17.2%?!? That led me down the rabbit hole to find out beers with very high alcohol content. Apparently Brewmeister Snake Venom, at ABV 67.5%, is the highest.
The highest you will see actually fermented is usually around 18-20%, but there are specialty yeasts that can get up to 25%. Then you can get even higher with extended aging in spirit barrels where some ABV is picked up by absorbing residual spirit as well as evaporation increasing the strength. Sam Adams Utopias for example comes in at 28%
The grain to strike water ratio changes so much that lautering often gets “stuck” due to the thick consistency of the grain bed.
The issue is yield and lautering. The mash is so thick, or rather there's so much of it, that proceses need to be adjusted to account for that, and from experience yields are much lower in a typical entry level craft brewing system (400L).
In the US I think it is technically illegal to make with a brewers license, though some breweries may make an Eisbock and sort of fly under the radar.
Something like Utopias by Sam Adams is 28%, and even at that point, you drink it more like a liquor than a beer.