Calculating mash tun dead space

Hi All,

Yet another all-grain newbie here!

So, this past weekend I brewed my first All-Grain batch.  After doing the batch sparge, I ended up with approx 3 litres more wort than Beersmith calculated.  I'm trying to figure out why, and adjust for future...

My mash tun is a square "cooler box" conversion, with a bazooka filter fitted as low down as possible.  When I tested the dead space , I measured the volume to be 3.8 litres.  However, this is obviously when just water is in the bottom of the cooler.  If grain is in there too, wouldn't that be using up some of the volume, along with the water the grain itself has absorbed?  Should I reduce the dead space value in my equipment profile?

Thanks in advance!...

I think I might have got this figured out!  Could someone check my logic?...

My lauter tun loss figure was originally set to 3.8 litres (measured previously with tap water) and grain absorption was left at the default.

In my brew I had 7.35kg of grain and mashed in with 23 litres of water.  I got approx 15 litres as first runnings.  23-15 = 8 litres left in the tun.  7.35kg of grain absorbs about 7.36l, leaving 0.64l unaccounted for in the "dead space" rather than the 3.8 I was expecting.

This would account for why I had around 3 litres extra pre-boil...