WVFred,

No idea about value in the sense of price that you might pay for the rifle but Mahillon is an old and highly respected name from Belgium and on par with Pirotte, Lebeau Courally, Francotte, Dumoulin etc. The company closed down many years ago but the name has been bought by a very prestigious dealer in Bruxelles. I don't know whether they could advise you on your rifle but they have a website http://www.lamaisonduchasseur.com/ and you might try contacting them on e-mail.

Best wishes and please post pictures of your rifle if possible.

Good hunting!