Kudos to the folks who correctly identified the subject of Muzzle Blasts Pt. VI as a Garand, better known as the U.S. Rifle Caliber .30 M1. It's pretty hard to mistake the profile of the M1 Garand, with the gas system sitting so close to the muzzle, and the gas tube right there out in front for all to see.
Here's a better view of same, doing a wonderful job of sending 168gr MatchKings into nice groups at the rifle range:
For the next unknown muzzle, I give you a rarity, although the origin should be visible when viewed in finer detail: