Rebarrel to fast twist 270 Win or go 6.8 Western?

[Lou270]

In a tikka LA if you can load longer than 3.34 in the magazine then regular 270 with fast twist is ok. Mainly because most of the high bc bullets made for .277 are built for 6.8W with more head height so you MAY run into situation where ogive of bullet is below case mouth if limited to 3.34. I don’t know off hand what the tikka oal limit is but other than that the main difference (if handload) is the 6.8W has a bit more case capacity (74ish vs 67ish grains) from performance standpoint.

As for bullet expansion, velocity does not expand bullets. Impact velocity makes a soft/liquid target “harder” than the bullet (dynamic pressure) such that the bullet deforms until slows down enough during penetration that the bullet is again “harder” than the target and stops deforming. This happens very early during penetration as the bullet slows down quickly once deforms. Energy is what deforms the bullet.

Lou

 

[Formidilosus]

As for bullet expansion, velocity does not expand bullets. Impact velocity makes a soft/liquid target “harder” than the bullet (dynamic pressure) such that the bullet deforms until slows down enough during penetration that the bullet is again “harder” than the target and stops deforming. This happens very early during penetration as the bullet slows down quickly once deforms. Energy is what deforms the bullet.

Lou

So how much ft-lbs of energy does it take to upset a Barnes bullet?

 

[Lou270]

So how much ft-lbs of energy does it take to upset a Barnes bullet?

How many fps does it take if you hit a rock

 

[Koda_]

Why do all the bullet manufacturers list their bullets expansion with velocity instead of energy?

 

[Formidilosus]

How many fps does it take if you hit a rock

What does a rock have to due with tissue.

 

[Lou270]

Why do all the bullet manufacturers list their bullets expansion with velocity instead of energy?

View attachment 771107

Think about it this way. It only takes a couple hundred ft-lbs for a bullet to deform (depends on a bunch of stuff). However a bullet is much more dense than flesh. A bullet needs to hit at a certain speed to make the target harder than the bullet so it will deform. This is known as dynamic pressure and is proportional to v^2. So as impact velocity goes up the target (gel/flesh) gets exponentially “harder” as can’t get out of way of bullet fast enough. A bullet manufacturer lists where their bullet will have enough pressure to deform given the expected application. For ex, it may take 2000 fps for a bullet to even start to deform on a gel block but the bullet may shatter if hitting a steel plate or heavy bone at similar velocity. Otherwise there is more than enough energy to deform a bullet/do damage but impact velocity, bullet construction, and target density enable it.

Lou

 

[Lou270]

What does a rock have to due with tissue.

If you understood terminal ballistics you would understand the point

Lou

 

[bmart2622]

^^^^Ohhhh the irony of this comment!!

 

[Koda_]

Think about it this way. It only takes a couple hundred ft-lbs for a bullet to deform (depends on a bunch of stuff). However a bullet is much more dense than flesh. A bullet needs to hit at a certain speed to make the target harder than the bullet so it will deform. This is known as dynamic pressure and is proportional to v^2. So as impact velocity goes up the target (gel/flesh) gets exponentially “harder” as can’t get out of way of bullet fast enough. A bullet manufacturer lists where their bullet will have enough pressure to deform given the expected application. For ex, it may take 2000 fps for a bullet to even start to deform on a gel block but the bullet may shatter if hitting a steel plate or heavy bone at similar velocity. Otherwise there is more than enough energy to deform a bullet/do damage but impact velocity, bullet construction, and target density enable it.

Lou

When I read that it seems like your admitting velocity expands the bullet. If it only takes a couple hundred ft-lbs to expand a bullet then why do they fail to expand at low velocity?

 

[9.1]

How long is a 270 win cartridge with the 155gn LRX seated to an appropriate depth? Will it fit in your magazine? Will you be able to send a dummy round to the person chambering your new barrel?

 

[Reburn]

man this thread has been a pretty painful read all in all.

 

[Lou270]

So how much ft-lbs of energy does it take to upset a Barnes bullet?

What does a rock have to due with tissue.

When I read that it seems like your admitting velocity expands the bullet. If it only takes a couple hundred ft-lbs to expand a bullet then why do they fail to expand at low velocity?

Reread my post on dynamic pressure if didnt get why something may not expand at low velocity. Velocity is a vector. It is a rate of change in a direction. It cannot “expand anything”. Energy is the potential to do work ie the capacity to exert force or cause change in a system. The transfer of energy is what does the wounding whether bullet expands or not. For ex, tumbling works just fine just not predictable

I am not trying to get in a philosophical discussion on how much energy is needed for whatever just stating how it works

Lou

 

[Lou270]

Barnes lists load data for 270 win with 155 lrx loaded to 3.34 on their website so should work in 270 Win saami chamber. Probably means they could have made a bit more aerodynamic but good news for those thinking on rebarreling a 270

As for 6.8W it is great cartridge. I have 2 and that is way I would go though I am a 270 Win fan so can understand why would want to stick with the old girl. The 6.8W is a Sweetheart to load for. Very accurate and no issues hitting advertised velocities with handloads or factory loads. Recoil is little more than 270 but mild with brake or can. Only down side had been brass in the past but Winchester has been doing more regular drops and ADG is making it. Win/Browning have a bunch of factory loads and have had no problems finding factory ammo. Barnes seems to be about to introduce a 6.8W factory load as well, at least they had a recent FB post inferring it.

