One of my friends got a Thunderer in 45 Colt--as this rifle was never designed for the 45 Colt it requires a certain shape bullet for successful loading
He does buy commercially loaded ammo that works and wants me to cast that shape--I CAN'T FIGURE OUT WHAT IT IS!
Pictures show it to the right of a Lee 255 gr RNFP
It is 250 grains and must be coated as there are no lube grooves. Weight could be lower as long a nose matches
Lube grooves or not either would be fine as long as nose matches. I powder coat so grooves are optional
from the pics you can see it has a different radius and smaller meplat