The detents only prevents double-feeds, won't prevent roll-outs since it's closed-bolt like autocockers (and most other pumps). So the barrel's bore holds the ball in place. The stock barrel has a "triad" system, which is simply an o-ring stretched over 3 open slots on the back of the barrel. Sides of the o-ring protrude into the barrel bore, acting as roll-out prevention. May want to use the stock barrel unless you can get paint that's .685 or larger, or get a smaller bore barrel.