abutment to provide a seating for the primer cap in the first second and third embodiments the missile 10 is disposed in the second portion of the chamber 23 the diameter of the second portion is slightly less than the maximum diameter of the missile before the latter is inserted into the casing 12 thus even if the skirt 16 is not trapped between the insert and the internal shoulder the missile will be held by friction in this second portion the first three embodiments are assembled by inserting the missile 10 through the base opening 24 and first portion 27 into the second portion 28 of the chamber 23 prior to the insert 13 and the primer cap 11 being inserted into the casing 12 so as not to damage or distort the missile skirt 16 the third embodiment may be sold ready assembled as a disposable round of ammunition the fourth embodiment shown diagrammatically in fig7 is similar to the first embodiment except in that the insert 13 is of composite form to define a mouth 38 in which the missile 10 is accommodated the insert comprises an outer tubular member 40 and an inner tubular member 41 which defines the passage 30 and is slidably accommodated in the member 40 so as to abut a second internal shoulder 42 the mouth 38 extends from said shoulder 42 within the end 37 of the insert in the fourth embodiment the cap 11 is a push fit in the member 40 and the inner member 41 serves as an abutment to provide a seating for the cap 11 in the fourth embodiment the missile can be inserted nose first into the outer member.