Is there a rule for V gain / "of barrel

[Greenjoytj]

I would like to know if there is a general rule that describes the amount of velocity you would gain if a rifle barrel lenght was increased inch by inch?

 

[rafterob]

For a given amount of powder in a barrel of length to efficiently burn it, my guess is added length would reduce velocity due to increased friction.

 

[Stumpkiller]

It's an "S" curve. There will be a length that optimizes any given powder charge but then it plateaus and heads down. Also depends where you start. If you go from 12" to 13" you get a better return than 30" to 31" (Law of Diminishing Returns).

No rule I am aware of, though I'm sure someone has made something up to cover it. I know there is such a thing to tell you the optimal length of a barrel as far as burning efficiency - but that is independant of accuracy or effectiveness. It may well be worth burning 30% more powder to get 20% more energy if you're actually hunting with the weapon instead of just exercising your mind.

 

[zimmerstutzen]

In this day of different granulations, qualities of powders,and fake powders, as well as twists and chokes, I'm not sure there is a general rule like you request.

There is a point in lower charges that the velocity seems down due to being mostly consumed prior to the ball exiting the muzzle. With moderate charges longer barrel lengths generally lead to higher velocities. With heavy charges, it would seem to vary depending on bore diameter and length.

There are so many variables, that I don't think it probable to come up with a formula that comes reasonably close. Back in the day, when Goex was about the only powder available throughout much of the country, perhaps. Between Swiss and Kick there is a big difference in velocity just in the same barrel length.

 

[Herb]

Go to www.ricebarrels.com. On the left, click on NEWS and then TEST. They chronographed a .50 caliber barrel 44" long with 80 grains of Goex 2F and a round ball, four shots, then cut it off 2" and chronographed again, down to 30". The velocity change is not linear, but that is real life. I have chronographed many thousands of rounds through ML rifles, .36 to .58, and sometimes there are what look like inconsistencies in the velocities with changes.

 

[CoyoteJoe]

I agree Herb, I've seen lots of variations myself. Speaking of blackpowder and round balls only:
As you work up through progressively heavier powder charges you do not get a smooth progression in velocity. Many people will start working up in increments of 5 or 10 grains, hit an increment where they see little or no increase in velocity and say "aha, that is all the powder she will burn". But not so, if they had continued on to the next increment they may have seen a large leap in velocity.
The only way you'll see a smooth progression is the way it was done in the Lyman books. Plot all the raw data on a graph, then draw a smooth curve to come close to most of the points but not necessarily hit all of them.
It may be possible to load more powder than a barrel will burn but it will be more powder than any sensible person would actually try to shoot.
It may be possible to make a barrel so long that the ball actually slows from friction but it will be a longer barrel than anyone would want to carry.

 

[Larry Pletcher]

Go to www.ricebarrels.com. On the left, click on NEWS and then TEST. They chronographed a .50 caliber barrel 44" long with 80 grains of Goex 2F and a round ball, four shots, then cut it off 2" and chronographed again, down to 30". The velocity change is not linear, but that is real life. I have chronographed many thousands of rounds through ML rifles, .36 to .58, and sometimes there are what look like inconsistencies in the velocities with changes.

Dixie's old catalogs has charts at the back. One covered a test done as the Rice test above. I don't know if it is in the more recent catalogs.
Regards,
Pletch

 

[hawkeye2]

The results of a test were published in the "American Rifleman" many years back (early 80s?). in which they cut a revolver barrel off 1" at a time and chronographed the results. I'm sure the catridges were loaded with smokeless and the results were very interesting though they might not equate to blackpowder. The revolver was a Colt single action and I believe it was a .45. I think they started with a 12" barrel and the last two tests were with the barrel cut off flush with the frame and with the barrel completely removed. The drop in velocity was much less per inch that I had imagined it would be. By the time they had cut the barrel flush with the frame the muzzle blast and flash were pretty impressive and it was found that with the barrel stub removed the threaded frame acted as a fairly efective flash supressor.

 

[Rifleman1776]

Many people will start working up in increments of 5 or 10 grains, hit an increment where they see little or no increase in velocity and say "aha, that is all the powder she will burn". But not so, if they had continued on to the next increment they may have seen a large leap in velocity.

Amen, brother. Those inconsistencies and confusions are what make this crazy avocation so much fun and keeps the jug going around the fire. If it was all cut and dried we would find something else to do.

 

[hanshi]

There are several but they all fall apart in the cold light of day and in real, everyday barrels. In my .40, going from 35grns to 40grns (just 5 grains) increased velocity by nearly 300fps. The next 10 grains much less than that.