An injection device comprising: a barrel extending axially between a distal end and a proximal end, the barrel configured to contain a medicinal fluid, the barrel comprising a first retaining ring proximate to the proximal end; a plunger rod having a distal end and a proximal end, the distal end of the plunger rod disposed in the barrel; and a stopper assembly disposed in the barrel, the stopper assembly comprising: a stopper having a laterally outermost surface configured to be directly engaged with an inner surface of the barrel; and a sealing element coupled to and axially distal relative to the stopper in the barrel, the sealing element having a laterally outermost surface configured to be directly engaged with the inner surface of the barrel and to sealingly isolate the stopper from the medicinal fluid in the barrel the injection device characterized in that: the barrel comprises a second retaining ring located proximate to the proximal end of the barrel, the first retaining ring axially spaced apart from and located proximal relative to the second retaining ring, the first and second retaining rings (203, 205) defining a minimum lateral dimension (D 203, D 205) of the inner surface of the barrel; and wherein each of the sealing element, the stopper, and a flange of the plunger rod is located between the first and second retaining rings (203, 205) in the storage position such that the stopper is axially compressed between the sealing element and the flange of the plunger. a barrel extending axially between a distal end and a proximal end, the barrel configured to contain a medicinal fluid, the barrel comprising a first retaining ring proximate to the proximal end; a plunger rod having a distal end and a proximal end, the distal end of the plunger rod disposed in the barrel; and a stopper assembly disposed in the barrel, the stopper assembly comprising: a stopper having a laterally outermost surface configured to be directly engaged with an inner surface of the barrel; and a sealing element coupled to and axially distal relative to the stopper in the barrel, the sealing element having a laterally outermost surface configured to be directly engaged with the inner surface of the barrel and to sealingly isolate the stopper from the medicinal fluid in the barrel the injection device characterized in that: the barrel comprises a second retaining ring located proximate to the proximal end of the barrel, the first retaining ring axially spaced apart from and located proximal relative to the second retaining ring, the first and second retaining rings (203, 205) defining a minimum lateral dimension (D 203, D 205) of the inner surface of the barrel; and wherein each of the sealing element, the stopper, and a flange of the plunger rod is located between the first and second retaining rings (203, 205) in the storage position such that the stopper is axially compressed between the sealing element and the flange of the plunger. a stopper having a laterally outermost surface configured to be directly engaged with an inner surface of the barrel; and a sealing element coupled to and axially distal relative to the stopper in the barrel, the sealing element having a laterally outermost surface configured to be directly engaged with the inner surface of the barrel and to sealingly isolate the stopper from the medicinal fluid in the barrel the injection device characterized in that: the barrel comprises a second retaining ring located proximate to the proximal end of the barrel, the first retaining ring axially spaced apart from and located proximal relative to the second retaining ring, the first and second retaining rings (203, 205) defining a minimum lateral dimension (D 203, D 205) of the inner surface of the barrel; and wherein each of the sealing element, the stopper, and a flange of the plunger rod is located between the first and second retaining rings (203, 205) in the storage position such that the stopper is axially compressed between the sealing element and the flange of the plunger. the barrel comprises a second retaining ring located proximate to the proximal end of the barrel, the first retaining ring axially spaced apart from and located proximal relative to the second retaining ring, the first and second retaining rings (203, 205) defining a minimum lateral dimension (D 203, D 205) of the inner surface of the barrel; and wherein each of the sealing element, the stopper, and a flange of the plunger rod is located between the first and second retaining rings (203, 205) in the storage position such that the stopper is axially compressed between the sealing element and the flange of the plunger.