One aspect relates to an automatic injection device containing a pre-loaded charge of medicament for automatically administering the medicament upon actuation thereof. A further aspect relates to a method of providing a medicament containing chamber (350) of an automatic injection device. The automatic injection device comprises a housing (110)； a medicament chamber (350) having a first compartment and a second compartment, the first compartment containing a first medicament portion (151) and the second compartment containing a second medicament portion (152) to be mixed with the first medicament portion (151)； a seal structure (380) between the first compartment and the second compartment, the seal structure (380) initially in a sealing condition that maintains the first compartment separate from the second compartment； a needle assembly (340) that dispenses the medicament charge from the medicament chamber, the needle assembly (340) comprising a needle (141) and a needle support (343), the needle support (343) for mounting the needle (141) to the medicament chamber (350), the needle support (343) defining a needle assembly chamber (394) having an inner surface that tapers radially inward as it extends axially forward toward a rearward end of the needle, the needle support (343) forming a channel from the medicament chamber (350) to the needle； and an activation assembly (120). Activation of the activation assembly causes (a) the seal structure to be converted from the sealing condition to a mixing condition, (b) the first and second medicament portions (151,152) to be mixed, and (c) the mixed first and second medicament portions to be forced through the needle assembly (340).
