There's a photo on p. 227 of Lebo's "Godfather Legacy" of five guns laying on FFC's director chair. The caption reads, "Equipment for the director." Presumably one of them was young Vito's gun. But can't I figure out anything else from that photo.
The subject of guns has come up on this board many times in different contexts. It's an area where FFC's fanatical attention to detail and authenticity slips a bit:

Clemenza gives Rocco the right gun to use on Paulie: ".22 snub nose." A .22 has no self defense value because it has little stopping power. But it's an ideal assassination weapon if the shooter knows he can put the muzzle right up against the victim's head--it's small, concealable and quiet. Michael used what appears to be a .38 Special on McCluskey and Tattaglia. That'd be consistent with Clemenza's comment that he wanted the gun to be noisy to discourage "pain in the ass bystanders."

On the other hand, Sonny gets his with Thompson submachine guns. Looks like he took about 50 slugs and continued to pirouette before he finally expired. The Thompson fired .45 ACPs--the proverbial "big slow round," designed for stopping power. In reality, the first bullet that hit him would have killed or disabled him--FFC obviously was paying homage to Arthur Penn's "Bonnie and Clyde" in that scene. He also got carried away in the Great Massacre of 1955 scene. Cicci whacks Cuneo with what appears to be a Colt Model 1911 .45. It'd be too big for him to conceal effectively. And the "big slow round" might have been deflected by the thick safety glass in the revolving door. Rocco and a cohort use Danish Madsen m/50 military submachine guns to dispatch Tattaglia and his hooker, naked and unarmed, from a distance of about six feet. But then poor Neri has to take out Barzini, his bodyguard and chauffeur armed with nothing more than a standard .38 Smith & Wesson six-shot police service revolver.