Not the best of weapons I'll grant, the Italians weren't particularly known for being great gun smiths but since a carbine is a lighter rifle originally meant to be carried by mounted troops it would do the job. Oswald wasn't going for distance here. He just need a weapon with enough punch at a short distance to do the job. In addition buying it through the mail with a false name was a simple way for a simpleton like him to get the gun under the cover of anonymity.
The carbine barrel was short and a round nose FMJ bullet indicates military surplus ammunition. It was old surplus ammunition. Countries dropped round nose for spitzer rounds by WW I. The combination guarantees less accuracy. He would have been lucky to hit the car.