I'm a lot more concerned about there being nothing to support or even guide the middle of the bullet as it first begins to move than I am about having a lube groove poked down into the powder space.
What you have there is what I call a "Lyman manual load", where stuff goes together sorta and works ok at mid-range velocity, but isn't going to do well when pushed at high speed/pressure because there's too much going wrong during the launch. Richard and John Lee would explain this as a compressive strength failure of the alloy, someone else would explain it as exceeding the practical limitations of the rifling twist with cast bullets, and I explain it simply as a failure of fit and balance in the system which results in a non-balanced, non-symmetrical bullet when launched at high speed. It's like putting a 600 HP engine in a Buick Century...it might have the power to do 200 mph on a track, but the suspension and tires quit on the first turn and put you into the wall.