There's meant to be on at the 'Citadel of Dinant' never been there so can't comment.
Even 15 years ago they would only display 1/3 of their collection at the Liege arms Museum, the other 2/3 would be up in the loft.
The thing that might be worthwhile to see are the various military/arms fairs.
Some are strictly military some a combination of both.
If military arms are of interest, Armurerie du Nord is a must visit.
You could also knock on the door of the Liege gunmakers school, I doubt they would turn you away and try and do a tour of the various gunshops.
There are also various 'Battle of the Bulge' museums but none I would recommend. Most are quite small considering the distance you would have to drive to get to them.
