i am looking to buy a light oil ball to use when the lanes are pretty much gone. I currently use my nomad solid and move in but sometimes when the lanes become fried i hang corner pins. Was thinking of a fast, maybe wait to see if roto replaces the mars, or what does anyone think of an ultra sonic. I have the availability to buy one but am unsure of this ball.

The Fast is not hugely different from the Nomad Pearl, maybe handling barely slightly less oil, with a similar, but not identical basic skid/flip backend.

The Mars is RG"s current ball for this position. It is a solid/pearl combo. You can drill it stronger with a 3.5 - 4" pin or weaker with a 5.5" or longer pin position for less oil.

The Ultra Sonic did handle light to medium-light oil in general. It is a full pearl, if I recall correctly. Personally, I think the Mars core is slightly more easy to manipulate than the Sonic core, or it might be that the Mars-type covers & cores were better matchups than the Sonic's for me.
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"None are so blind as those who will not see."

Fast is going to be very similar to a Nomad Pearl
Fast having a strong backend snap if both are drilled the same way

look into a Mars with a 5-5.5" pin placement, pin up above the fingers

or a Neptune if you want a little bit weaker than the Mars
Mars is a great ball, and the hit and carry you get with it is amazing,

Ultra Sonic=The Boss

Anything with Sonic at the end= GOLD!

A Fast would look pretty good as a longer compliment to a Nomad for most IMO. Obviously more 411 would be useful, but as a generality.