Selected Caliber Comparisons - Retained Kinetic Energy
I recently read a Military Times article by Todd South about Special Operations Command looking into using a 6.5mm round for bolt action sniper rifles. Two commercially available rounds being evaluated are the .260 Remington and the 6.5mm Creedmoor.
This got my attention because I have for some time wanted to build a custom bolt action rifle like my father used to do. I was thinking in terms of a flat shooting long range rifle and had settled on .25-06 for the caliber. In terms of bullet diameter the .25-06 and 6.5mm are very close, .257 inches for the .25-06 and .264 for the 6.5mm. After perusing the internet and reading several articles comparing the 6.5 Creedmoor, .25-06, and .260 Remington, I had the impression the 6.5 Creedmoor might be a better choice for my custom gun. I was curious to know how they compared with regard to energy retention at longer ranges, so I got out my Hornady reloading manual, cranked up Excel, and put together a spreadsheet.
Initially I was only comparing the .25-06 and 6.5 CM, but then I wondered how they would compare to a couple of standard military rounds, the 5.56mm NATO and the 7.62mm NATO. And then, just for fun, I wanted to see how they all compared to my personal long time favorite cartridge, the .45-70, and another flat shooting long range cartridge, the .22.250.
My process began with looking at the Hornady reloading manual for each caliber, choosing hunting bullets, not competition bullets. Since I wanted to know about energy retention at long ranges, I chose the heaviest bullets, knowing their long range performance would be better than lighter bullets. For each bullet/cartridge combination I noted the bullet weight, the ballistic coefficient of the bullet, and the maximum muzzle velocity the bullet could be driven to.
I ended up evaluating 25 bullet/cartridge combinations:
Two 5.56 bullets weighing 60 and 70 grains
One .22-250 bullet at 60 grains
Seven .25-06 bullets ranging from 75 to 120 grains
Six 6.5mm CM bullets ranging from 95 to 160 grains
Five 7.62 bullets ranging from 125 to 190 grains
Four .45-70 bullets ranging from 300 to 500 grains
For each bullet/cartridge combination I fed the bullet weight, ballistic coefficient, and muzzle velocity into Hornady's online Standard Ballistics Calculator (http://www.hornady.com/ballistics-resource/ballistics-calculator) and determined the kinetic energy in foot-pounds at the muzzle and at 100 yard intervals out to 1000 yards.
With all the energy values loaded into the spreadsheet, for each range from muzzle to 1000 yards I ranked each bullet/cartridge combination from highest to lowest kinetic energy, giving the highest performer a 1, the second highest a 2, and so on. After ranking all the bullet cartridge combinations, I added up all the ranking scores for each one, to get an overall ranking. After sorting by that overall ranking, I used colors to denote the top 6 performers, gold, silver and bronze for the top three, followed by blue, green, and beige.
The results were interesting. I was not surprised that at closer ranges the .45-70 shooting a 500 grain Hornady DGS rules. One small surprise was the top performer at the muzzle was the 350 grain Hornady InterLock FP. But the low ballistic coefficient of that bullet dropped it to 3rd place at 100 yards and down to 11th or lower after that. The 500 grain retained the most kinetic energy at 100, 200, and 300 yards, and for 700 yards and beyond.
The overall second place bullet was the 180 grain Hornady SST with a muzzle velocity of 2500 fps (feet per second) in the 7.62 NATO cartridge. This bullet had the most retained energy at 400 yards, and was in the top three from 300 to 800 yards.
Third place is where it gets interesting. The 140 grain Hornady SST comes out of the 6.5 Creedmoor with a muzzle velocity of 2725 fps. Between the muzzle and 200 yards this bullet isn't even in the top six energy-wise. But from 400 yards on, this bullet is either second place or better; at 500 and 600 yards it retains more energy than any of the bullet/cartridge combinations I evaluated. This bullet also has the highest ballistic coefficient of any I looked at, 0.520.
When I changed my overall ranking to only consider results 300 yards and further, the 140 grain SST in 6.5 Creedmoor had the best overall energy retention. At 700 yards and greater, the only bullet to retain more energy was the 500 grain .45-70.
When looking at the practicality of long range shooting, in spite of the greater energy retention the .45-70 has a distinct disadvantage, trajectory. When zeroed at 200 yards, the bullet drop at 1000 yards is 96 feet (32.2 mils)!
The 140 grain 6.5mm CM bullet has a 1000 yard drop of 28 feet or 9.4 mils. So, flatter shooting than the .45-70 and 7.62 NATO, and from 500 yards on more energy than the 7.62 NATO. I like it.
How did the other three cartridges compare? The 22 calibers (5.56 NATO and .22-250) don't even come close with regard to kinetic energy, starting with the least energy at the muzzle and losing what they had quickly. And the .25-06? The best bullet I evaluated, the Hornady InterLock HP with BC of 0.394, at 3000 fps, was 9th or 10th best at any distance. I think it's main problem is lack of bullet selection in .257 from Hornady. It's possible some other manufacturer offers .257 diameter bullets in heavier weights and with better BC.
For me, the bottom line is, for anything 300 yards and closer, my tried and true .45-70s deliver the most energy to the target, but beyond that, I think I want a 6.5mm Creedmoor handy.
Oh, and one other note about the spreadsheet. I was curious how these long guns at long distances compared to standard handguns at point blank range. A typical 9mm load generates 300 ft-lb of energy at the muzzle, and a .44 Magnum about 900 ft-lbs. The cells outlined in black show the farthest range with energy of 300 ft-lbs or more. The cells outlined in red show the farthest range with energy of 900 ft-lbs or more. Just an interesting point of reference.