CLAY SHOOTING
John Bidwell
As you say, it’s not a common sight but, then again, it’s not unusual either – the tape is there to hold a flattened bit of lead in place to balance the barrels.

A double-barrelled gun is usually balanced by adding (or removing) weight to the stock but placing lead under the barrel is a ploy normally used by people who shoot single semi-autos.

From what I’ve seen it’s an effective method of achieving handling dynamics that suit the user’s clay shooting discipline.