I've never hunted elk with a muzzleloader. A couple years ago, a person asked me what pure lead projectile I would recommend to them for elk (perhaps he was in the same type of State requirements youfaced). Not really knowing too much about elk and how they react, but knowing the kind of rifle he owned (since I owned the same one) I recommended a Buffalo Bullet 375 grain SSB. He took my recommendation and discovered like my rifle it shot excellent with 110 grains of Triple Se7en 2f. He later reported to me he was able to shoot a large cow at 80 yards with that load, broadside behind the front shoulder through the boiler room. She walked about 20 steps and just laid down he said. He found the bullet against the skin on the other side of the animal.

Back to your question. I do think that if you placed that bullet in the right place it should achieve the necessary penetration to hit the vitals, expand, and do the damage necessary. I am sure you would not get pass through, but you should get the penetration needed. Especially since you have an accurate load. Shot placement as you know is critical. I am suggesting this because elk have been harvested with simple roundball. Roundball have no where near the ballistics of your projectile. Yet they are able to penetrate, enter the vitals, and do the necessary damage to dispatch the animal. I see no reason why your 300 grain pure lead bullet would not have similar results. Again, I have not shot a elk with a muzzleloader, but have tested numerous all lead projectiles here at the house. They always seem to have good down range energy, and expansion. Good luck, you have a great rifle there... And welcome to the forum. Its great having you here.