Glock cautions against using lead bullets in their 45 because the polygon rifling is prone to excessive leading.
I think people are mistakenly assuming the Ultragon rifling is a true polygonal rifling. If their diagram is accurate it is not polygonal rifling at all, it still has lands and groves with a less sharp transition between them. Nowhere has H&R/NEF stated that this is a polygonal rifling, it has been referred to as being "similar to parabolic rifling" by them. Only people here have been calling it polygonal rifling. I would say it is somewhere in between polygonal and traditional rifling, leaning heavily at the later. Just go take a look at the 2008 H&R/NEF Catalog, Page 7, look at the "NEW FEATURE" diagram of the Ultragon rifling as compared to Conventional rifling. Not much different except for the transition between the lands and grooves being at about a 45 degree angle instead of a right angle. I surely is not depicted as being rounded like the polygonal rifling being referred to here.
I have been shooting slug guns for about 35 years, rifled slug guns for 20 years. I have shot nearly every slug made, never had a problem shooting even soft lead slugs in a rifled bore, except for a little extra elbow grease to remove leading after several rounds. I surely don't see any problem here and unless H&R/NEF stamps "NOT FOR FOSTER SLUGS" on the barrel I don't for see any problems.
Glocks shave lead off due to the sharp transition from chamber to the polygonal rifling, I think that is where that problem lies.
This is what polygonal rifling looks like to me on the right, traditional rifling on the left.
Check out the diagram on page 7. Doesn't resemble polygonal rifling to me.
http://www.hr1871.com/Support/HR_2008_Catalog.pdf