Possible reason it doesn't fit a h&k factory barrel - Griffin Armament Suppressor Alignment Check Rod

This isn't a review but a response to Aaron 1 star 12/11/2022 review. H&K factory barrels have polygonal rifling (hills and valleys) not conventional lands and grooves like majority manufactured barrels. The polygonal shape create a tighter seal for the gas to stay behide the projectile throughout the lenght of the barrel. Which mean a slightly smaller bore diameter, causing the rod not to fit