Longer barrels

[David R. Pennington]

I was wondering if there is a relation to barrel length and breech pressures in long guns? Anyone discussed that before? Do longer barrels typically need higher or lower charges? So far I've only shot 42-44" barrels but have a 48" barrel .45 waiting on my next project.

[Paul Griffith]

I'm of the opinion that the same charge in a 48" barrel will produce slightly faster velocities than in a 42" barrel.  Dagner has a program dealing with such things & may chime in.

Paul

[Acer Saccharum]

With a longer barrel do you have issues of the ball residing in the barrel longer? Like if I were to flinch, would I tend to throw the ball worse with a long barrel than a short one?

But I don't flinch, really. 

[JTR]

Yes, a longer duration of the ball in the barrel, but, at 1800 FPS, it takes a ball about .023 of a second to travel down the length and out of a 42" long barrel. And with a 48" long barrel, it takes about .026 of a second to exit the barrel,,,, so about .003 of a second difference.

I say 'about' because I'm using a constant velocity, and not factoring in powder ignition, ball acceleration, etc.  But none the less, to make a difference in ball impact between the two barrel lengths, you're gonna need to be quick! 

John

[flehto]

I would think that the BREECH pressure would be the same irregardless of normal  rifle bbl length. After ignition, there's a "spike pressure" caused by projectile inertia and then a steady decrease in pressure as the projectile proceeds down the bbl.

There's a bbl length that allows  complete ignition to occur producing maximum velocity, but that length is load specific......Fred

[Acer Saccharum]

In other words, if the load is too light, the pressure will stop increasing while the ball is in the barrel?

[eddillon]

Longer barrels will result in higher velocities than shorter ones Barrel length has no effect on breech pressure unless the barrel is so short that the bullet exits before peak pressure can be attained.  In this case, you will blow a lot of unburned powder out of the muzzle.
Here is a graph from a software program I sell.  It depicts the pressure velocity curves as the bullet moves down the barrel from left to right.
 

RED line is the pressure curve.  Blue line is the velocity curve.

[flehto]

The above velocity and pressure curves would also be applicable to BP but the pressure would be considerably lower. The pressure "spike" overcoming projectile inertia is well illustrated along w/ the increasing velocity and  decreasing pressure curves as the projectile proceeds down the bbl. .....Fred

[David R. Pennington]

Very interesting. So in theory, I could expect to get a little more velocity which could result in a little straighter trajectory with no real change in breech pressure?
I remember reading somewhere (can't remember where) the reason the border scouts and pioneers liked a longer barrel was that it was quieter, or to say the report of the gun didn't carry as far a distance as the sound of a shorter barrel. This would be important if you didn't want to attract an enemy's attention or disturb the game in an area?

[Don Stith]

I don't have any black powder data to confirm or dispute the longer is faster claim. However, there have been extensive studies of the lowly 22 long rifle cartridge.  Maximum velocity is achieved at approximately 16 inches from the breech.  The friction factor reduces the velocity beyond 16 inches.
 I suspect a modest charge of black powder would behave in a similar fashion.
 The studies done with rimfire actually chronographed shots fired as the barrel was shortened incrementally. Any body got a barrel they want to sacrifice to reproduce the tests in black powder?

[LRB]

 It would depend on the powder load. Once maximum burn of the given powder load is achieved, pressure will decrease and the velocity would slow if the ball is still in the barrel at that time, due to lack of more pressure and friction. Think 5 gr vs 100 in a .54. The ball may not even leave the bore with 5gr. The pressure will wain at a given point, if the charge burns out before the ball has exited. Another way to look at it is from a fire hose angle. A 2 1/2" fire hose loses 10 lbs of pressure in every 50' due to friction loss. To get 100 lbs of pressure at the nozzle in 150' of hose, the pump has to produce 130 lbs at the outlet.
   Don, you entered as I typed. A very good example. With an equal load in two barrels of different lengths, the longer barrel will produce less velocity.

[JDK]

This has been done Don, and I've read it.....just can't remember right now.

