If all else fails this will work. The rifle forend nosecap, if its an original or a proper copy, will be machined to take this kind of collar (I think its how the "button" short magazine tubes were retained)
Picture is a 92 but I have done the same mod on my uberti 76 rifle - collar does not need to protrude out of the nosecap like this one - I was taking up some windage in an old nosecap I retrieved for this rebuild
so the collar once it is fitted up properly is silver soldered to the tube and engages the machined groove in the nosecap.
assembly is not as easy as before but ok so long as the tube will slide easily through the front retaining band --