The common philosophy is that a guerilla force requires the occupying force to expend 7X the force to restrain the guerillas. IE, a 300-man guerilla force would need at least 2100 men to contain them. THese men would be guards, patrols, escorts, and platoons searching for the guerillas.
iirc, in WWII the USFIP (US Forces in the Philipines) was a guerilla force led my self-promoted Brig. Gen Wendell Fertig (Formerly Lt Colonel, Reserve Forces). Fertig's forces numbered around 30,000 men, including Fillipinos and escaped US servicemen, and only about 15,000 of them had some sort of firearm. His band of irregulars (About two divisions' worth, scantily equipped) tied down about 300,000 Japanese soldiers, which is an entire army group.
Guerilla forces typically do not need large quantities of materiel because they do not ever intend to get into large scale firefights. A guerilla force's job is to harry, harass, and deny security to the occupying force, reduce morale, and to force the occupying force to expend men and equipment dealing with the guerillas.
Long range accurate rifles, to snipe individual opposing force soldiers, damage equipment, shoot holes in fuel tanks, etc. are much more useful than assault rifles, to a guerilla force.
The calibers you speak of would all have some ammo available, even a bandoleer of rifle ammo would have enough to equip a large number of guerillas. They won't have anywhere to stockpile supplies securely, and have to be highly mobile with what they can carry.