Armadale Detectives officer in charge Ray Horne said early on March 8 police found 15 grams of bagged methylamphetamine, smoking implements and 40 rounds of .22 calibre ammunition in a sedan they stopped on Champion Drive in Seville Grove.
He said police arrested the two young men occupants and seized the car.
Senior Sergeant Horne said detectives later executed a search warrant at a Seville Grove home, and found a .22 calibre unlicensed handgun, crossbow, five cannabis plants growing hydroponically, more drug paraphernalia and ammunition.
A 25-year-old man is due to appear at Armadale Magistrates Court on April 5 on weapon and drugs-related charges.
Sgt Horne said two days later at Bentley Liquor Store on Hillview Terrace a man allegedly produced a 30cm kitchen knife from his waistband, pointed it at the 29-year-old woman behind the counter, and took bottles from a shelf.
He said responding police found a man in nearby Dumond Street, allegedly with the knife.
Armadale Detectives later charged a 22-year-old with armed robbery.
He appeared in Perth Magistrates Court on March 11 and was remanded to appear again at Stirling Gardens Magistrates Court on March 20.