Brian,
What are you trying to achieve? If you are going to apply covering I suggest you apply with the nitrate then you can just brush on the Butyrate. If you are at the final coats then spray for a smooth finish. Ig you want to use an inexpensive spray system look in Home Depot for the Preval Spray System, come with 4oz jar. Make sure you strain the dope before spraying thin 60/40 ish thinner/dope.
Best, DennisT