Rebarrel to fast twist 270 Win or go 6.8 Western?

[Gorp2007]

Then explain the difference in velocity and energy to me between these two loads. And explain to everyone why you think the 129 would perform better than the 155 on elk at each incremental distance past 400 yards. Assume a shooter mistake and the bullets are both going to hit the elk in the scapula.

Sure thing, friend!

The velocity of the 129 will be higher, so it’ll do a better job of opening up at any distance where the velocity remains higher.

Energy only matters as a factor of velocity, so the comparison is irrelevant unless you’re using directed energy weapons.

Either one will punch through an elk scapula, so it’s as irrelevant as energy. Plenty of photographic evidence of bullets punching through elk shoulders if you bother to look around.

Good luck and let us know if you decide to do something interesting!

 

[bmart2622]

Velocity does dictate energy but so does bullet weight. They work in combination. The heavy high bc bullets hold velocity longer and with the weight also have more energy at range

And velocity dictates bullet expansion

 

[bmart2622]

Velocity x velocity x mass does not equal force. Change in velocity x mass = force (energy).

Do yourself a favor before you look even more foolish and put your foot even further in your mouth and google the calculation for finding a bullets ft/lbs of energy

 

[alpinewanderer]

Do yourself a favor before you look even more foolish and put your foot even further in your mouth and google the calculation for finding a bullets ft/lbs of energy

Okay. We both have our foots it our mouths because we are not being precise about our language here. If you are talking about energy, more properly kinetic energy, then the formula is 1/2V^2*m. That's half the square of the velocity times the mass. In damaging things with projectiles we are interested in the transfer of momentum from the bullet to the object. As you've shown yourself mass is also a component of energy. So if the velocity increases and the mass stays the same, you have an increase in energy. You can also increase the energy if the velocity is constant and you then increase the mass. Velocity doesn't kill elk and deer, the transfer of energy or more properly, transfer of momentum kills deer. I think people are interested in velocity because by increasing it you can get more energy using the same bullet weight. But a lighter bullet generally won't retain its momentum over a longer distances. Hence you can see that the 155 gr bullet above has more retained energy at 600 yards than the 129 gr bullet.

I don't know how, when looking at two projectiles of identical diameter and identical construction but different weights that one could think the projectile with less kinetic energy would transfer more of that energy to a target than one that has more. At 500 yards both a Barnes 129 gr. LRX and a 155 gr. LRX have the velocity to expand almost instantaneously but one has more KE than the other. If the bullets only touch skin and organs both would probably work fine. But if they touch dense and thick bone the one with more KE is more likely to break through and keep moving into the animal.

Shot placement and bullet design and construction have a lot to do with energy transfer but it seems like a lot of you guys are kind of stuck on velocity only. Shot placement, bullet construction, BC, SD, frontal diameter, bullet weight, and velocity all play a role. I said from the beginning that I'm using 129s right now and would like to shoot 155s fast enough to produce more KE than my max charge for the 129s. Based on the ballistic data from Barnes, I get all the ballistic benefits of the 129 gr. but with a 155 gr. AND I get more KE farther out with the 155. Both the 129 and 155 are traveling fast enough to almost instantaneously expand completely on impact at 500 yards.

Hence the interest in the faster twist 270 Win. Still nobody has had anything to say about the 6.8 Western which is the other chambering I am considering. I expect because none own or have used it.

 

[bmart2622]

Well since we are on Rokslide and this is in a Firearms section it would seem pretty self explanatory that we are talking about ft/lbs of energy acheived by a projectile, so, again, your foot is in your mouth. So how do you explain the dozens and dozens of animals killed, complete with necropsy photos on this website alone, caused by projectiles that fall below your Fudd Lore threshold of 1500ft/lbs of energy?

 

[fuzzymarindave]

Okay. We both have our foots it our mouths because we are not being precise about our language here. If you are talking about energy, more properly kinetic energy, then the formula is 1/2V^2*m. That's half the square of the velocity times the mass. In damaging things with projectiles we are interested in the transfer of momentum from the bullet to the object. As you've shown yourself mass is also a component of energy. So if the velocity increases and the mass stays the same, you have an increase in energy. You can also increase the energy if the velocity is constant and you then increase the mass. Velocity doesn't kill elk and deer, the transfer of energy or more properly, transfer of momentum kills deer. I think people are interested in velocity because by increasing it you can get more energy using the same bullet weight. But a lighter bullet generally won't retain its momentum over a longer distances. Hence you can see that the 155 gr bullet above has more retained energy at 600 yards than the 129 gr bullet.

I don't know how, when looking at two projectiles of identical diameter and identical construction but different weights that one could think the projectile with less kinetic energy would transfer more of that energy to a target than one that has more. At 500 yards both a Barnes 129 gr. LRX and a 155 gr. LRX have the velocity to expand almost instantaneously but one has more KE than the other. If the bullets only touch skin and organs both would probably work fine. But if they touch dense and thick bone the one with more KE is more likely to break through and keep moving into the animal.

