Day of the Jackal

[BlackIce_GTS]

The book doesn't say either, just somewhere between .22 and .300 Remington.
The 'explosive' rounds (I don't think they're described in the movie) have a hollow partially filled with mercury. On impact, the mercury's inertia hitting the front of the hollow is supposed to split open/fragment the bullet inside the target. I've never heard of that before, but it sounds like it should work. Maybe.

[oddjob]

After reviewing the movie about a dozen times I figured it out. Its a 22 mag.