What is referred to as "straight blast" these days is what martial artists commonly refer to when speaking of Mr. Lee's straight line hitting method.
To be more distinct, the leading straight right or "straight lead" with the strong hand positioned in the front of the stance is the cornerstone punch of JKD. This was the tool he refined the most out of all the punches or kicks. It generates the most force within a small distance and he practiced it constantly. Most of his training was done with the lead side. The training was not symmetrical.
My former instructor acquired Bruce Lee's bag training gloves from the first Bruce Lee estate auction in 1994. The gloves were originally black leather, but the right glove is worn to the point where the entire hitting surface has almost no black enamel on it and is conformed to the shape of Lee's fist. The left glove is also worn, but with only a couple of cracks.
The main mechanical difference between Lee's straight lead and chain punching is the utilization of the footwork mechanics to generate force behind the punch. The position of the hand is nearly exactly the same, with the fist landing vertically and the elbow covering the center line. When executing the straight lead, a forward pushing step is delivered with the back leg pushing against the floor with the heel raised. This transfers tremendous kinetic energy into the lead hand that is being thrust forward. The combination of the kinetic energy from the step and the whipping motion generated by the body turning and the hand extending in that fashion all contribute to how the movement is properly done. This enabled him to be able to hit not only very quickly, but with tremendous power and in combination. This was done in a different fashion than the WC version of "ching" internal force or by use of small circular steps.
"Attack by combination" was one of Lee's tactics, the five ways of attack. Different combinations were practiced, including those similar to the WC chain punch, but also some similar to boxing. Punching drills I went through included a lot of lead with push step/hook with circle step, lead with front shuffle step twice/rear cross with push step combinations. There were also hand/foot combinations such as lead front kick to shin with pendulum step/lead punch with small push step/lead hooking kick with burst step. Indeed, there are many attacks by combination. The boxing and WC type of tactics are only a few of them.
A lot of these mechanics are referred to by martial artists as "straight blast", but the intricacies of each movement are what make them work. To me this means the true cornerstone of JKD movement is in the integration of the fighting position with the footwork. The lead hand punch was simply Lee's main tool of conveying this.
"After all, we all have only two arms and two legs."
"Death is certain, life is not."