GEORGE WALLACE says: Taping the muzzle is a sound idea because it stops rain and any other debris from getting in the bore.
During my days in New Zealand I have known the barrel of a .308 seriously bulged – and therefore ruined – when fired with a tiny piece of bracken in the bore. The owner, a close friend, thought the bullet would push the bracken out.
He was right – but the sudden surge of pressure as the bullet reached the obstruction left a very visible bulge which made the barrel useless.
Received wisdom is that a piece of tape over the barrel will neither affect accuracy nor increase pressure because the column of air ahead of the bullet blows the tape away and allows the bullet to fly normally.
I have tested this theory several times and accuracy appears unaffected.