I've been using masking tap for years.
After much testing the tan color's masking tape is preferred over the blue.
One fella wraps some tape around the barrel behind the muzzle as a ready supply.
For my rifle with a Holland and DE brakes I've been using fingers cut from surgical gloves.
Balloons are a bit distractive in that they expand before they blow and leave you with a false sense of 'red mist', if you use a red one.
I have some drop charts work up I'll do some experimenting. I think that with the masking tape covering the muzzle only that the bullet never touches it before the pressure ahead of the bullet pushed it away.