Effectiveness being the operative word, NO. A pellet has no effectiveness at 450 yds. As light as a pellet is, it would have no energy left. That is not to say it would not/could not cause damage, as noted above, I wouldn't want it to hit my eye. I've been hit by shotgun pellets at less than 200 yds, and while it didn't make me happy, it did not cause serious injury either.
Beeman and all others just want it to be know that a pellet can travel that far, and in extreme circumstances MAY cause damage of some sort.
When I was a boy I took a Red Ryder BB gun and shot at a window of a church that was more than 100 yds away. I did so to prove to the fellow next to me that the BB would go that far. The window cracked, and I spent the entire summer mowing grass and the fall and winter raking and sweeping to pay for an 8" x 10" window glass.
If Beeman tells me that that might happen at 450 yds. I'm going to take their word for it....