Case Dimensions and Pressure ?'s

[Earnhardt]

OK, Big time newbie question here.

When changing case dimensions and neck angle of a cartidge how drastically does that effect chamber pressures and velocity?
When using the same exact weight bullet and powder how much more velocity and chamber pressure will a .300 WSSM have than a .300 Win Mag
Or, let's say you have a straight walled cartridge like a .458 Win Mag. If you took that same weight bullet and same weight/type powder and turned the cartridge into a wildcat cartridge how much would that effect pressure and velocity?
A 5% increase in pressure and velocity?

How about the opposite. Take a 6mm PPC cartridge and use the same weight bullet and same weight/type powder in a straight walled case.
How much would the decrease pressure and velocity?
5%?

Or doesn't it effect velocity and chamber pressure that much by changing the dimensions of the powder case while using the same weight bullet and powder?

Thank you for your time.

[Bart B]

Best place to find out is probably SAAMI's document below:

http://www.saami.org/specifications_...wnload/206.pdf

Check two cartridges with the same bore and with the same bullet weight for their pressure and velocity data to see how they compare.

Also, compare the two rounds' loading data on sites that list the charge weight and pressure; Hodgdon's is a good one.

[Earnhardt]

Thank you!