Sanity Check with mash volume

I don't understand this...

First time brewing a 5-gallon recipe and had an issue with mash volume calculations. My mash tun is a 5-gallon brew kettle. My Christmas Weizenbock calls for 12.25 lbs of grain:

6.5 lbs Pale wheat
3 lbs Munich
1.5 lbs Maris Otter
0.75 lbs Vienna
0.5 lbs Crystal 120

Based on Green Bay Rackers "Can I mash it" calculator, mash volume @ 1.25 qts per lb thickness calculated to 4.81 gallons, which is very close to my mash tun capacity of 5 gal (with no dead space).

BrewCipher (and a later manual calculation) calculated a strike water volume of 3.83 gals. After accounting for the 0.32 gal / lb of grain, the numbers agreed with the "Can I mash it" calculator of 4.81 gal. I didn't really think too much about the strike water volume until I added three gallons into my tun. I looked at my sack of grains, looked at the remaining space in the tun... and thought "no freakin' way it's all going to fit".

I doughed-in at 3-gallons, which brought the mash close to the top of the tun, and added another qt of water (total 3.25 gal) and decided that the remaining 1/2 gallon was simply not going to fit (1/2 gallon takes up 1" of space in my tun). I was already about 3/8 inch from the rim of the tun.

So what gives? Why doesn't this calculation appear to work?
Anyone else run into issues with the calculations? I'm pretty confident in the volume of my tun... but I may just measure it again to show I'm not going insane.

 

Hmmm... some valid thoughts... most of these I think most people would assume (myself included) are correct, so good to challenge!

At my LHBS, I watched as the person helping me weighed out the grains, and it was 12.25 lbs. Have to trust the scale was accurate, or they are giving it away.

Grains were fully saturated

I was using one-gallon jugs of bottled water (my well water tastes crappy) and the last 3 quarts were measured by hand,

Leading culprit is assumed 5-gal volume of SS pot. I will confirm this first chance I get,

Thanks!

 

That's the question. The accepted wisdom is that a pound of saturated grain occupies a volume of 0.32 quarts. Grain volume should be 3.92 qts or 0.92 gal. Total volume should be 15.3125 qts (water) + 3.92 qts (saturated grain) = 4.81 gal, which is what calculators calculate.

This overflowed my (assumed) 5-gallon tun, and it is appearing more than likely that my 5-gallon tun... ain't!

I will measure it tonight and post the awful truth.

 

I've seen this before and it is cool! My new Bayou Classic kettle is already stamped with gradations... but to be honest, I don't believe the markings. They don't add up with measured volumes I've added in when testing boil-off rates with the new kettle.

 

The tale of the tape(measure)....

After carefully measuring up my kettle and calculating the volume, I find that, much to my chagrin, it ain't no stinkin' 5-gallon kettle. Actual volume is approximately 4.7 gallons, which goes a long way in explaining my predicament. Dammit! Now I need a real mash tun that I can apply heat to for step mashing. I like my new Bayou Classic 8-gal kettle; may have to ask for another one for my birthday for a mash tun!

Oh well... I guess this officially puts me on the path of building a RIMS system down the line

 

I'm actually relieved that the cause of my issue is an undersized kettle. I mean, if you can't trust a model, then you might as well be guessing. I'll certainly be keeping a closer watch on my mash volumes for a while and cross checking against BrewCipher and Can I Mash It.