Sorry, but I don't see what is so hard to understand, the top edge of the lower receiver on the rollmark side has been sanded too hard and is only half the thickness it should be so it doesn't match up with the upper. I understand it doesn't affect the usefulness of the lower, but when I read BCM's ad's talking about their quality I expect their fit and finish to be better than that of a gun I can buy for half the price, it isn't (and before anybody goes off, I realize there are differences in specs between a $500 gun and a $1000 gun). I did talk to BCM and they told me they were sorry I wasn't happy with the lower, but that it was within their specs and that they would not do anything about. I just thought others should know that you don't always get what you pay for.