Thread: 22lr barrel length

About bolt opening before bullet leaving barrel. A semi bolt travel back may START before a bullet has left the barrel, but nowhere near so far as to start venting gases to the rear.

In straight blowback the bolt travels back as an aqual opposite reaction (remember physics). So if a 1gram bullet exits at 1000fps then a 250gram bolt will travel back at 1/250th of the bullet speed, because that is the ratio of the two masses traveling apart. So 4fps bolt speed back vs bullet 1000fps ahead.

In reality you have to add the mass of the spring to the bolt mass.

Initial bolt travel speed is independent of the spring strength. But if you use an underweight bolt you need a strong spring to decelerate it.