Most early firearms were muzzle-loading. This form of loading has several disadvantages, such as a slow rate of fire and having to expose oneself to enemy fire to reload as the weapon had to be pointed upright so the powder could be poured through the muzzle into the breech followed by the ramming the projectile into the breech. As effective methods of sealing the breech were developed through the development of sturdy, weatherproof, self-contained metallic cartridges, muzzle-loaders were replaced by single-shot breech loaders. Eventually single-shot weapons were replaced by the following repeater type weapons.