Yeah I typed in 75mm anti tank shell on google and that was what I found. I had no idea that you guys were working on such a weapon and I am massively impressed. Obviously this would be a difficult thing to do but would it somehow be possible for you to design this weapon so that it needs a small team to operate? You know, to load, fire, and move this cannon using a team would not only be realistic, but also interesting and immersive. It should not be too important to make this weapon fuction as realistic as possible and I know it would cause extra work but I do think that it would be utterly awesome if you manage to do this.
Good luck dudes, and what a good idea!