Was it the back of the one of the old Dixie catalogs???.....I'll dig around, if somebody doesn't beat me to it.

Enjoy, J.D.

[Dphariss]

Trying to compare a 22 RF to a BP load is a mistake. Most 22 RF ammo is loaded with a pretty fast smokeless and the pressure drops rapidly past probably 12-14". With standard velocity loads a 26" barrel has a very low report due to sub-sonic MV and the pressure dropping very low at the muzzle.
Black powder is a different propellant.
It has characteristics of a fast smokeless and characteristics of a slow rifle type smokeless, from pressure data I have seen for BPCR. It will impart very rapid acceleration to a bullet but will continue to push it along in longer barrels.
But round balls are not bullets. I suspect that for MOST applications with Modern BP that barrels over 34-36" are of little benefit. But remember the Kentucky rifle prior to probably 1800-1810 did not have access to a modern BP. Powders such as Swiss, Schuetzen and Goex did not exist or at best were very rare in 1800. Swiss for example is much like the highly refined powders of the late 19th C. The technology was not really in place to even make this powder in the 18th C.
So when we look at the long barrels we have to look at them in the context of the powders that were available.
The shorter barreled guns with heavier barrel contours of the last 2/3s of the 19th C are, in my opinion, a rusult of the improvements in powder making starting in the late 18th and early 19th C.
If someone wants to test this they need to order a 48 or 50" rifled barrel blank, straight round is best, screw it on a Pete Allen action and start shooting it with a charge that produces a velocity in 1750-1800 fps range with each of various brands and granulations of powders. Then start cutting it back in increments. But this is going to take a lot of powder an lead if testing say Swiss, one of the other European powders, Goex and their premium powder and one of the cheap import "battle" powders is the barrel is cut back to perhaps 10-12" in 1" or 2" increments with a full range of testing at each length. No need to worry about a stock with the Allen action. The round barrel can be clamped in a set of v blocks. But a good quality chrono needs to be used and it needs to be 15 feet out to reduce damage from patches striking it.
If someone has the energy they could dig out a first edition of Lymans BP book and compare the velocity vs charge vs barrel length between the C&H they used and the GOI. The C&H, being closer to blasting powder than Swiss for example, was pretty poor stuff and took a LOT of powder to make much velocity.

Dan

[Pete G.]

Bullets are not propelled by burning powder; they are propelled by expanding gasses which are the result of the burning powder. I think the example cited about the .22LR was with standard velocity ammo. Since the .22LR has very little powder the pressure curve falls of pretty rapidly, but any load with more than a pinch of powder would take a much longer barrel (probably measured in feet, not inches) to see the same result.

Periodically some gunwriter will take a rifle, a hacksaw and a chronograph and prove that shorter barrels produce less velocity with normal loads, and just as often another writer will test ammo in two identical guns and have the shorter barrel produce a higher velocity. What is really proven is that there is no such thing as identical barrels.

The table in the Dixie catalog pretty much shows that longer barells and/or more powder = higher velocity. There are a couple of spots in the table that the data are so close as to be statistically insignificant, however I don't know if it really matters anyway.  You are going to build the rifle and work up a load that shoots well, regardless of the pressure or velocity.  The increased sight radius of a longer barrel more than offsets any ballistic concerns.

Sometimes I think we know too much and let it get in the way of things that really are important, like hitting where we aim. Natty Bumpo didn't know any of this stuff, and he can outshoot all of us; any day, any time.

[flehto]

If all the powder has been totally consumed in whatever length of bbl achieved this condition, then each addt'l  inch of  of bbl  length would provide only  friction which would decrease velocity. Once the pressure decreases, there's no addt'l force exerted on the projectile and then bbl friction would decrease velocity.....Fred

 

[doulos]

I don't have any black powder data to confirm or dispute the longer is faster claim. However, there have been extensive studies of the lowly 22 long rifle cartridge.  Maximum velocity is achieved at approximately 16 inches from the breech.  The friction factor reduces the velocity beyond 16 inches.
 I suspect a modest charge of black powder would behave in a similar fashion.
 The studies done with rimfire actually chronographed shots fired as the barrel was shortened incrementally. Any body got a barrel they want to sacrifice to reproduce the tests in black powder?

