I think you did a good job. I would be very careful though. I like how you cut out the groove in the middle for less friction I'm assuming. I use Barnes bullets in my 300wby which are solid copper and they also have multiple grooves in them. Copper is a little softer than brass which would be easier for the barrel rifling to cut into and it would also be less abrasive to the barrel then brass. I don't know about using zinc, I'm not exactly sure about its physical properties but I would think it would be too light or not dense enough. Within 100-200yds probably wouldn't matter too much. You could try doing some research on properties of the best bc bullets. A lot has changed since my spear manual was written but I read that they had the best luck or bc with a bullet that had an ogive radius twice the bullet diameter or something like that. Anyways good luck and be careful developing a load, it's hard to say exactly how well that bullet will move down the barrel