25-06 270 30-06

[scope eye]

Why is it that the same basic cartridge has such a big spread in powder amount?
25-06 120gr bullet 41gr varget max load
270 120gr bullet 47gr varget max load
30-06 120gr bullet 57gr varget max load
per hogdon websight
This may or mat not be the best example but it is pretty much the same down the line.

[stimpylu32]

While they may be about the size , they do have different case capisities .

25/06 = 4.15cc
270 w = 4.24cc
30/06 = 4.38cc

Also the amount of bearing surface in all 3 of the bullets is also different , and once you add in the fact that all 3 cartridges run at different pressure levels , that can explain some of the range in powder charges .

stimpy

[scope eye]

That's 33% less powder and the smaller bullet has the least bearing surface, and as far as psi they are basically the same case. I know there a lot of factors involved but it just seems like a wide separation between the three.
thanks Dean

[thirty06]

With all the bullet weights being the same, 120gr.
The smaller caliber, 25 will have more bearing surface.
Your pushing a longer bullet through a smaller hole, thus more pressure.

[stimpylu32]

well , lets look at a couple other things .

25/06 - 120g @ max = 2755 FPS at 45,100 CUP - Swift SP ( not sure )

270W - 120g @ max = 3010 FPS at 46,300 CUP - Barnes XFB ( Copper solid )

30/06 - 125g @ max = 3207 FPS at 49,500 CUP - Sierra SP ( Cup & Core )

While the 120g is at the top level of bullet weight for the 25/06 , yet the 125g is almost at the bottom of weight for the 30/06 , so while the bullets may be close to the same weight , the speed at which they leave the barrel is quite different , over 450 fps .

stimpy

[stimpylu32]

With all the bullet weights being the same, 120gr.
The smaller caliber, 25 will have more bearing surface.
Your pushing a longer bullet through a smaller hole, thus more pressure.


Now the bullet being longer is true , the numbers show that the 25/06 runs at a slightly lower pressure than the 30/06 ( 4,400 cup ) , I think part of this is due to the amount of surface area that is being pushed against on the base of the bullet .

stimpy

[Captain Finlander]

All true but terminal performance favors the longer bullet. The 120 grainer in the 25-06 will greatly out perform the 125 grainer from the 30-06 despite the 450 fps disadvantage. It comes down to sectional density and bullets with lower sectional densities do not hold together limiting penetration. Higher velocities also leads to greater expansion so the 125 grainer from the 06 will likely disintegrate before reaching any vitals while the 25 caliber 120 would not.

[kslefty]

My sierra manual lists the accuracy load for each of your scenarios, RL22 is listed for the 25-06 and varget for the 30-06. They are drastically different in burn rates but each uses 53gr of powder + or - .5 grains for their accuracy load. The speeds are within 100 fps so it is simply finding the correct match of bullet weight for caliber and burn rate.

[tammons]

Overbore and less case capacity as you go smaller, bore efficiency as you go larger.

The 30-06 will be more efficient pushing the same weight bullet down the barrel, IE the piston effect.

[scope eye]

I couldn't help noticing that the piston effect does not apply to weatherby caliber's, no where near as much spread I wonder why?

[tammons]

Not really sure, but they are improved magnum calibers, different shoulder etc.
Still even a bit more of an overbore since the case is fatter.

[Blue Avenger]

Dia of the powder burn jet coming down the barrel. Takes more powder to fill the larger barrel and hold the same pressure while pushing less % weight in relation to the dia of the barrel.

[BrentWin]

Dia of the powder burn jet coming down the barrel. Takes more powder to fill the larger barrel and hold the same pressure while pushing less % weight in relation to the dia of the barrel.


+1

As the bullet travels down the barrel, the volume of the barrel is added to the volume of the case. Thus .257 dia barrel will have less total volume and will require less powder to maintain the same pressure