Your barrel is a commercial target barrel with a front sight block. The commercial block is soldered in place and can be removed by heating the sleeve with a propane torch and when at temperature gently tap free with a piece of brass. Clean the bore after removal so the bore does not corrode. Done several of these. The L42 uses a No4 sight block that you need to bore to the barrel OD. It soft solders in place - alignment is tricky. Not a job for the "faint of heart". Ron (Canadaicon).