Federal prosecutors in Del Rio say 23-year-old Jesus Cardenas and 34-year-old Luis Cardenas remain in custody pending sentencing this summer.
A jury in Del Rio convicted the New Braunfels siblings on two counts of smuggling ammunition meant for Mexico. Jurors also convicted Jesus Cardenas of two counts of smuggling ammo and magazines.
Federal agents in December 2011 seized part of the ammunition along with 23 assault rifles within yards of the Rio Grande outside Del Rio. More ammo and magazines were confiscated in early 2012.
The brothers, who were convicted Friday night, face prison terms of up to 10 years and maximum $250,000 fines.