I've been fortunate too have spent multiple winters on the North Shore working under the tutelage of sensi Jeff Bushman (arguable one of the best 'gun smiths' in the world), working with Bushy firsthand has given me a great insight into gun design and a fair bit of experience shaping them..
Due too the specific needs/requirements for guns i only make them as custom orders for individual riders, i have 3 main templates that i work form:
1. TubeShootah - this is your regular shortboard step up, usually ordered a couple inches longer than your shortboard as a step up or a few inches longer as a semi-gun, a little more rocker, a slightly more pulled in nose/tail and slightly tapered rails, its basically a shortboard template geared up for faster/better waves, usually i do these from 6'0 - 7'0
2. WarPig - this is your mini gun, usually ridden 12" or so longer than your regular board, a slight vee bottom, a narrower outline with wider nose and tail, a beak nose too keep forward volume and a bit of rocker, a board for cathing waves but still having enough sensitivity too utilize all the speed.
3. ChubLorde - this is my full gun, available from 8'0 - 11'2 - a serious board for serious waves,