Seed beads are essentially spherical in shape. Wampum is cylindrical with straight sides. Typically, Wampum beads will be bigger in length than in diameter.
This is an example of seed beads. These are roughly 8/0 in size. They are what we would call "pound bead" or "pony bead" size. It's what we see on decorative beadwork on clothing and other household items. This is what I believe was used to decorate these guns.
Pre-contact Wampum was made from the channeled whelk shell or quahog clam shells. It was either white or purple in color. Europeans later introduced copies made in glass. Here are examples...
Wampum beads weren't used on daily items. They were used on items like the Hiawatha Belt, and on similar belts used in political negotiations.
Applying a wampum bead to a gun stock would require a fairly deep hole. And all the beads would show the hole exposed at the wood surface. A study of these guns shows beads sitting at all different angles. In some cases you see the hole... in some cases you see the side of the bead.
Believe it... or don't believe it... these are seed beads.
P.S.
Trading post gunsmiths were sometimes tasked with adding brass tacks to Indian guns. I believe they also could have applied bead decoration.
Oh... and I found that article. It was in the January/February 1995 issue of Muzzleloader. I had the author wrong. It was written by John Stovall.