Love the SAFEHOLD novels
folk are correct about the lock should be on other side, however for an artistic design/explanation your image does "work" and is only way you can practically show it as an artist, people forget that!
though the butt would need to be "taller" and have a brass plate, both from practical need and actual book explanation
Butt has to spread the shock of firing, that one is too narrow and would smash your shoulder hard, recoil on a .50 cla black powder rifle like that would be seriously powerful
military rifles had brass butt plates largely because of way they were used in training the old fashioned "square bashing" as the British Army would say (grounding the riflere peatedly would end up wearing the wood) and for fighting
I don't know how they'd do the stock/trigger design, I can't remember if the books say
think a "thumb hole", all in one design is more likely than a pistol grip because an all in one is tougher
or maybe like the Russian "Dragunov" styleimg0.etsystatic.com/114/0/7000…