"Coil lock" could mean two different things: 1) The coils of a pilot chute spring get caught on each other, or; 2) The pilot chute fabric is tucked under the base of the pilot chute, thereby locking the pilot chute in the compressed position by it's own tension. For #1, this used to happen, rarely, when pilot chute springs were made with the same diameter throughout their entire length. A coil could interweave itself amongst another coil, thereby locking the coils together, effectively reducing it's length and effectiveness. Newer pilot chutes now have tapered springs, that are smaller diameter on the base, and larger diameter at the top. Thus it's more difficult for the coils to get caught on each other. For #2, the practice used to be to stuff all the loose fabric under the base, but that meant that the pilot chute spring expansion was restricted because it was being held down by it's own skirt. The idea was that it helped serve as a good base "kicker plate" for launch, and also prevented a loose spring end from burrowing down into the canopy fabric and getting itself stuck there. I think the practice now is to stuff the loose fabric around the coils a little at a time along its entire length, so that it doesn't restrict expansion, or else lay the fabric outside the coils.