The boys at Rice Barrels sacrificed a barrel testing velocities.
heres the link
http://www.ricebarrels.com/velocity%20test.html

[Steve-In]

I see no benefit in comparing Black powder to smokeless.  They are truly apples and oranges.  It is my understanding that the internal ballistics of the two are completely different.

[Paul Griffith]

As far as truely long barrels, I've made or owned 5 barrels that were in exess of 60".  Two were 45 cal & 3 were 50 cal.  Making them shoot accurately didn't seem to be all that different as far as load, from say a barrel of 48"  The 50s used around a 100 grs of 2F which is about what we're running in the rest of the 50s.  I planed an 83"er  one time but never got to shoot it. My gut feeling is that flex should have been an issue. If a barrel could have been long enough for the pressure to decrease & actually loose velocity this one was a good candidate.

Paul

[rich pierce]

Don't encourage him.   . My limited understanding is that all this is also dependent on barrel bore diameter.  Even if one could make the same weight ball in 36 and .62, there's sure curves would be different in the same length barrel because of the volume into which the gasses can expand before the ball exits the muzzle.

[eddillon]

Here is a comparison.  The only difference is barrel length.  100 gr GOEX FFG.  .54 lead round ball. Barrel lenth #1 24".  barrel length #2 36".  Note velocity difference.
 



There is a limit to lengthening the barrel.  There is a point where the friction and the pressure that moved the bullet are equal to the air pressure in front of the bullet.  At that point the bullet comes to a halt.

[Acer Saccharum]

There is a limit to lengthening the barrel.  There is a point where the friction and the pressure that moved the bullet are equal to the air pressure in front of the bullet.  At that point the bullet comes to a halt.

Golly, there are comedians everywhere.

But you bring up a good point, Ed. Of course you'd not make a barrel as long as you jokingly suggest. Suppose you want to get maximum velocity for your powder. But you also want a barrel that is a practical length to load/clean and carry.

In the chart below, which I understand is for smokeless, I'd say there isn't a lot of gain past 10 or 15 inches. But what is the 'Point of little gain' for a muzzleloading barrel? And it seems like that point would be load-specific.

 

[JTR]

Can you stretch the barrel lengths out on your estimator?
The original question was the difference in velocity between barrels 42-44" and one 48" long.

With a 24" and a 30" barrel, of course you'll have an increase in velocity. The Rice barrel test showed that velocity was faster at 42", than in a barrel shorter than that. Question is, is it still increasing at around 48" barrel length, or has pressure peaked and friction has started to slow it down?

John

[Acer Saccharum]

John, it's my understanding that you can keep increasing the pressure, as long as you have the fuel to burn.

So if you have a longer barrel, yes you can get the ball to travel faster from a 48" than from a 32", as long as you have more powder.




But there are practical limits to what your shoulder can take, and are your arms long enough to load the rifle.

[doulos]

Can you stretch the barrel lengths out on your estimator?
The original question was the difference in velocity between barrels 42-44" and one 48" long.

With a 24" and a 30" barrel, of course you'll have an increase in velocity. The Rice barrel test showed that velocity was faster at 42", than in a barrel shorter than that. Question is, is it still increasing at around 48" barrel length, or has pressure peaked and friction has started to slow it down?

John

one thing interesting in the test conducted by Rice was that there was a decrease in velocity every time the barrel was shortened EXCEPT the 34 inch velocities were faster than the 36 inch velocity.

[bob in the woods]

Seems to me , there was a chart in a Dixie Gun Works catalog some while back that shows the velocity for a given charge in a .40 cal barrel that they cut shorter in increments.  Interesting. The velocity did diminish as the barrel became shorter, however the differences /variances increased as the length decreased.  That is, there was more of a difference between 20 and 30 in barrel, than 30 and 40 in.     If I recall correctly, the difference between 20 in or so and 40 or 42 in  was in excess of 200 fps