Grain Absorption: unheard of amount?

So, I'm currently brewing my first stout, and the grain bill is 13lb. During the mash, I hit all of the right temps and everything, but somehow only lost 1/2 gallon of water due to absorption. Talking over with a homebrew buddy, we came to the conclusion that we have never heard of such a low amount. He made me second guess whether all of the grains were ground, but I'd like to think I have enough sense to not forget that aspect...
Has anyone ever heard of such low absorption amounts, or did I F up along the way? What is a normal amount to lose? My homebrew app defaults at 0.13 gal/lb of grain.

What type of sparge method did you use? Perhaps there was some channeling?

Also, did you use a bag, because its possible to get better results when you use a bag that you can lift out of the mash tun and let gravity force the wort out of the grain.

I just did a single sparge (if that's what you call it). I went along with what my Brew Pal app said to use , amount wise, and mashed with 4.9 gal and spathes with 4.3gal. I just finished the brew process and my gravity wasn't terribly off (estimated 1.058 actually hit 1.063)
No, I did not use a bag, just a home built cooler MLT.

I usually lose around 0.10 gal/lb, but I also have zero deadspace in my MLT and let it drain for a very long time. How are you measuring your volumes? My guess is that you either added more water than you thought or collected less than you thought. A half gallon absorption for 13# of grain just seems way too low to me.

maybe the grain was weighed wrong?

Any dough balls? What was you effeciency like?

13 lbs for a stout also seems like a lot. Was this a double/imperial? If not, maybe your grain bill is off and it wasn't that bad. How big is your MT? How full was it?

it would seem likely that there was a measurement error somewhere, either weighing grain or, more likely, you used more water than you intended.

dough balls, unground grain, etc....i'd only consider those if you ALSO got substantially lower efficiency than typical for your system.

Thanks for the input guys. I am starting to believe I mismeasured my mash water. It would make a lot of sense if I accidentally used an extra gallon.
I used a base recipe I found online. It's actually a chocolate orange stout. I'm not sure what a normal stout grain bill looks like. Hopefully it comes out okay.
Thanks again!