The F1 is a simple blowback design firing from an open bolt with a fixed firing pin. It shares many design features with the British Sterling submachine gun. Unlike both the Sterling and its predecessor, the Owen, the F1 has a removable wooden butt and pistol grip. A curved, detachable 34-round box magazine is inserted in a magazine housing on top of the barrel, similar to the earlier Owen gun. The top-mounted magazine is unobtrusive for carry and when lying prone. Lightning fast magazine changes can be mad;, it has the added advantage of only needing a light spring being no harder to load than a .22 magazine not requiring special mag fillers like its contemporaries and to be less likely to jam than a bottom mounted magazine. The ejection port is directly under the magazine and provides a trap for the unwary user; should the user's hand stray back to the port, the bolt moving forwards will 'bite' the web of the hand. The butt-plate and pistol-grip are identical to those on the L1A1 SLR as well as the capability of adapting SLR bayonets.
The trigger is a two-stage pull, half back semi auto, pull and hold back gives full auto requiring a safety catch only easily operated by the thumb. There is a small guard fitted forward of the ejection port to protect the forward hand. The left-mounted cocking handle has a tab that, when pressed, locks into the bolt, enabling it to be worked backwards and forwards to clear fouling. The pistol grip with internal parts came from the production line of the SLR L1A1 rifle, at the Lithgow factory. The wooden butt also was from the SLR production line, reducing the amount of tooling.
Stripping is simple: Safety on, remove magazine, cock and hold bolt open, rotate to left, inspect bolt face and chamber, release bolt under control. Then grab butt, press catch on bottom of receiver with other hand rotate butt to left 90 degree pull off, remove spring, release safety tip barrel up pull trigger bolt slides out. Assemble in reverse. Suggested ranges for use were 25 meters from the hip snap shooting 100 meters using sights.
Because of the vertical magazine the sights of the F1 were offset to the right of the weapon requiring a slight head tilt to the right, the rear sight being a roughly triangular asymmetrical metal flap with a round aperture, the front sight being a blade mounted on the right side of the weapon's magazine well.