Lou

 

[Formidilosus]

Reread my post on dynamic pressure if didnt get why something may not expand at low velocity. Velocity is a vector. It is a rate of change in a direction. It cannot “expand anything”. Energy is the potential to do work ie the capacity to exert force or cause change in a system. The transfer of energy is what does the wounding whether bullet expands or not. For ex, tumbling works just fine just not predictable

I am not trying to get in a philosophical discussion on how much energy is needed for whatever.

Lou

No, you’re telling us what the price of tea in china is

Ft-lbs of energy at impact gives zero (0) usable information about what depth, width, and shape a wound from a specific bullet will be- it is functionally useless. Too se that as any form of differentiator between bullets or as a marker for killing ability has no function.




To all, and the OP @alpinewanderer:

Ballistics kill by destroying tissue, and/or impairing vital organ function- ft-lbs of energy is a functionally useless metric and does not tell you anything about the depth of penetration, width of the permanent and temporary cavity, neck length, or the overall shape.

The gold standard for terminal ballistics testing (and used by nearly 100% of legitimate bullet manufacturers), and the only medically validated in tissue method is using calibrated 10% organic gel and various barriers; backed up with live tissue validation/checks.



1). Pick a specific bullet.

2). Shoot it into calibrated bare gel and with barriers at different impact velocities- measure the wounds correctly.

3). Book end validate those findings in animals.

At no point is ft-lbs of energy even spoken about, let alone used.

 

[Lou270]

No, you’re telling us what the price of tea in china is

Ft-lbs of energy at impact gives zero (0) usable information about what depth, width, and shape a wound from a specific bullet will be- it is functionally useless. Too se that as any form of differentiator between bullets or as a marker for killing ability has no function.




To all, and the OP @alpinewanderer:

Ballistics kill by destroying tissue, and/or impairing vital organ function- ft-lbs of energy is a functionally useless metric and does not tell you anything about the depth of penetration, width of the permanent and temporary cavity, neck length, or the overall shape.

The gold standard for terminal ballistics testing (and used by nearly 100% of legitimate bullet manufacturers), and the only medically validated in tissue method is using calibrated 10% organic gel and various barriers; backed up with live tissue validation/checks.



1). Pick a specific bullet.

2). Shoot it into calibrated bare gel and with barriers at different impact velocities- measure the wounds correctly.

3). Book end validate those findings in animals.

At no point is ft-lbs of energy even spoken about, let alone used.

Never said energy did any of those things. I was just explaining velocity does not expand bullets and how it really works. Velocity alone tells you nothing about the things you listed either including killing ability

Lou

 

[Koda_]

I was just explaining velocity does not expand bullets and how it really works. Velocity alone tells you nothing about the things you listed either including killing ability

Im going to bold highlight the places your saying velocity expands the bullet.

Think about it this way. It only takes a couple hundred ft-lbs for a bullet to deform (depends on a bunch of stuff). However a bullet is much more dense than flesh. A bullet needs to hit at a certain speed to make the target harder than the bullet so it will deform. This is known as dynamic pressure and is proportional to v^2. So as impact velocity goes up the target (gel/flesh) gets exponentially “harder” as can’t get out of way of bullet fast enough. A bullet manufacturer lists where their bullet will have enough pressure to deform given the expected application. For ex, it may take 2000 fps for a bullet to even start to deform on a gel block but the bullet may shatter if hitting a steel plate or heavy bone at similar velocity. Otherwise there is more than enough energy to deform a bullet/do damage but impact velocity, bullet construction, and target density enable it.

Lou

 

[Macintosh]

As for bullet expansion, velocity does not expand bullets. Impact velocity makes a soft/liquid target “harder” than the bullet (dynamic pressure) such that the bullet deforms until slows down enough during penetration that the bullet is again “harder” than the target and stops deforming. This happens very early during penetration as the bullet slows down quickly once deforms. Energy is what deforms the bullet.

Lou

Help me out here. We have a standard tissue analogue (gel) so we can estimate that hitting an animal is a constant medium. So we can say at x velocity our medium “hardens” enough to upset this bullet, and below Y velocity it doesnt “harden” enough to upset. I think (??) we all know that the velocity by itself isnt doing the work, but rather that the velocity is PREDICTIVE of upset in the only medium we’re talking about. We know ft lb of energy as in velocity x bullet mass is useless, or else fmj bullets would kill critters the same as an expanding hunting bullet, and they dont. So how does using velocity as the predictor of upset on flesh and bone contradict what you are saying about what actually does the work of upsetting the bullet?

No one is saying “2000fps does the work of expanding a ttsx bullet”, they are saying “2000fps is a recommended minimum velocity to achieve consistent expansion on game”. Which accounts for the physics of that interaction, with the velocity being the one significant variable that is most predictive. If not this way, How would YOU say this?