My Immanuel Meffert arrived today. What I bought as a combo gun, a 16ga and a 8.5mm, turned into something better. The 16ga barrel is fully rifled, and from the chamber cast the 8.5 could very well be a .450 BPE. I don't have the case demensions for the 450 BPE. Length is 3.25", case in front of the rim is ~ .555, rim is ~ .623 and the neck is ~ .478, lands are .435 and the grooves are .458. Please take these measurments as approximate only. Making chamber casts isn't what I do best. It's a Jones underlever hammergun with two blade sights, one folding, neither marked for yardage. Set trigger for the rifle, folding peep sight and a trapdoor buttplate for two 16ga shells. It's a shame someone put it away wet. The whole right side is pitted on the outside. Another one to play with.
