Not completely true. The Chicago Typewriter and IRL have infinite ammo and the Handcannon also has infinite ammo, if you buy the Exclusive upgrade (790,000ptas).
If you're a good shot, you can use the CT to free Ashley from the wall straps. Just aim to the left of her body and when the laser gives a clean dot on a strap, fire one shot. Just tap the 'A' button lightly to get single-shot from the CT. I never use the rifle for that any more.