Does barrel length change magazine requirements?

How much does changing barrel length, but not caliber, affect the magazine?

Not very much; keeping the same caliber leaves the magazine requirements broadly similar.

Barrel length alone has little effect on the magazine when calibre remains unchanged. A longer or shorter barrel alters the gun installation without automatically changing the diameter of the ammunition it consumes. Magazine consequences become more important when a navy introduces different shells or propellant arrangements. The answer separates the dimensions of the weapon from the ammunition-handling spaces below deck.