Re-rivetting M1919's and L3's was an everyday occurrence in our workshops, same as the GPMG/L7's The GPMG's were cold rivetted but the M1919's were hot rivetted but....... We'd drill the old loose rivet out taking great care not to touch the shank part of the hole. Get the rivet red hot insert it from inside, anvil bar below and then rivet it tight manually. The best part was that these guns had to be tested in the AA fire and depression mode. That was firing a belt into a depression pit, no tripod.......... just let rip!