Greetings,
There are some aftermarket adjustable bars available.
I do not care for them as you spend a lot of time trying to get the perfect powder drop.
Personally, I use a brass bar with a 0.500" hole bored through to accept 1/2" bushings.
I copied the Lee Precision method and size the bushings in CC (cubic centimeter) values.
When I change powder, I look back in my load book to see what bushing I use last.
Cheers,
Dave