If the barrel ran 80% of the length like that then the shroud would not be very effective. The shorter the barrel, the more shroud volume you need for equivalent noise control. In some cases length can be reduced by increasing diameter but it doesn't look like there is much clearance room for it there.
if you don't care about keeping it quiet then just remove the shroud and reduce length like that.
I know you want to shorten it without compromising on anything else but you can't so you just need to decide what is most important to you.
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