Do you think I can mash this much grain

I've mashed 25#'s of grain in my 10 gallon igloo cooler before.

Do you guys think 28#'s is too ambitious??

Thanks

According to Beersmith if you mash 28# (12.7kg) at 2.3L/kg you need a 38L MLT. Sorry its metric but it will fit.
Ive got the same size MLT. My rule-of-thumb is to add a maximum of 10kg (22#s) grain to mash at a minimum of 2.5L/kg. That means I can make 10 gallons of about 1.060. Anything higher and I either add DME or make 5 gallons instead of 10.

it says 10.99 gallons...

I use that rackers calculator everytime and I fully trust it. It matches up perfectly when I dough in. After mashing for an hour, and doing some recirculation, everything compacts a little so you could maybe sneak a couple pounds in.

Maybe you could try some recirculating in the beginning, then top off with your extra grain at the 30 minute mark? When you add the grain, you might have to continue recirculating to make sure the new grains' starches/sugars get mixed in.