There is a knurled, flat tab on the side of the inner mag tube (loading tube) near the business end (loading end). Put your thumb on that tab and slide it all the way toward the end of the tube that would be under the barrel muzzle when the tube is in place. When the spring reaches maximum compression that thumb tab assembly will lock under a spring loaded hook. Load your cartridges into the mag tube, then slide the mag tube into position under the barrel and when the mag tube with cartridges is within a half to three quarter inch of it's home position the hook that retains the mag spring will automatically be released, loading the cartridges against the cartridge elevator in the receiver.
