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 of an automatic injection device. The automatic injection device comprises a housing; a medicament chamber having a first compartment and a second compartment, the first compartment containing a first medicament portion and the second compartment containing a second medicament portion to be mixed with the first medicament portion; a seal structure between the first compartment and the second compartment, the seal structure initially in a sealing condition that maintains the first compartment separate from the second compartment; a needle assembly that dispenses the medicament charge from the medicament chamber, the needle assembly comprising a needle and a needle support, the needle support for mounting the needle to the medicament chamber, the needle support defining a needle assembly chamber having an inner surface that tapers radially inward as it extends axially forward toward a rearward end of the needle, the needle support forming a channel from the medicament chamber to the needle; and an activation assembly. 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 to be mixed, and (c) the mixed first and second medicament portions to be forced through the needle assembly.