Commenting on the presence of sickle swords (cf. BOM scimitar or “cimeters”) during the time of Joshua (before the time of Lehi et al.), we read the following in the Anchor Yale Bible Dictionary:
Various types of sword were developed in the ANE for different purposes: (1) the sickle sword whose convex edge was sharp and intended for striking (Josh 10:28–39) . . .(Fretz, M. J. (1992). Weapons and Implements of Warfare. In D. N. Freedman (Ed.), The Anchor Yale Bible Dictionary (Vol. 6, p. 894). New York: Doubleday.)
The presence of such in the Book of Mormon (Enos 1:20; Alma 27:29; 44:8) is not an anachronism.
For more, see the following from Matthew Roper: