Just to play devils advocate for a moment.
Could it be that Sierra actually loads up to actual SAAMI pressure limits with their bullets and does not have a few lawyers sitting on the sidelines saying "cut the top load by at least 20%"?
Just thinking out loud since I don't load 44 Mag.
I do know that in 357 Mag, 357 Sig and 357 Maximum that if you follow the Sierra book exactly, work up from their starting load with no substitutions of any kind, that in my guns, I see no pressure signs.
Now, substitute this, change that, modify this, all of a sudden Sierra's loads can get hot quick and show pressure signs.
So as usual, ArchAngelCD is right.