What is Barrel Length?

[Jakalas]

I have been wondering about this topic for some time and would appreciate your comment on this.
What is it that is considered barrel length? Is it the chamber including the throat plus the bullet bearing grooved surface?
In my opinion if I compare the COL of a .375 H&H to that of a .308 Win the difference in length is .800"
That will mean that if the length of a barrel is measured to include the chamber a 24" .308 Win will in actual fact have a +/-.800" longer surface for the bullet to travel in.
In other words, if the billet of a .375H&H measures 24" at least 3.3" (taking cognizance of the ogive) must be subtracted to work out what is the length of the grooves the bullet is travelling on.
It can therefor be argued that the old adagio pertaining to velocity in a longer or shorter barrel be calculated only in as far as the length of the grooved surface.
Am I correct in my thinking?

 

[ZG47]

No. The rule was established by artillery men, many years ago. Same for a small arm as for a 155mm gun or a 120mm tank gun. Barrel length is measured as breech face to muzzle. The physics of the combustion process are essentially the same, whether it occurs in a muzzle-loaded cannon, a muzzle-loading musket, rifle or pistol OR a breech loading firearm utilising safety ammunition.
N.B. If you were to only count the rifling length, you would really go wrong with a B.S.A. air rifle because they have several inches of so-called counter bore i.e., a smooth internal section of barrel between the end of the rifling and the muzzle.

 

[Desperatezulu]

Simple answer: (closed) bolt face to crown = barrel length.

 

[Luvthunt]

#1

 

[fourfive8]

@Desperatezulu is correct. Easy to measure. Run rod into bore until it contacts closed bolt face/breech block face. Mark at muzzle (crown). Measure

 

[Wyatt Smith]

@Desperatezulu is correct. Easy to measure. Run rod into bore until it contacts closed bolt face/breech block face. Mark at muzzle (crown). Measure

That’s how the ATF will measure if they think you have one that is too short.

 

[Jakalas]

Simple answer: (closed) bolt face to crown = barrel length.

This has always been my thinking as well and I believe is correct. But it does leave room for error when you look at things from a ballistic perspective in that the rifling on a 24" 375 H&H barrel would be shorter than the rifling of a 24" .308 Win barrel.
I however know that by definition the barrel definitely includes the chamber etc. and hence you are correct.
What got me thinking about this was the answers given by members as to velocity loss when shortening a barrel. I very much doubt their can be a fixed formula to determine a clear answer taking into account all the variables i.e. propellant, burning speed, pressure, chamber dimensions, seating depth, etc - all other things being equal, bullet, weight

 

[Desperatezulu]

But it does leave room for error when you look at things from a ballistic perspective in that the rifling on a 24" 375 H&H barrel would be shorter than the rifling of a 24" .308 Win barrel.

What error? Why is length of rifling on a 375 being shorter than a 308 significant?
Remember twist rate is more important for bullet stability than barrel length - a rifle with a tighter twist rate technically has a longer length of rifling than a slower twist rate, even if the barrels are the same overall length.

Velocity loss is calculable - just lots of variables to factor in as you mention. Doesn't mean it can't be done by a fixed formula. It's just not a simple one. As an example the powder variable - faster powders are sometimes suggested for shorter barrels to achieve similar velocities to a slower powder in a longer barrel. There are limits to what can be achieved obviously - in general a longer barrel lends itself to higher velocities.

 

[fourfive8]

Yep, I don't think all the minutia about barrel length or internals like neck, throat, leade, rifling details, twist, etc. matter much at all compared to what the chronograph says. When you see published pressure/ballistic data by major sources that list the test barrel length, they use the standard method of measurement as already described in this thread. The most I've seen marked barrel lengths vary versus actual measured lengths is about 1/4" where a barrel with a 24" marking may actually end up anywhere between 23 3/4" and 24". The labs who publish data certainly don't use some odd method like neck to muzzle or throat to muzzle or bullet tip to muzzle, etc. And if you are having a custom barrel put on an action you can specify any length you want if you think there may be some advantage to a barrel with a chamber neck to muzzle length of exactly 24" (or whatever you choose) vs one conventionally measured and marked 24" but with a neck to muzzle length of maybe 21-22".