Barrel length measurements.

[7mm Eclipse]

How do you measure the effective barrel length for internal ballistics programs for a barrel with a muzzlebrake?

Is it the length of the barrel to the crown or to the end of the muzzlebrake or some point in between?

 

[barnesuser28]

When someone says their gun has a 30" barrel they are measuring from the crown to the face of the bolt, not the actual effective length of the barrel. when a muzzle brake is present you still measure from the bolt face to the crown.

Does this make sence?

 

[LouBoyd]

How do you measure the effective barrel length for internal ballistics programs for a barrel with a muzzlebrake?

Is it the length of the barrel to the crown or to the end of the muzzlebrake or some point in between?

For internal ballistics programs like Quickload barrel length is measured from the boltface (with the bolt in the closed position) to the end of the barrel rifling. That's whatever point the bullet travel "uncorks" the bore. For most bolt action and semi-auto rifles that's close to the same as the physical barrel length. If the barrel is ported (magnaport or similar) so that the barrel pressure drops as the bullet passes the port that point should be considered the end for the barrel for velocity and pressure calculations. The gas port on semi-auto rifles does have a small effect on muzzle velocity but it's ignored by most ballistics programs as are muzzle devices like brakes and flash suppressors.

The above is used for revolver type firearms too even though the input barrel length willl be longer than the "nominal" barrel length which by convention does not include the cylinder.

For ATF legal purposes the barrel length also includes any >permanently< attached muzzle device like a brake flash suppressor, or bloop tube. Porting is not considered, it's physical length only.

Also exterior ballistics programs (all I've seen) consider the starting point for ballistics calculations to be at the rifle's crown where the bullet is no longer supported by the barrel.

 

[7mm Eclipse]

Thanks to both of you for the information. It is appreciated.

Great explainations.

Mike