260Rem vs. 7mm-08: Need Help Undestanding

[Jakes10mm]

I need help understanding some rifle cartridge basics. I build a 260rem on a Savage action and have been looking through different load data. I happened to stumble on the fact that according to the reloading manuals, 7mm-08 can be loaded with bullets of equal weight to the 260rem, yet the 7mm-08 is significantly faster with less pressure. Is this a result of popularity of the 7mm-08 and better data development or something to do with the physics of the bore diameters of the two calibers? Just curious...thanks.

 

[bgjohn]

The bigger the hole, the lower the pressure. All else being equal.
JM

 

[Asa_Yam]

If

* force = pressure x area = mass x acceleration

and

* velocity = acceleration x time

Given equal mass and pressure, the bigger hole allows more force to be imparted on the base of the bullet. Over the same amount of time, the greater acceleration of the larger bullet = greater velocity.

 

[Jakes10mm]

Makes total sense, guess that explains why the powder loads are lighter on the 260 rem and velocity is down too.

 

[bgjohn]

If

* force = pressure x area = mass x acceleration

and

* velocity = acceleration x time

Given equal mass and pressure, the bigger hole allows more force to be imparted on the base of the bullet. Over the same amount of time, the greater acceleration of the larger bullet = greater velocity.

Yes, but it takes more powder to make equal pressure with the larger bore.

Another thing to remember is that the 6.5mm bullet has a better BC than the 7mm and therefore more V downrange. I'll admit I like the 260 better than the 7mm/08.
JM

 

[bgjohn]

If you can't decide, buy them BOTH!
JM

 

[crosshairs]

If you think the .260 has better BC than a 7mm you had better check that. Berger is making some seriously high BC 7mm bullets that I don't think even compare to the .260. Not trying to start an argument, just stating fact.

 

[memilanuk]

Maybe so... but then you get into the question of whether the 7mm-08 has enough boiler room to drive those big heavies to a useful velocity where they out perform the 6.5 140gr pills. Big bullets w/ big numbers are nice, but it usually takes a big case and lots of powder,and more recoil) to take advantage of them.