A good deal of research, scratching of the head and (gulp) prayer has enabled me to come up with a modified TE (Terminal Effect) formula that I think satisfies my personal belief that both kinetic energy (KE) and momentum are involved in the killing of game animals, or dangerous game, regardless of size or disposition. And the formula is more straight forward and simpler. It combines KE at impact (whether at 2 yards or 1000 yards) with a momentum factor (MF) that takes into account both sectional density (SD) and the cross-sectional-area (CSA) of the bullet prior to impact. Then the KEI is multiplied by the momentum factor (MF), divided by 100 for approximate game weight (GW) under normal conditions. Thus:
KEI x MF/100 = GW
For example: a 250gr impacts a moose at 2002 fps. KEI is 2002 squared/450400 x 250 = 2225 ft-lbs of KE (at impact). Next operation, in separate brackets, is a basic takeaway from the TKO formula with these simple distinctions: CSA replaces nominal caliber and SD is included, such as: 2002 fps x 250 x .101 (CSA of a .358 cal) x .279 (SD) = 14,103.6/300 = 47 MF.
Then as a stand alone formula: KEI x MF/100 = GW, as in the example below:
2225 ft lbs X 47 MF =104,575/100 = 1045 GW
So, dependant on cartridge used and bullet, 2002 fps will impact the moose at variable ranges. But let’s say the cartridge is a .35 Whelen firing a 250gr NP at a nominal 2600 fps. Bullet impact at 2002 fps (enough for expansion) would be all the way to 338 yards (under average ambient conditions for a moose hunt). Using my computer ballistic program (which allows inputs of temp., humidity and elevation), velocity at 338 yards would be 2002 fps or 2225 ft-lbs. That’s plenty for a big elk or bull moose if hit in the right place with the right bullet.
From this point onward (DV), I’ll be using this model to determine the appropriateness of a particular rifle load for my purposes If I don’t already know, or have some questions.
A further example could be my current “bear load” from the Ruger #1 in .458. How far could it be effective? And what about its trajectory? Since I’ll be “walking it up” in variable physical conditions, a shot could be conceivable at up to 300 yards across the end of a lake with a bear strolling on the other side. At what range would my modest load of about 2100 fps be acceptable for placing a shot into vitals? I have to check that out in using my computer ballistics program with inputs for temp, average humidity and elevation. I’m familiar with the average temps for September, October and November for that area, but still that’s a variable, and so is humidity but neither of those will dramatically affect POI on a bear. I just need to be aware of it. And elevation (which is the most significant factor) I already know. That’s a variable somewhere between 1000 to 1300 ft depending on exact location.
< And the Ruger in .458 needs a workout from time to time, and that’s not at the range! So also its owner!
Current MV of the 405gr Remington = 2085 fps; SD = .276; BC = .281
Zero is now dead on at 100 yards, but I’ll elevate that to about +3″ at 100 yds for information, just in case it’s needed.
Also, I know the bullet is a “killer” even if it doesn’t expand, or I could use the 400gr Barnes Buster in its place that is going a bit faster but has a poorer BC of .242. Whatever the case, the table below is of the 405 Rem at 2085 fps MV.
MV = 2085 fps = 3909 ft-lbs (zero at 170 yards)
50 = 1954 fps= 3433 ft-lbs (120 MF x 3433/100 = 4124 GW) +1.81″
100= 1828 fps = 3006 ft-lbs (112.4 MF x 3006/100 = 3378 GW) +2.92″
150= 1709 fps = 2625 ft-lbs (105 MF x 2625/100 = 2756 GW) +1.43″
200= 1595 fps = 2289 ft-lbs (98 MF x 2289/100 = 2245 GW) – This would be the approximate range limit on bear due to trajectory, but could be longer for larger game. Would the right 400gr/ .458″ bullet at about 1600 fps impact, in the right place, kill a 2200 lb soft-skinned animal? I’m sure it’s been done, especially with something like the Punch bullet. (Traj.-3.04″)
250= 1489 fps = 1993 ft-lbs (91.5 MF x 1993/100 = 1824 GW) -10.93″
300= 1390 fps = 1737 ft-lbs (85.5 MF x 1737/100 = 1485 GW) -22.75″. Is a hardcast 405gr at 1390 fps at impact sufficient for a 1500 lb soft-skinned animal if hit in the right place? There’s no doubt it has been done many times over! But if that were my intent for an eland, for example, I’d not be using the 405gr Remington but a more solidly constructed 400 – 405gr with a flat tip (FT). The point being that a well constructed 400 – 405gr at 1390 fps impact, at whatever the range might be, should be more than adequate for a soft-skinned 1500 lb animal if correctly placed.
My former formula gives about the same results (1737 ft-lbs x .276 (SD) x .165 (CSA) = 79.1 TE x 20 = 1582 GW with a broadside hit in the vitals.
Then there’s an excellent suggested formula by Dr. Ron Berry (“Riflecrank”) on the 24hrcampfire forum at the .458 Winchester Magnum thread.
But whatever I (we) use for estimates, it’s already been done long ago. And that was based on experience that came from trial and error in the use of both soft and solid projectiles.
At the very least, I’m satisfied that the potential ballistics of my “bear load” is plenty for any size bear at any range that practical trajectory permits, and within recoil that’s more than tolerable from my .458 Winchester Magnum. But for “any bear” up to and including grizzly, I’d not be using the .405 Remington due to its structure in hitting a large bone. So even now I’m having doubts about the potential size of a black bruin I could encounter. Over bait is one thing where waiting for a bear to turn broadside is always a possibility, and I’d have no doubts about the 405 Remington, but a surprise encounter with a really big bruin at close range is another. In such a scenario, angle of presentation isn’t an option. Ergo: In a “walking about” or calling scenario from any potential location, no doubt I’ll be loading the 400gr Barnes Buster at it’s current 2100 fps. So again, the selection of a particular projectile (soft or solid) should depend on potential circumstances and the animal pursued.
Because of limited time this year for bear hunting, due to other family activities, I’m not planning for a dedicated baiting season for bear. Instead, it will be scouting for bear, and some calling, in mixed terrain that I’m familiar with. And, as already noted, that could be inclusive of some more open areas where a potential shot could be taken across a meadow, small lake or clearing. A logging operation is currently ongoing in that area so I want to check that out as well. Also, how much assistance I may or may not have from a partner will be involved in taking a particular bear or not, as well as distance from my SUV. But, my main interest is “to get out there” for the adventure in toting my No.1 Ruger in .458 Winchester Magnum! If I just sit at home thinking about it… what good will that do?
With one in the chamber, plus five in a buttstock ammo holder, the rifle, plus the 2-7 x 32mm Nikon scope, weighs 10.6 lbs. With the Mag-na-ports, recoil is about 29 – 30 ft-lbs, and recoil velocity is about 17 fps. By the time bear season is finished at the middle of November, I’ll be within 6 weeks of my 86th birthday, and despite a severe bout of arthritis last winter, I’m not troubled in the least with the prospect of toting a 10.6 lb rifle and 30 ft-lbs of “kick”! But, truth be told… I’m not living from year to year but one day at a time. (See Jesus teaching about worrying over money, possessions and life: Matthew’s Gospel, chapter 6, verses 9 through 34.)
I truly want, whomever you might be, God’s very best for you, both now and on into the future, however that’s to be understood. (St Jame’s Epistle, chapter 1, verse 17: “Every good and perfect gift is from above, coming down from the Father of heavenly lights, who does not change like shifting shadows.” NIV)
Til next time which, as mentioned, might not be on schedule due to upcoming extra family activities. But if and when I do “get out there”, I’ll be sure to let you in on the action!