Mashing in a 50qt Cooler - Limitations?

I have one of those igloo ice cube 50qt coolers that I have turned into a mash tun. I'm planning a big brew soon and I'm wondering what are the limitations on the mash tun so I don't run into issues.

My recipe for 10 gallons of blackIPA is calling for 31.5 lb of grain. According to rackers, at 1.25 qt/lb, that is going to take up 49.44qt in the cooler, leaving me with about half a gallon of space. Is that enough? Is the cooler truly 50qt inside? Or should I thicken the mash up to 1 qt/lb to be safe (that only takes up about 42 qt)? Maybe a volume somewhere between.

Note: I batch sparge so don't need room for a fly sparge arm or anything.

I found that when I followed the racker's calculator for my 10 gallon batch, I used 22 pounds of grain and 1.25 quarts per pound the calculator said it would take 8.64 gallons of space. Well, it was filled right to the top. Not an inch of space to spare in my 10 gallon Gott. The calculator can't take the space under the false bottom into account. If you have a manifold, your volume will be different than with a false bottom.

My MLT is different, of course, but I think that you will not be able to fit the 1.25 quarts/pound in your MLT if the calculator says you need 49.44 quarts of space.

I remember reading elsewheres that 32 lbs is about the limit for that mash tun. I have the same but have never done anything that big. Start with 1 qt/lb, you can always add more later! Good luck and report back please!

Yeah. I think I'll start at 1qt/lb. If it gets stuck I can add water to it to loosen it up.

Yea brian, if in doubt, i would mash thick and infuse hot (boiling) to get it running. Might take 3 batch sparges or so. Raise the grain bed temp near but not exceeding 170.