Shot placement and bullet design and construction have a lot to do with energy transfer but it seems like a lot of you guys are kind of stuck on velocity only. Shot placement, bullet construction, BC, SD, frontal diameter, bullet weight, and velocity all play a role. I said from the beginning that I'm using 129s right now and would like to shoot 155s fast enough to produce more KE than my max charge for the 129s. Based on the ballistic data from Barnes, I get all the ballistic benefits of the 129 gr. but with a 155 gr. AND I get more KE farther out with the 155. Both the 129 and 155 are traveling fast enough to almost instantaneously expand completely on impact at 500 yards.

Hence the interest in the faster twist 270 Win. Still nobody has had anything to say about the 6.8 Western which is the other chambering I am considering. I expect because none own or have used it.

I’m big on velocity and would prefer both entry and exit holes over dumping all bullet energy into animal. I shoot 6.8 Western and it was pointed out that the case rim is too large for your bolt face. Just get a fast twist .270 Win or try a rebated rim cartridge if you want more velocity. 270-284 Win was mentioned. Or maybe be the first with a 6.8- 6.5 Weatherby RPM.

 

[alpinewanderer]

I built a fast twist .270 with a long throat usually load just under 3.6. everyone says don't do .277 for bullet choice but I've found if you shoot monos (I live in California) that is absolutely not true and every nonlead manufacturer has good options for heavy .277.
Right now I'm shooting badlands bulldozer 140s at 2950 which keeps me above 2k out past 1k with low recoil though that's way past my comfortable range

Wow.

 

[alpinewanderer]

Well since we are on Rokslide and this is in a Firearms section it would seem pretty self explanatory that we are talking about ft/lbs of energy acheived by a projectile, so, again, your foot is in your mouth. So how do you explain the dozens and dozens of animals killed, complete with necropsy photos on this website alone, caused by projectiles that fall below your Fudd Lore threshold of 1500ft/lbs of energy?

Dude, I've killed animals with a weapon with an order of magnitude less KE than 1500 ft-lbs. It's my compound bow. But that 514 gr arrow and broadhead combo are also probably an order of magnitude less forgiving. KE buys forgiveness. The bow and arrow allow for a very narrow window of shot angles, vital hit options, and distances, compared to a centerfire rifle. I've killed 13 big game animals up to and including elk with .270 win mono metal bullets and kept my shots close enough to meet that KE threshold. 12/13 were one shot kills. I've really liked that track record. Maybe your right, maybe I'm being too conservative and monos and just way more powerful with the penetration abilities for me to worry about shooting farther than 400 with a 129 gr.

But things go wrong man. If you hunt you know. During one of those shots a longer one (~400 yards I think it was) the elk must have moved its leg or I jerked the shot and the bullet went crashing through the front leg. It killed the animal right there but it absolutely wrecked the meat of the front right quarter with clotted blood and bone fragments and didn't get much from it. So I wonder what could have happened if I took that shot from 200 farther away. Could it have been a wounding?

So why come into this thread with hostility and a mocking tone? I never said you were an immoral guy if you shoot animals when your bullet has less juice than 1500 ft lbs. I'm saying I just don't want to.

And what I really want are helpful insights into 1:7.5 .270 Win vs. 6.8 Western, which you never gave.

 

[alpinewanderer]

I’m big on velocity and would prefer both entry and exit holes over dumping all bullet energy into animal. I shoot 6.8 Western and it was pointed out that the case rim is too large for your bolt face. Just get a fast twist .270 Win or try a rebated rim cartridge if you want more velocity. 270-284 Win was mentioned. Or maybe be the first with a 6.8- 6.5 Weatherby RPM.

I can always just get a magnum bolt for the tikka. Let's not consider that a factor. Do you still think the fast twist 270 Win would be a better choice than the 6.8 W?

 

[Koda_]

And what I really want are helpful insights into 1:7.5 .270 Win vs. 6.8 Western

The "performance" section of the Wikipedia article of the 6.8 Western directly compares its ballistics to the standard 270 (If I read correctly comparing a 150gn bullet respectively...). Note: the 6.8 uses a fairly fast 8 twist barrel by its design to stabilize heavier ie higher BC bullets, 165-175gn.
I think if you want to compare the two calibers head to head, the 6.8 "wins" by the numbers only but if you wanted to breath some life into the equally qualified 270 improving it with a modern chamber and fast 7 twist will give you options that are virtually equal to the 6.8.
I think.. IMO, if you suped up your 270 it would be worth it to go with an Ackley Improved chamber as well to maximise its potential with the heavier higher BC bullets.

At the end of the day comparing calibers your splitting hairs here, your two contenders are more than enough as is for any big game in North America... except you've lamented the sentimental value of your beloved 270 and to me that has merit. You have memories with it, enjoy it, it sounds like what you shoot best. The barrel/chamber upgrades to it will not hinder shooting traditional bullets or loads in the 270, especially with monolithics that cant be overspun. Recently, the advantages of faster twist rates were shared in a post by Bryan Litz I think would be of interest to you, in short its an advantage. The fast twist 270 guy above validates that, as youve noted impressive results already.

My vote is for your 270 with a 7 twist and throated long will give you a traditional caliber that hits way above its class with the modern 6.8...

https://www.facebook.com/BryanLitzBallistics/posts/pfbid0tTVTNnsEP8PFDYGkY9wtVvYkWgNQo8kyXSbxn9TiD2CT1wpNsv6ugmSU1u6SbN87l