Case capacity/bullet intrusion question

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Was thinking about this on my morning drive and couldn't work it out so I thought I'd ask folks here who have a lot more experience with firearms and reloading than I have.

I understand the premise of the 6.5 CM and the PRC's (basically all the latest modern cartridges) that are designed to allow you to seat the high BC long bullets further out to engage the lands without protruding deep into the case. Makes sense.

But here's what I can't quite figure out. Let's take the .260 Rem and the 6.5 CM for example. The same 143 ELD-X will protrude quite a ways into the .260 case and not nearly as far into the CM case. BUT, the 260 case is larger to begin with so at the end of the day don't they basically both have the same amount of powder space?

So is the point of the newer cartridge designs (aside from the obvious benefits of a steeper shoulder extending case life and reducing trimming frequency) a more efficient powder "chamber"?

Same could be said for the 7RM and the 7PRC I guess, and others.

Someone with more knowledge and experience in cartridges please 'splain.

Thanks!
 

XLR

WKR
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What they are doing with all of the new cartridge designs is optimizing them for the new higher BC bullets. To optimize them they are not only changing the case design but also changing the free bore and lead angles. For example the 260 Remington has a Sammi free bore of .119" and a 3 degree lead angle. The 6.5 Creedmoor has a .200" free bore and a 1.5 degree lead angle. For the free bore specifically this allows factory ammo to be loaded with bullets seated out further than what's offered in the 260. The lead angle is just going to change how the bullet approaches the lands which is a whole different topic.

Custom chambers and hand loading allows shooters to easily bring older cartridges up to speed! For example the 260 Remington reamer print I attached is from panhandle precision. He kept the same case design but pushed the free bore to .250" with the 1.5 degree lead. So this rifle now has similar characteristics to the 6.5 creed BUT no factory ammo is going to allow him to optimize the chamber so he will need to reload.

The other part that comes into effect is the twist rates that rifles are built with. Hornady could manufacture some 243 ammo and jam a 108 ELDM in but that would require at least a 1:8 twist barrel. 90% of people do not even know what the twist of their rifle is let alone what the best twist for bullet size would be. So then they would run into the issue of shooters running that ammo in a 1:10 twist rifle and it would not shoot great leaving a bad reputation for Hornady. By creating a 6mm creedmoor Hornady can simply load the ammo and know that 90% of the rifles produced are using a 1:8 twist barrel. This is why you will not see too many skus of 6mm Creedmoor ammo outside of the 90-110 grain range and you will also not see any 243 skus above the 90 grain.

So overall I think that the new calibers don't really bring anything new to the market chamber wise, but it does allow ammo manufacturers to maximize a cartridges performance for the newer higher BC bullets and make sure their customer service team is not swamped with complaints from shooters who are not educating themselves. I kind of veered off topic for a little but hopefully this sheds some light.
 
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Newtosavage
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What they are doing with all of the new cartridge designs is optimizing them for the new higher BC bullets. To optimize them they are not only changing the case design but also changing the free bore and lead angles. For example the 260 Remington has a Sammi free bore of .119" and a 3 degree lead angle. The 6.5 Creedmoor has a .200" free bore and a 1.5 degree lead angle. For the free bore specifically this allows factory ammo to be loaded with bullets seated out further than what's offered in the 260. The lead angle is just going to change how the bullet approaches the lands which is a whole different topic.

Custom chambers and hand loading allows shooters to easily bring older cartridges up to speed! For example the 260 Remington reamer print I attached is from panhandle precision. He kept the same case design but pushed the free bore to .250" with the 1.5 degree lead. So this rifle now has similar characteristics to the 6.5 creed BUT no factory ammo is going to allow him to optimize the chamber so he will need to reload.

The other part that comes into effect is the twist rates that rifles are built with. Hornady could manufacture some 243 ammo and jam a 108 ELDM in but that would require at least a 1:8 twist barrel. 90% of people do not even know what the twist of their rifle is let alone what the best twist for bullet size would be. So then they would run into the issue of shooters running that ammo in a 1:10 twist rifle and it would not shoot great leaving a bad reputation for Hornady. By creating a 6mm creedmoor Hornady can simply load the ammo and know that 90% of the rifles produced are using a 1:8 twist barrel. This is why you will not see too many skus of 6mm Creedmoor ammo outside of the 90-110 grain range and you will also not see any 243 skus above the 90 grain.

So overall I think that the new calibers don't really bring anything new to the market chamber wise, but it does allow ammo manufacturers to maximize a cartridges performance for the newer higher BC bullets and make sure their customer service team is not swamped with complaints from shooters who are not educating themselves. I kind of veered off topic for a little but hopefully this sheds some light.
That might be the best explanation I've heard yet and I really appreciate you taking the time to explain it.
 
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XLR

WKR
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That might be the best explanation I've heard yet and I really appreciate you taking the time to explain it.
Of course! I feel like sometimes as shooters we like to think it is a marketing fad for the new calibers but I think Hornady is actually hitting the nail on the head with a lot of these new calibers!
 
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