Follicle size, ovulation and gravid

Just a couple of questions here. What size follicles have most of you found right before ovulation? I know it varies but I am curious to see what others have found as a general rule. From early ultrasounding, dates and palpation I feel its around the 40-45mm? I have missed many ovulation so can't be too certain. I have girls with follicles around the 45mm mark that are in shed so I can only presume its a pre-lay shed. I do however have ones that have smaller follicles that are in shed. These shed not too long back so this is whats confusing me about the follicle size. Also what sort of point after ovulation do you tend to feel that 'hard' belly where palpation of eggs can't be done? A couple of girls are doing this and a couple aren't. I feel they have all ovulated. Any comments would be great here as I think it would help many.
Paul