The bushes on my two T8s don't touch the barrel at all.
This is apparently to allow consitent fitting of the mod based on the shoulder of the thread, rather than on a blue-stripping touch-fit of plastic on steel at the rear bush.
The gap ain't large, so the bush wil still take the strain off the thread if the mod gets a knock: which is, I think, the point of it. The T8 is very long, so a knock near the back gives quite a wrench to the thread - to be avoided especially if they're on 1/2"unf, as mine are.
The Northstar is bushless, but much shorter. Furthermore, mine is robustly arranged on a M17x1 thread with a 1" spigot.