Why would they reduce capacity if they are actually shorter than 2-3/4"? We have not found this to be true whatsoever in any gun we have tried them in.
Additionally, the S&B slugs are 1350fps minimum. That is faster than many slugs out and only about 16% off the 1600 maximum listed by everyone else. S&B is conservative in their numbers and as they use European measures for opened shells they also conservatively list their ammo as 2-5/8" instead of 2-3/4" (2-6/8")
They are fantastic shooting slugs. They do not reduce capacity whatsoever. They are shorter than 2-3/4" shells by a miniscule amount.