It’s a good idea to clean the gun to remove any manufactures oils or grease before shooting it.... I have always taken my rifles apart and have never had an issue with the torque on screws. I usually tighten the till the screws are nice and snug .

I have the .17hmr bore snake and I never remove the wire bristle. The bristle are there for a reason and that’s to clean the barrel.

I’m not sure if the Marlin 917v is a bolt action but if it is you can bore sight your rifle by removing the bolt from the rifle and resting the rifle on some sort of stable rest if you don’t have any maintenance center. Pick a target looking thru the barrel at a certain distance and check where the cross hairs are located. If it’s not close dial them in as best as possible. This should help in sighting in the rifle and put it on the paper as long as you’re not starting to sigh in at 100 yards. I would suggest to start at 25 yards.

I also have some Hornady .17 with greyish to blackish tips. I don’t see that being a problem. I think it’s just some kind of coating to stop the bullets from tarnishing..... Good luck with your new rifle.