Dimples in Magazine Tube of Remington 870

I have received answer about dimples in magazine tube from the first hands, directly from the Remington:

“The dimples in the magazine tube is to keep the new style retainer in place. If the
dimples are removed, the retainer would not stay in place. We do not recommend these
dimples to be removed. This style was introduced in the late 80′s.”

Thanks to the Remington for this information.

But if you want to install magazine extension you still need to drill them out first.