Ballistics Question

[erk444]

Ok, this might be long winded, but here goes. I shoot Barnes 290gr. TMZs. I'm out and I cant find any right now so I bought some 250gr. I went shooting today and they shoot great so I figured they will work fine for late season cause I'm only hunting deer. Now, according to the Barnes ballistic chart, My muzzle velocity should be around 1,952 fps with the 250 gr. and 1,808 fps with the 290gr. I know these are not exact due to the fact that I'm shooting a different muzzy then the one they tested with, but I figured the difference between the fps of the two weights should be pretty much the same. If I figured everything right, my kinetic energy should be around 2115 for the 250s and 2105 for the 290s. I may have figured wrong cause I thought I would have more KE with the heavier bullet? If not, then should I hunt elk with the 250gr. too, or will the KE fall off quickly once the bullet travels farther from the barrel? I just used a method off of the internet on a muzzy site to get my KE.
FPSxFPS/7,000/64.32xbullet weight=foot-pounds
Is that even right?

[Stein]

Energy varies with the square of velocity but linearly with mass.  Either one should have no problem making an elk dead in my book.

[Bob33]

Your calculations are correct.

"I thought I would have more KE with the heavier bullet? " Kinetic energy is combination of weight, and velocity. A 1000 grain bullet at rest has zero kinetic energy.

"will the KE fall off quickly once the bullet travels farther from the barrel?" That depends on the ballistic coefficient of each bullet. If they have the same ballistic coefficients they will lose energy at the same rate.

I think either would work fine. 

If I had to decide I would choose the one that is more accurate. If everything else is equal I would choose the heavier bullet. Everything else is rarely equal.

[erk444]

OK Bob, now I'm curious. How do I figure out the difference of ballistics coefficients between the two? Is there a way?

[Stein]

OK Bob, now I'm curious. How do I figure out the difference of ballistics coefficients between the two? Is there a way?

http://www.barnesbullets.com/products/components/muzzleloader/spit-fire-tmz/

Barnes lists BCs for both bullets, .241 and .210.

[erk444]

Thanks for the link Stein So the 290 has the higher BC at 241. Is the higher # better?

[Stein]

Higher BC = less drop for the same distance.  That said in a smokepole with open sights at smokepole distances the difference would be next to nothing.

[erk444]

I figured the difference wouldn't matter to much either. I think I'll just stick to the 290s. They haven't let me down yet. I've recovered only two from elk and none from deer. The two I found expanded perfectly. If it ain't broke, don't fix it right Thanks for the help guys, that's why I love this site

[bobcat]

I would never go as light as 250 grains for a muzzleloader bullet meant for hunting elk, EXCEPT for a Barnes or other 100% copper bullets.

With the Barnes, I think the 250 or 290 will work equally well on elk, but I would always choose the heavier one as long as the accuracy was there.

As for foot pounds of energy and ballistic coefficients, I wouldn't worry about the numbers at all, because that's all they are- numbers.