The Miller artwork shows "tack" sheaths but the problem is what were the tacks? Were they brass tacks with square shanks- such were trade goods dating back to the period. There are however sheaths with lead "tacks" made from perhaps balls or left over sprue material. Some of these sheaths are reported to have been carried by mountain men. There were also harness rivets available pre-1840.
Brasss tacks were probably used if available and lead used on the trail. If you use a round ball, and file it down, the "tack" has a round head that looks great. To keep the head in a round shape make a dished out surface in a wood board to support the round head while hammering the other side. The only trouble is this looks great but may not be PC.
The lead rivets I have seen in photographs are usually flat, probably the top of a sprue, the pointed or cone end of the sprue was likely filed down a bit, stuck through a hole in the leather, and peen hammerred in back. I think if you make lead rivets in that manner you will be more PC than trying to have a perfectly rounded head.
BTW- on some of the original sheaths the lead rivets (flat surface) seem to have slightly different diameters which would indicate something other than the sprue was used. Lead bars were carried at the time and a knife could have been used to chop out lead "nails" that were then used for the rivets. That sounds like what you did and you probably have something very close to the original.
