Quick is right about guns changing weight...
The 12 gauge Ultra-Slug I used to own had the rarely seen "Variable Weight" option. At the start of shooting hours it weighed 8 lbs by mid morning it was up to a solid 10lbs, by late afternoon a good 14, and by 30 minutes after sunset it was at least 20. Not seeing any deer only speeds up the process.
Now that I think about it, variable weight is probably standard with the Ultra Slug.