This penetration/velocity/expansion thing is kinda hard to pin down sometimes
I think what JB says is correct in general.But i thnk it is hard to generalize about bonded bullet performance today because they come in such a wide variety of construction types,materials(pure copper vs guilding metal jackets;pure lead cores vs antimony),different bonding techniques,the absence or presence of mechanical devises to limit expansion (partitions like the Aframe, or solid rear sections like the TTBC or Northfork),and jacket thickness.
All these factors can add up in any one design to affect expansion at different velocities,and penetration.Add the variables like impact velocities,and the medium contacted(ribs/lungs vs shoulders, etc.)and you wind up with so many variables it becomes pretty hard to draw concrete conslusions about any one design until you see them work over a wide range of animals and conditions.
I am a fan of bonded bullets but a lot of my experiences are limited to the old original,the Bitterroot,which I have used a pretty fair amount since the 80's,and in a few different cartridges.Prior to that time, I read of their use by guys like John Wooters and Bob Hagel,and some others,who created a stir and led to many designs we have today.For example, it was Jack Carter's inability to get Bill Steigers to mass manufacture the Bitterroot, that led to Carter's development of the original TBBC. I know this because years back I would speak with Steigers on the phone 2-4 times a week, for years.Also,floating around somewhere,there is an article by the designer of the Northfork,indicating that he was trying to emulate the Bitterroot performance with the NF;same/same with Lee Reid and the Swift Aframe.These bullets behave much the same way with a few minor differences.
I have freinds who have used the bullet as well,so some of this is anectdotal.
The BBC was made of very heavy pure cooper jackets, as much as .060 jacket thickness;and pure lead cores,bonded by a technique that was then proprietary.They were essentially a cup/core design,with no mechanical devise to stop expansion other than the thick heavy jackets and the bonding..
They were very "tough",and Steigers recommended not only minimum velocities for thier use, but minimum twist rates as well.His expansion tests indicated that a faster twist,coupled with higher impact velocties, resulted in more dramatic expansion,especially at distance.
They have always been dramatic killers due to early and wide expansion.They will never fragment,and the expamded wings will not shear even under extreme stress ( have seen one wing come off but the bullet tumbled,having defleced on a branch before impact).Generally penetrate as far as needed,frequently farther,and at close range,will almost always be stopped against hide on the far side, but will reliably smash both shoulders on about anything.
Thi wide,rapid expansion has given me a lot of DRT's even with pure lung hits. I recall one black bear of about 300 pounds that I killed with the 280 and 140 BBC,where I hit nothing but ribs and lungs at about 90 yards. It collapsed immediately and never got to its feet....this is not easy to do with a bear. I have seen them hit likewise with other bullets and run like a scalded cat.Expansion was about 60 caliber, and retained weight about 138 gr.
One large mule deer was hit quartering on at the point of the shoulder,distance about 70 yards to a 140 gr driven over 3250 from a 7RM;he collapsed to the shot....the bullet was recovered clear back in the opposite ham,again expanded to about 60 caliber,and retaining about 95% weight.
Velocity makes a difference; I have noticed that the 130 gr from a 270 Win at 3100,will exit lung hits or shoulder hits on large deer out around the 300 yard mark,due to reduced expnasion and lower velocity....yet a 140 7mm at the same distances,and MV @ 3250-3300 will still be recovered against that rubbery off side hide.The extra velocity causingwider expansion, even at distance.
It is apparent that destruction is just greater at the higher velocities...have had the 165 30 cal driven 3250 from a 300 Win Mag turn the chest cavity of a bull elk to soup and break the offside shoulder,then exit at about 225 yards.
These and other observations are why I gently argue sometimes with folks who advocate very thin jacketed bullets as being the more rapid killers of deer sized game.This has not been my exoerience, entirely...I know that theory "works", but also know that the very rapid exansion of a quality bonded bullet,and high velocity will also destroy a lot of internal tissue,and still have enough mustard to handle bone the other side of the wound channel....what happens after that really doesn't matter.
If I had to count on a bullet to "dump" a big mule deer or whitetail(or elk),on his nose at tough angles from 350-400 yards or so, on in,I would rather run a Bitterroot or Swift Aframe at magnum velocities than a more fragile bullet,or anything else for that matter.
Just my cents on the matter....this bonded bullet stuffcould take up a book!
