Since people seem a bit all over on MH debuts here's some figures going back:
Famitsu 1st week (tracked packaged sellthrough)
MHP3: 2,146,647
MH4: 1,875,115
MHX: 1,542,104
MHW: 1,350,412
Famitsu 1st month (estimated digital sellthrough)
MH4: 225,324 (2 weeks, 2 days)
MHX: 111,554 (2 days)
MHW: 652,614 (3 days from release or 5 weeks, 3 days from hardware bundle)
Capcom IR (official packaged sell-in + digital sellthrough)
MHP3: over 2,000,000 (6 days)
MH4: over 2,000,000 (4 days)
MHX: over 2,000,000 (6 days)
MHW: over 5,000,000 worldwide (4 days)