Felix,
You said "I have a friend who has a merkel he has lead in stock."
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Yes, of course, you will find that on many modern double rifles; it is an indication that the action was made too small, too light in weight, resulting in barrels being made too heavy, to get "recoil control weight", so to counteract that, lead, or mercury recoil reducer, was stuck in the buttstock. YOU WON'T FIND LEAD IN THE STOCKS OF ANY OF THE GREAT OLD CLASSIC BRITISH DOUBLE RIFLES that were made proper and correct weight from the "get go," which many of the modern makers are just beginning to learn from---(Heym, for example, with their latest large frame action model).