If I remember correctly, the O-ring stays true to the original mil-spec but Colt themselves changed to the spring setup because it tended to work better for various ammo. If I'm wrong someone will correct me, but thats my understanding of it. I have a DD with 3k rounds +(not all that much) and my backup BCG is a Spikes which has the springco spring setup but I've never had to use it thus far.

