I have used them for hunting boar in Australia's tropics, they are devastating within about 30 yds. After that, the pattern spreads a bit and some pellets will probably miss.
On a recent culling trip, I shot a reasonable boar (~80 kg) at about 25yds, all 9 pellets were on the chest area and one penetrated completely and exited. Pattern diameter perhaps 15 inches.
Several of the pigs on
this thread on NE.com were killed with SGs. The gun is a cut-down William Griffiths boxlock, which suffered muzzle damage in a previous life, now true cylinder-bore and regulated for slugs and SG.
...and just to add some colour to
this post, here's a 90 kilo boar which caught 6 out of 9 pellets in the side of the head as it ran past me flat-out at around 18 metres distant. The other 3 probably went just over the forehead. Pattern diameter perhaps 12 inches.