handguns at any 'normal' range, the BC literally doesn't matter.

If I want to do a little thinking about trajectories, I just get my Sierra manual, and find one of their bullets that's close to the same weight, shape, and diameter, and use their B.C. numbers.

At 200 or 300 yards and beyond, hold-over is measured in feet... and plenty of them! At that range it's fun to just forget about B.C. and trajectories and walk shots into the target (assuming it's safe to do so).
 
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