How many spins the projectile makes over a measured length of distance. E.g., a 1 in 7 twist means the projectile makes a 360 degree spin in seven inches of travel.
The Springfield 1903 has a 1" in 10" twist rate. The later M1 service rifle also has a 1" in 10" twist rate.
You need to see a gunsmith.
1:16
It will vary with caliber.
The "rate of twist on rifling" is caliber specific. To give you an answer we would need to know which cartridge the rifle is chambered for.
Blue book of gun values
1/10
1/10
ar-15
Depends on caliber. www.countrygunsmith.net
The Remington Model 66 is chambered for the .22 long rifle cartridge. The most common twist rate for the .22 long rifle is one full turn in sixteen inches (1:16).
What is sightin-in a rifle mean?