I assume we are talking <2mm? so not much point in "scarfen the edges"?
Typically we scarfen unidirectinal CFRP 1:50, so that would give a 100 mm scarfened overlap.
Depending the exact layup of the barrel the value might be a bit lower, as it for sure is not fully unidirectional.
Some Information from a very old
glider repair handbook (all glassfibre)