I'd go hollowpoint as well if you really feel you need a bolt upgrade. The stock one isn't bad at all. I thought it was the same as an Ion bolt but then when I got my vibe I realized it's hollowed out of the front, so its about halfway between a stock ion bolt and a firebolt. Probably the last thing I would upgrade.
In order to see any major performance difference, the Blackheart kit is the way to go.
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I'm getting the NDS tech site going again. ndspb.proboards.com PM me if you would like to help make tech tutorials to help out the paintball community.