syringes using pre - loaded cartridges for injecting fluid medications can be made safer for users and patients , more compliant with modern infection - control precautions , and easier to operate by supplying thumb - ring activated , breech - loading syrettes with screw - on plungers for aspirating into and emptying transparent cartridges with permanently attached needles . the cartridges can be made with trailing terminal circular flanges with gaps for stabilizing the cartridge in the syrette breech chambers closed by hinging breech blocks ; permanently attached leading needles whose exposed tips are kept sterile before use by thin disposable elastomeric scabbards ; and whose trailing ends optimize visualization of flashback . such &# 34 ; shot - guns &# 34 ; consisting of reusable breech - loading syrettes and disposable pre - loaded transparent cartridges with attached needles can be supplied with two part puncture resistant plastic scabbard systems and trailing caps which integrate to keep the cartridges and needles sterile before use ; which can be used as a convenient sterile holders for loaded or partially unloaded cartridges inside the syrettes , and which implement safe ejection of empty disposable cartridges with permanently attached needles from the breech chambers of the syrettes into sharps containers , thereby minimizing opportunities for hazardous needle - stick injuries .