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Yep. It depends on the cartridge, but in general improved cases tend to extend barrel life, because the sharper shoulder angles more of the powder gas to hit the inside of the case neck, rather than the bore in front of the neck. The little bit of extra powder used in improved cases also isn't enough to make any difference in barrel heat, which is the major factor in bore life.
On the other hand, improved cartridges don't gain very much velocity over their parent cases WHEN LOADED TO THE SAME PRESSURE. The reports of improved cases gaining 200+ fps are due to comparing the velocities of worked-up handloads (usually without any pressure testing) to factory ammo or pressure-tested handloads for the parent case. In reality very few improved rounds will gain as much as 100 fps WHEN LOADED TO THE SAME PRESSURE. Those tend to be older rounds with tapered bodies, such as the .250 Savage and .300 H&H. In a round with relatively little taper, such as the 6.5x55, the same-pressure gain is less than 100 fps, often considerably less. Not sure if I'm mis-interpreting your comments MD, but the 6.5x55 ( with .480" base - 436 " shoulder ) has as much or more taper ; as a .270Win or .30'06 ( with their .470" base - .441" shoulder diameter) The modern 6.5 CM has very little taper with .470" base, and .462" shoulder diameter The .250 Savage, and .300 H&H do have a bunch of taper. 7x64 is another that comes to mind, and is often compared to the .280, but it is loaded to higher pressure levels
History May Not Repeat, But it Rhymes.
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[quote=Mule Deer]
Not sure if I'm mis-interpreting your comments MD, but the 6.5x55 ( with .480" base - 436 " shoulder ) has as much or more taper ;
as a .270Win or .30'06 ( with their .470" base - .441" shoulder diameter)
I took this as being relative to rounds like the 300 H&H and 30-30 compared to relatively modern ones like the 1897 Swede.
"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli
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Joined: Oct 2010
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[quote=Mule Deer]
Not sure if I'm mis-interpreting your comments MD, but the 6.5x55 ( with .480" base - 436 " shoulder ) has as much or more taper ;
as a .270Win or .30'06 ( with their .470" base - .441" shoulder diameter)
I took this as being relative to rounds like the 300 H&H and 30-30 compared to relatively modern ones like the 1897 Swede. Yup, that's modern for some curmudgeons  .308 family have .470" base, and .454" shoulder . The CM has the least I'm aware of at .462" shoulder Good luck with your Forbes !
History May Not Repeat, But it Rhymes.
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Campfire Tracker
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Yep. It depends on the cartridge, but in general improved cases tend to extend barrel life, because the sharper shoulder angles more of the powder gas to hit the inside of the case neck, rather than the bore in front of the neck. The little bit of extra powder used in improved cases also isn't enough to make any difference in barrel heat, which is the major factor in bore life.
On the other hand, improved cartridges don't gain very much velocity over their parent cases WHEN LOADED TO THE SAME PRESSURE. The reports of improved cases gaining 200+ fps are due to comparing the velocities of worked-up handloads (usually without any pressure testing) to factory ammo or pressure-tested handloads for the parent case. In reality very few improved rounds will gain as much as 100 fps WHEN LOADED TO THE SAME PRESSURE. Those tend to be older rounds with tapered bodies, such as the .250 Savage and .300 H&H. In a round with relatively little taper, such as the 6.5x55, the same-pressure gain is less than 100 fps, often considerably less. Not sure if I'm mis-interpreting your comments MD, but the 6.5x55 ( with .480" base - 436 " shoulder ) has as much or more taper ; as a .270Win or .30'06 ( with their .470" base - .441" shoulder diameter) The modern 6.5 CM has very little taper with .470" base, and .462" shoulder diameter The .250 Savage, and .300 H&H do have a bunch of taper. 7x64 is another that comes to mind, and is often compared to the .280, but it is loaded to higher pressure levels And AI cartridges based on the /06 family are among those which don't gain much velocity over the parent case. This is because the case capacity is not increased all that much. Even where case capacity is increased substantially, velocity gains are not always as great as supposed. where gains are significant, it usually occurs in cases where the parent case just would not hold enough of a given powder to build sufficient pressure. I have always believed the theory regarding extended throat life but am aware of no real testing. An early mentor told me, if a line drawn along the shoulder impinged on the neck rather than in the throat, barrel life would be enhanced and I had no reason to doubt this. The 6.5x55 shoulder is sharp enough to accomplish this and barrel life seems to be fairly good. GD
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