imho, buckshot is a short range possiblity that dont work adequate over 25 yards. buy yourself buchshot and slugs and try them on different distances and you will know what I mean.

if you have an pre war drilling in 16 ga chance is very high that it have a 65mm/2,5" long chamber. RWS load the brennecke classic slug also in a special 67,5mm long plastic case thats intended for the old 65 mm long chambers. it can also fired without problems in gun with 70mm /2 3/4" long chambers.