Do you mean the gun sleeve? It’s made of three segments, but you have to look very closely to see the two fine grooves separating them. On the Trumpeter barrel these are much too pronounced (and the tube is too short by 3mm). If you look closely the turned aluminium barrel from Magic Models seen in the picture above has them.
The kit part also has a collar on the end of the barrel, which wasn’t present on the KV “large turret”.
It’s a shame the replacement barrels from Magic Models are so hard to get these days. The ones from Aber are also fine, but they require much more surgery.