Varying mash efficinecies
[edit: sorry for title typo, and afer talking to others I figured that I am correct in my assumption]
I figure this has been covered somewhat before, but wanted to get some opinions.
I did two 5-gallon all grain batches this weekend. I got different efficiencies, and trying to figure out the root-cause. I have some theories, but would like some opinions.
Saturday I did a 13.5lb batch, 1.25qt/lb, with a 60min mash at 155 degrees. I used my refractometer and from charts I found online it seems I got about a 60% conversion efficiency. The final efficiency was 60% as well (double sparge, hit target temps).
Sunday I did 11.5lb batch, 1.25qt/lb again, with a 60min mash at 150. Used the refractometer again, showed a 75% conversion efficiency, and that tracked through the rest of the brew day as well.
The only variation I had between the 2 batches were different water source (tap vs well), mash temp (150 vs 156), grains used, and what I think is the most important, the brew shop that the grain got milled at (More Beer vs 7 Bridges).
The batch I did on Saturday I had done before, same method, but last time I got 70% efficiency instead of 60% (was my 2nd all grain) and the grains were from 7 Bridges, second was from More Beer.
Is it good to figure that I am not getting as good a crush from More Beer than I am at 7 Bridges? I have gotten varying efficiencies from More Beer, but that is because I use their store mill that can be unfortunately messed with by a customer that "knows what he is doing", and I tend to get intact husks with not fully pulverized grain, while at 7 Bridges the grain seems to have been crushed up finer.
Not a strike at More Beer, their stuff is great, and buying more grain from there is cheaper than getting it at the organic brew shop, just trying to figure out if this makes sense that it is not entirely my fault.