Detlef, thank you for sharing these very attractive knives, as well as for the perfect descriptions and excellent photography with details.
While I know very little on the weapons of SE Asia, I have always found the esoterica most interesting, so am looking forward to learning more on these as well.
Meanwhile I have taken some time to discover what I can, with emphasis on trying to confirm if these are indeed shamanic implements as suggested. It would seem of course quite likely as they are not sharpened, and it seems the antlers are something often associated with shamanic ritual .
Interestingly, I have seen American Indian knives using antlers in this manner for hilts, and it seems they were associated with chiefs or medicine men (indeed shamanic). I also recall from a book titled "The Mind in the Cave" discussion on shamans, and cave art images from France which showed prehistoric shamans wearing antlers . From anthropological POV it is fascinating to see these kinds of symbolic elements transmitted through so many cultures.
It would seem that Tonkin (North Vietnam) tribes may well be the provenance for these but clearly they could be from various tribes and regions throughout these SE Asian areas. Apparently the animist beliefs and rituals in Vietnam became absorbed into those of Buddhism, Confucianism and Taoism, and it is indicated that most of the shamanist duties were taken over by Buddhist priests ( "Lost Fighting Arts of Vietnam", Haha Lung, 2006) with the arrival of Chinese culture .
It may be presumed that these knives were used as ritual implements in much the same manner as the 'phurbu' (often termed 'ghost dagger') in Tibetan Buddhist ritual. These implements are used symbolically against malevolent forces and demons .
I found this link to 'Shamanic Arts of Vietnam' and possibly this site might offer more inroads into whether these actually are Vietnamese shamanic implements .
http://www.54traditions.com.vn/index...d=10&Itemid=15
Looking forward to more from others on these very nice acquisitions!