How do I estimate the shot volume?

Two ways:

1) Dots: approximate as a spherical cap or cylinder (pi*r^2*h). A 1 mm diameter, 0.3 mm high dot is about 0.00024 mL.

2) Beads: cross-section x length. A 0.5 mm wide, 0.2 mm high bead is about 0.01 mL per 100 mm.

Multiply the volume by fluid density for mass: most structural adhesives are 1.0-1.6 g/cm3, so 0.01 mL is roughly 10-16 mg.

These are theoretical values; fluid flow behaviour, substrate and path all matter, so confirm with a sample trial.