I did some flipping through FM23-10 (US Rifle Caliber .30 M1903).
Para 43 starts bolt manipulation exercises. The trigger was tied to the rear to ensure that the bolt required the correct camming force to open and close. Then they cycled the bolt with the initial goal of 20 times in 20 seconds. A trained operator could get off an aimed shot every 4.5 seconds. Special emphasis was given to make sure the shooter did not take his eyes off the target at anytime.
They also did cadence exercises starting at 10 seconds per shot and working down to 6 seconds per shot.