13' 7wt. Have been out on still water practicing and gotten 2 lessons from an instructor.
When messing around with casts, I will sometimes do a double snake roll the reset the anchor.
The cast after the snake roll always is the best. I shoot the most line, in a tight loop.
I have no idea why this might be.
I know it is a tricky question but I thought more experienced might have some ideas.
The only sense I can make out of this is you are doing a snake roll without shooting anything, then doing another snake roll the other direction to bring the head 90 degrees back to where you started? Is that what you are doing? Forgive me if I have it all wrong. That would seemingly be a lot of work! But I take this to mean you do whatever you are actually doing just to get set up for the regular cast you do, which works better when you do it beforehand.
Without being able to clearly visualize what you are doing from what you have written there are a few things about “setting up” that will contribute to your success - if you have a sink tip anything that gets it further towards the surface before you start the “real” cast will help - less water friction on the lift.
But most importantly LACK OF SLACK before you start the cast would be a KEY thing for success, and might even be the point where the whole cast starts going wrong due to too much slack! When you first start learning it usually is. So as the instructor may have mentioned you start the tip of the rod before the lift down at the water level pointed downstream at the fly. To minimize slack you can also carefully point the tip and lower it as you strip in from the last cast in effect getting ready for the next cast - if you do it smoothly enough you can keep the line taunt and near the surface right up to the point you start the next cast. Fast moving water where you are standing can help with this. But no matter how careful and/or experienced you are if you are are standing in especially deep and/or slow moving water you may need to reset the line before starting the cast. When practicing in still water like you are doing these pre-cast set-ups are virtually mandatory. The usual way of doing this is a roll cast, even sometimes working up to a switch cast if preferred. Doing switch casts BTW are fundamental in spite of not being a fishing cast in most cases on moving water. You should do lots of them to practice and improve on basic timing.
At any rate these setup procedures will bring the whole line to the surface and if you lower the tip as the forward “cast” comes tight you will be in the ideal configuration, straight and with no slack, to START doing any spey cast. I am assuming without %100 confidence from what you wrote that you are doing a “double snake roll to reset the anchor” to accomplish the same thing. It would help if you explain what you do before each cast when you don’t do this, but my first guess is maybe it just isn't working as well for you at getting things tight before you start. Again, practicing on still water as you are you really have to set up carefully as you are not getting ANY help from the water itself.
But having this help your subsequent cast would make perfect sense for the above reasons. But I’d try rolling it out instead - it replaces all the motions you are doing with the “double snake roll” with just the last stroke of your complicated procedure - the one that really matters. New casters are often encouraged to roll the line out as many times as necessary before every cast as it helps remind them to get in the most efficient setup position. Later on this will become subconscious - thousands of poor and good casts will eventually give you enough muscle and tactile memory that you will just know without too much conscious thought if you need to reset the line before proceeding.
Anyway if I’m reading you right I think this is a good guess at why it is helping - the final result of all the motions leaves you in a nicer place to start with everything under more tension.