I wouldn't use a TMZ (use a TEZ), the boat tails don't seem to shoot all that well, some have good luck, more don't. From what I have seen, the last 1/8 inch of the bullet will fill the bore, here is a 290gr TEZ (flat base) pulled from my backstop (the bullet is damaged from stone, sand, and dirt). You can see where I knurled the bullet and where the knurling is mostly rubbed out on the last 1/8 inch. A duplex load was used for this bullet along with a .060 veggie wad. I think it would obturate enough with a single powder dose but only one way to find out.