I am a trained Armorer in S&W revolvers, semi-auto pistols, Sig pistols and Colt AR-15/M-16. Just a small part of my job. LE agencies rarely have full time armorers at modern pistols do not require all that much attention. The larger agencies (NYPD) may have had full timers when they had 30,000 revolvers in service.
Military is a different story. Larger installations have armorers that work on guns regularly, but much of their job is not very demanding. It is tearing down worn guns and replacing parts.