The cartridge is sometimes called the .303 Enfield or .303 British (or even 7.7×56mmR). Do not attempt to use other ammunition.
The .303 British and .303 Savage are not the same. Only purchase the caliber that is printed on the barrel.
Assuming you mean a rifle such as the SMLE, the cartridge used in the .303 Enfield, also called .303 British. See the link below for information on this ammo. However, if you are not certain (some military surplus rifles were rebarreled into other calibers) have a gunsmith take a look at it.
The ,303 Enfield British rifle cartridge is fairly popular, Most well supplied gun shops will carry this ammo, and with adequate proof of age, can be purchased from on-line suppliers.
Yes, you can shoot .38 ammo in a .357 firearm. The .357 firearm is designed to also shoot .38 caliber ammunition.
If you mean CARTRIDGES for a .303 Enfield rifle, also known as .303 British, depends on which cartridge, and where you are. In Virginia in the US, civilian hunting ammo may retail for $35/ 20 rounds. Careful shopping for surplus ammo may be less.
No.
It shoots better with the ammo box
Yes
No.
Catalogs, gun shops, sporting goods stores, etc..
No. Only shoot the caliber printed on the barrel.
Yes.