Bekker Knock Out Value and heavy slow bullets

[Dogger]

Fascinating discourse on the Bekker Knock Out Value at this website:

http://www.sportingrifles.com/knock_out_value.htm

What I find fascinating is the high BKOV scores for some cartridges most people don't get fascinated about. We Americans tend to drool all over velocity and energy figures. Maybe we are missing something. We tend to forget that higher (momentum) x (sectional density) equates to a deep penetrating, butt-kicking round.

As a baseline, the BKOV for a 30-06, 150 grain, 2910 fps cartridge is 14.1

The 6.5x55 Swede, 140 grainer, plodding along at 2550 fps scores a BKOV of 14.6!

My 7x57 Mauser, 175 grainer at 2440 fps scores a BKOV of 18.9. A 30-06, 180 grainer, clocking at 2700 fps scores an 18.8.

Again, the 7mm's high sectional density and good momentum carries the day.

The Swede's strength lies in its momentum and extremely high sectional density.

No wonder the Swede kills big critters -- it drives deep.

The 140 grain factory load in the new 260 Remington, moving out at 2750 fps, scores a BKOV of 15.8. Pretty impressive.

I really like the 220 grainer in the 30-06 though -- with a muzzle velocity of 2410 fps this combination scores a BKOV of 25.1.

For comparison purposes, a 375H&H 300 grainer at 2400 fps scores a BKOV of 31.3

So what does this mean to me? It means I don't have to beat myself to death with high velocity heavy recoiling cartridges. I just need to get in a little closer and make a well-placed shot. Well duh! No revelation here, I guess!

Sure makes me appreciate the fact that a good bullet, with high sectional density, impacting on the prey at say anywhere between 2200-2600 fps will kill cleanly and not damage a lot of meat.

Well, time to go get my checkbook and go find a 260 Remington! Then again, that 220 grainer in the 30-06 sounds like the perfect grizzly medicine for you Western hunters. I am afraid there ain't much in the Virginia deer woods begging for a 220 grain 30-06 round...

 

[Zak Smith]

Reduction ad absurdium.

.223 55gr at 3000: 3.7
.223 62gr at 2800: 4.4
.308 150gr at 2700: 12.6
.308 168gr at 2600: 15.8
8x57JS 150gr at 3000: 13.2
8x57JS 175gr at 2700: 16.2
.270w 100gr at 3400: 9.5 (from book)
.270w 130gr at 3100: 14.6 (from book)
.270w 150gr at 2900: 18.3 (from book)
.30-30 100gr at 2700: 5.8
.30-30 170gr at 2100: 13.1
.50BMG 750gr at 2800: 128.6
7mm-08 120gr at 3000: 10.9
7mm-08 162gr at 2700: 17.9
7mm-08 175gr at 2600: 20.1
6.5sw 129gr at 2700: 14.0
6.5sw 140gr at 2600: 15.9
6.5sw 160gr at 2400: 19.1
338lap 200gr at 3250: 23.2
338lap 225gr at 3000: 27.1
338lap 250gr at 2800: 31.3
416rig 400gr at 2400: 45.3

Smithz's BKOV running towards an elephant: 347

All the values from .270 down are from maximum load data in my Hornady and Speer books.

Another interesting exercise would be to evaluate these at the terminal velocities, as opposed to the near-muzzle velocities.

-z

 

[Dogger]

Terminal velocities...

Funny, I was thinking the same thing... great minds think alike! That is tomorrow's project... Where I hunt a long shot is 200 yards so that will be my baseline...

 

[Zak Smith]

My gut feel.

To calculate the terminal velocity, you need to cross-reference the muzzle velocity and B.C. at the range desired. This is a manual and tedious process for comparing many loads (not the least since you basically need to do it on a bullet-by-bullet basis, not just bullet mass). If I had a database of ballistic info, I could easily write a perl script to do so.

Anyway, my gut feel is that the terminal-velocity results will be nearly the same as the muzzle velocity results, merely scaled down a bit. I do not think the relative rank will change much because:

1. light and fast bullets already do poorly in BKOV
2. slower heavier bullets already do well in BKOV, and do not lose as much relative velocity
3. bullets with high sectional density generally have higher BC

-z

 

[Dogger]

I played around with BKOV at 200 yards and hardly anything moved out of place. As expected, the fatter rounds lose velocity faster, and so momentum drops, but all in all things remained pretty much the same.