In Australian trials with the Sheridan they were rather alarmed to see the Sheridan's not only lift but the entire vehicle move backwards a metre, with brakes hard on, when firing forwards. They refused to fire it athwartships, fearing the entire vehicle would flip. The Sheridan was seriously over gunned. When the gun fired conventional ammunition it used to shake the missile optics out of alignment as well, in the early days, which meant the missile system couldn't be re-used.
On top of that, because the conventional rounds used a fully combustible cartridge case, made of cardboard, there were problems in the early days of the cases swelling from moisture, which meant they couldn't be loaded. They were also prone to splitting and spilling powder inside the vehicle. This was partly fixed by issuing the rounds in a large plastic sleeve, which the crews used to nickname "Elephant Condoms", which they had to strip just before loading. There were also problems with the cartridge cases not being properly and completely consumed during firing, leaving essentially still burning fragments in the chamber and barrel, leading to the danger of premature detonations possibly even turret fires from the spilt powder, already mentioned.. That was cured by adding a compressed Nitrogen (initially) and later a compressed air scavenging system which basically blew all the still burning remnants out the barrel, after a round was fired, before the breech was opened.
There were trials with 76mm, 90mm and 105mm guns and howitzers in place of the 152mm gun/missile launcher but none were proceeded with beyond trial installations and the 152mm gun/missile system was persisted with. When it worked properly, it was a good system but it was hard to maintain and use to that standard. Most rounds fired out the gun were conventional, rather than missiles. Even then, it had a remarkably short barrel life, measured in only 200 rounds because of the massive erosion the "key way" which was used to align the missile in the barrel suffered from the conventional rounds.