|Regenerative Liquid Propellant Guns have apparently been studied for some time. Other than being mechanically complex - as either a mono or binary propellant must be pumped into the chamber at each firing - with admittedly minimal research I've not found why no such gun has been fielded. Their would seem to be many advantages: easy adjustment of amount of propellant to adjust range, less fouling of barrel (?), more compact storage. Safer storage when using binary systems etc. Charts I looked at even indicated better performance and perhaps pressures beyond those attainable by solids. Though studied mainly for cannon, I would think you could almost scale these things to personal weapons. So why no RLP Gun yet?