Hi, if it is original butt, there should be a steel butt plate on there with a small trap door, if you open that the stock bolt should be accessible, some times there is a leather washer in there that buggers you up, so shine a flash light down there to see, you need a big long handled screw driver or slotted end on a socket wrench to tighten .

Now this is Ok if it is a early Speeder on the MLM-MLE action, if it is on the later SMLE MKIII action there is a steel insert in the fore end wood so you must take the fore wood off BEFORE trying to tighten or you could crack the fore wood !