A number of designs were produced during WW1 for large or medium artillery based on the Davis recoiless principle whereby a counterweight was fired rearwards out of a second barrel by the same charge that fired the shell out of the main barrel. These were much larger than the various Davis weapons that were intended for aircraft. Typically they were to be mounted on tall gantries, this allowed the gun to be elevated as there had to be clearance to allow the rearward facing second barrel to swing downwards. This would have ]made loading awkward. A Mr Davison came up with a design to be truck mounted. The truck engine drove Archemedes screws that raised and lowered the gun which was mounted on a steel column. This allowed the gun to be loaded under cover and then raised for firing (much like a disapearing mount). Had such a gun been built it would have had some problems including the effects of the rearward fired counterweight on its own side. If the gun was elevated this charge would blast into the ground fairly close to the gun itself, especially if it were firing from a dug in emplacement. An additional problem would have been the flach from the breech in the middle of the gun. Davis never succeeded in producing a consistently gas tight breech (and missing eyebrows and scorch marks became a trade mark of those developing this weapon). It is unlikely that a larger gun would have been any better. Firing such a weapon could have been terminally uncomfortable.
The method of raising the carraige does seem designed to partially mitigate the Davis' Gun's 'bad habits', but yes, it probably wouldn't have worked terribly well. Was a size listed for this piece? It looks to be in the 12-15cm range...and one other question, did Davis guns use a conventional cartridge, or was the propellant charge increased relative to the shell, as in later Recoilless guns?
Can't answer much of this without further digging but I don't think that the propellant was increased. The later WW2 recoiless such as the Burney and the post WW2 BAT WOMBAT, MOBAT etc all used high velocity gas as the counter weight and they needed extra propellant to generate this. The original Davis design actually fired the breech as the counter weight making it a one shot weapon but later models used a charge of lead shot encased in beeswax as the counterweight. This should not have required extra propellant.
