I just did my 9th all grain today. Up until the last 4 batches I used the LBS grain mill for the crush. I have gotten between 68-73% efficiency. After I used my own corona mill the first 2 batches were the same but the last two were over 80. Now the only difference with the last 2 was mash time. I got stuck in traffic and ran late on last weeks brew. It mashed for 2 1/2 hrs and I got 81.5% efficiency. Today I figured let me see if this works again and did a 90 minute mash. Well I got the same 81% efficiency today. I thought conversion should be done around 60 minutes. I did a search and came up with people talking about a 20 minute mash? Im kind of confused and will end up with a stronger brew which is ok but if I can use less grains great. Oh also all mash temps were between 150-153 for all the brews so I dont think this had a big effect on the efficiency. Thoughts .