Well, the rifle was condemned by a gunsmith as being beyond repair

It looked in good condition but had a couple of burst .22 long shells in a plastic bag attached to the trigger guard, I said it should not be used with anything but .22 Automatic ammo which is hard to come by, so he looks in his ammo store and comes up with a few boxes of Winchester .22 Automatic ammo and asks me if I'll take a look at it

The mag tube was filthy where blow back from the wrong shells had blasted soot everywhere, so a good clean and I thought load her up and let rip, no go, the cartridge cut off was not letting the cartridge go past to chamber but was letting it go far enough to jam the bolt.
Now I don't know much about the 03 but I thought it might be a weak spring in the cartridge cut off. I took it apart and the little spring did feel weak, I cleaned and oiled it but it made no difference.
The rifle fired and ejected fine in single shot mode but jammed if any cartridges were in the mag tube, has anyone here had a similar problem with this model?
Numrich have the spring @$5.20 but are sold out on the cut off.
Any advice would be appreciated.