Alex, the available evidence suggests that Winchester and Rock-Ola used spring tubes until mid 1943 and that Quality Hardware used them throughout their entire production. You have to keep an open mind however, as due to the urgency of wartime production, manufacturers sometimes helped each other out with parts, so it could be that you will find a spring tube on a Carbine made by someone else, for example, if Winchester sent Inland some spring tube receivers. These are the S/N's that the evidence available suggests Winchester and Rock-Ola were at in mid 1943. ESTIMATIONS/Not CONCLUSIVE.
Winchester : June 43 : 1115501 - 114180X
Rock-Ola : June 43 : To - 1672000
As with everything about the Carbine, nothing is 100% clear and it is only by sharing info like we are doing here, that we will be able to learn more. Mike.