I replaced my hinge and take down pins with Colt pins. Didn't change the upper to lower fit at all. I was able to swap out the takedown pin without removing the castle nut. I posted about it here last year.
Replaced my takedown and hinge pins without removing castle nut
Bumping an old thread, Installed the V7 Titanium take down pins in my MR556 Lower / 416 Upper and it has a nasty rattle. The pins are of good quality and DLC coated but fitment is not so good with the HK, So cross those off your list of potential choices.
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