None... it is the same sized bullet (.308 diameter). You have to choose the selection of bullet when reloading 30-30 ammo for the type of bullet. A pointed bullet in a tubular magazine can present a problem when the rifle recoils. The ammo is not interchangable, you must shoot the ammo that the rifle was chambered for.
The .308 has a shorter cartridge case, and a fatter bullet. The .270 is based on the 30-06 case, about a quarter inch longer than the .308 case.
The 30-30 is a rimmed cartridge, versus the .308, which has a rimless cartridge. The 30-30 has much lower energy than the .308, and is typically loaded with a flat tipped bullet, due to the number of lever action 30-30s that had a tubular magazine. The .308 typically has a spitzer (pointed) bullet.
GTFO
The .308 Winchester bullet is typically larger in diameter than the .270 Winchester bullet. The .308 has a bullet diameter of .308 inches, while the .270 has a diameter of .277 inches. However, the .308 bullet generally has a heavier weight and greater case capacity, which can affect overall performance and use. Both cartridges are popular for different types of hunting and shooting applications.
308...A 7.62mm = .300
First, there are BULLETS and there are CARTRIDGES- then there is US and then there is Europe. In the US, a .308 bullet IS a 7.62 mm bullet. The .308 Winchester CARTRIDGE is similar to, but slightly different from the 7.62 NATO cartridge. The .308 has minor differences in the case measurements, has slightly less internal volume (due to thicker military brass) and is loaded to higher pressures that the military 7.62 NATO. The NATO round can be safely fired from a .308 Winchester rifle, but the reverse is not true. In Europe, they measure bore diameter differently than the US does. Due to the different measuring technique, what the Europeans CALL a 7.62 mm (like the 7.62x39 cartridge for the SKS) is really closer to .311 than .308.
Negative, 308 is a 30 caliber bullet and 30 doesn't fit into 25.
Given the limited information in your question I can only give a general reply. The caliber is the diameter of the rifle groove to groove in thousands of inches. So the difference would be .450" - .308" which equals .142". There are a lot of specified rounds of ammunition that use .308 and .450 bullets. In general the larger caliber bullet would also be more powerful.
2m
Typically between 2600 and 2800 feet per second. Exact speed depends on WHICH bullet, the powder charge, and the length of barrel it is fired from.
The Savage .308 rifle can typically accommodate a range of bullet grains. It is important to check the specific firearm's manual or consult with a knowledgeable gunsmith to determine the optimal bullet weight for your rifle based on factors such as barrel twist rate and intended use. Generally, bullet weights between 150 and 180 grains are commonly used in a .308 rifle.
Sorry, you need to specify WHICH .308 bullet and at what distance. As distance increases, the RATE of drop also increases.