I just recently learned that you can still buy the MK1 style HW97 brand new, minus the 25mm internals of course. An outfit in Germany still stocks them, current production. And in a combination of about any current Weihrauch stock/action combo. 

Haven't had a 97k in a long time, I need to pick one up again here soon. Got a few 77Ks, but no 97K. 

Helluva nice collection you got there Mike! 
 
What scope & rings do you have mounted on the rifle in the bottom picture & thanks.

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That was a Taiwan Bushnell Trophy 4-12x40mm scope I bought used off ebay. The rings I got off ebay as well. Don't know the brand. But they work great. 
 
Guys have been doing this for years with a variety of materials. The synthetic stocks are hollow and act like an echo chamber right into ear, many like myself find it unpleasant. Anything from expanding insulation foam to Playdough and even rags have been put into the 2 chambers underneath the recoil pad. I wanted sound deadening as well as added weight at the rear so I went for a combination of gun cabinet foam liners and duct seal. This combo worked well for me and I would recommend it for anyone to try, it is cheap and easily modified or removed.