Thanks mate, that looks like the best option for now. I suspect that if I try getting the barrel out of the block I'll end up making a hash of it, especially given the ambiguity about how it may be fixed.
Of course that does completely invalidate the silencer I bought for it () but hopefully if I sell that on here I can offset the cost of the new sight.
Incidentally is the AA rear diopter any good on springers?