Answer the following Q with stream of consciousness. Context: As the slide of the pistol enters battery, the striker engages the sear. At this point, the sear is held back in a partially cocked condition. When the trigger of the M&P is pulled, the trigger bar first engages the firing pin safety plunger, lifting it upward, and releasing firing pin safety. At the rearward extreme of the trigger bar's travel, it engages the sear. The sear is rotated downward by the trigger bar, fully cocking, then releasing the striker. The striker makes contact with the primer of the chambered round, which in turn ignites the gunpowder and propels the bullet forward. According to renowned M&P gunsmith Dan Burwell, the angle on the rear face of the sear creates a camming action against the striker. This camming action moves the striker to the rear very slightly during the trigger pull, thus finishing the "cocking". This system is similar to the partially tensioned striker found in the Glock series of pistols. When the pistol cycles for the next shot, the striker will be automatically pre-set in a 98 % cocked position. Because the striker is only 98 % cocked prior to the trigger being pulled, Smith & Wesson classifies the M&P's action as "striker fired (double action only)".

Question: m & p shield 9mm single action or double?
To answer the question, consider the following: Because the striker is only 98 % cocked prior to the trigger being pulled, Smith & Wesson classifies the M&P's action as "striker fired (double action only)". Therefore, the final answer is double.