Under an Einstecklauf, one refers to a barrel that is inserted into the actual, usually permanently mounted barrel of a handgun. It is then locked in place via a mechanism so that it is firmly integrated into the weapon.
The purpose of such an Einstecklauf is to fire ammunition of smaller calibers from a barrel system originally designed for larger calibers. Einsteckläufe are used in both competitive shooting and hunting.
Of course, there must be a certain size or diameter difference between the actual, permanently mounted barrel and the Einstecklauf, so that the Einstecklauf can be inserted into the actual barrel of the weapon. Therefore, Einsteckläufe usually have small caliber.
Especially in the hunting sector, Einsteckläufe are used to fire shotgun rifle ammunition.