The Impossible Planet (1) - S2-E11
Corrected entry: The weapons carried by the security officers are contemporary P90 submachine guns first introduced in 1994, and more commonly seen on the Stargate SG-1 and Stargate Atlantis series. Yet "The Impossible Planet" and "The Satan Pit" are set in "43K" (presumably the year 43,000). It seems unlikely that such (by then) ancient 20th-century weapons would still be in use so far into the future.
Correction: Perhaps the design has proved popular throughout the years or the manufactures have made improvements to the overall weapon without changing its basic shape (if you notice, the barrel of the P90 is longer than normally seen on this weapon).