I am going to make a test here.

For Pattern-Coat™ Primer through the Gel coat cup gun, thin down using 25% acetone to get a good even spray characteristic.

For Pattern-Coat™ Hi-Gloss, when spraying, thin the Pattern-Coat™ Hi Gloss using pure acetone at a ratio of 25%.

1. Start by spraying a 'mist coat' over the pattern. Wait 2-5 minutes for the solvents to evaporate.
2. Pattern-Coat™ Hi-Gloss can be applied wet-on-wet but sufficient time must be left between passes (2-5 minutes) to allow time for the solvent to evaporate. Around 5 passes should leave a sufficient thickness of Hi-Gloss to ensure the surface can be properly flatted.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Further to Warren's advice, you do not need to dilute down the GC 50 with acetone as this can be sprayed un-diluted

For the Pattern Coat primer and High Gloss, I've found that using the FN4 nozzle, which is about 3mm I believe, gives a much improved spray pattern and finer finish.

I just buy the gelcoat gun from EC, there is only one nozzle, 4.7mm.

In the UK, East Coast Fibreglass sell other sized nozzles and I'm sure that there are also plenty of suppliers in the US if you search

The standard nozzle is fine for gelcoats such as GC50.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant