Origins
1) Given that the Mark placement for Reign is very specific:
1a) Can Marks of Control intersect?
1b) Are there any ill effects if they do?
2) With the idea in mind that other players may eventually make their own magic, I'd encourage you to change the wording from Reign having two marks of control to Reign's mark of control having two halves. Otherwise, future players may want multi-part Marks that may be less restrained than this.
3) Lefty question: Any question this can't be reversed? Left-handed practitioners would be at a disadvantage; they'll have to learn to aim/shoot with their right hand.
Initiatoin
4) Rather than saying "many initiates die from Reign" I'd encourage you to say "there's a danger of arterial hemorrhage, internal bleeding" etc. Both because it's a new magic (so there aren't many initiates just yet!) and because it sets people up to RP their initiation with medical supplies on-hand, which I think could be neat. Like setting up a little field hospital before they get initiated.
Abilties
5) I believe some formatting for each weapon listed out in Amass (italicizing, perhaps) will make the text read more legibly.
6) Do any of these guns have weight? Do people have to be physically strong to wield them? Can they be used if someone's arms are restrained?
Balance
My reading of Reign's abilities would mean that the following would be true. Please let me know if you agree/disagree with any of these:
A) Reign's bullets would be stopped by Oath's barriers
B) Reign's bullets would be redirected by Divide's Lightning Rod
C) The effects of Reign's bullets could be purged with Baptism's Baptism (could Reign's bullets themselves be purged? I am unsure -- please lmk your thoughts!)
D) Reign's bullets could be Galvanized by Brand practitioners (I think?), as well as Disbanded. Reign's weapons could potentially be disbanded, as well (I think?)
Let me know if I missed any other magical interactions that you think are noteworthy.
Overall: Fantastic job. I'd like answers to these questions, but I don't think it really needs much/any revision.