General discussion > Gun Building
Question on barrel length and harmonics
Artificer:
I hope Daryl will understand I have to use some modern gun experience and references to ask this question about muzzle loading barrels.
From over three decades of working on or building M40A1 sniper rifles, NM M1 and M14 rifles and other competition rifles, I'm a true believer in getting the harmonics and length of barrel correct for the caliber, load and/or bullet used.
We defined harmonics as the vibration of the barrel as the bullet is traveling down the bore. The vibration acts like waves. We have found that a barrel is most accurate when the bullet exits the bore when the wave is at the bottom of it's curving up and down movement. That either means you have to cut the barrel to the length of where the wave is at the bottom or change the load and bullet. I admit I'm not absolutely certain this applies equally to muzzleloading barrels as much, but basic physical laws don't change whether it's a modern or muzzleloading barrel.
We get into something along with that and it's known as negative nodes of vibration will hurt accuracy due to the interuption of the vibrational waves. A negative node of vibration is set up on a muzzleloading barrel by the pins or keys used to attach it to the stock. I don't know for sure, but I'm pretty certain that most ML barrels aren't affected too much by the negative nodes of vibrations of most pins and many keys. I also know that sometimes the key used to almost imperceptably bend barrels will sometimes make them shoot better if there is not too much stress on the barrel.
So what I'm asking is has there ever been testing done with a muzzleloading barrel to see what length is best for harmonics for the patched round ball in a certain caliber?
I realize there are some real problems associated with that for the barrels we commonly use on American Long Rifles and other 18th century rifles and that's part of the reason I'm asking. You can't just cut off an inch of barrel at a time to shoot and test a swamped barrel as the change of the outside dimensions will most likely cause more differences with harmonics than just cutting off a barrel that has pretty much the same outside dimensions all the way down the barrel.
I also realize that changing ball size, patch size and powder type and volume will make huge differences in the harmonics of a barrel, as well. I can't tell you how many times over the years I've used the examples of muzzleloading to explain these things to modern gun shooters who have never gone through a lot of testing to find the best bullet, patch and powder load for a rifle. ML shooters have a distinct practical advantage in this regard as it's far easier for someone with a ML background to understand why a 168 grain match bullet works better in his Garand than a 173 grain match bullet does.
So to tie this up for a muzzleloading barrel question, what I'm looking for is there such a thing as the best length and shape of barrel (along with the rifling twist of course) that makes the barrel more inherently accurate for round balls in each caliber? IOW, does a 42" barrel (or whatever length and shape may be "best') in .45 caliber have an advantage over a 34", 36", 40", 42" or 44" barrel for barrel harmonics?
Thanks in advance, Gus
T*O*F:
--- Quote ---We defined harmonics as the vibration of the barrel as the bullet is traveling down the bore. The vibration acts like waves. We have found that a barrel is most accurate when the bullet exits the bore when the wave is at the bottom of it's curving up and down movement. That either means you have to cut the barrel to the length of where the wave is at the bottom or change the load and bullet.
--- End quote ---
This was discussed on the old MLML, long before the "message board" format even existed.....maybe around 1996. We had a number of engineers of various disciplines who worked this out mathematically, for a straight barrel. The result was that a 42" barrel was the "ideal length" for a muzzleloader.
I don't remember much else about the discussion except that we thought it to be extremely coincidental that this was the average length used by the "old timers."
I still have the archives of that list, except it is comprised of years of text based emails and almost impossible to search.
Artificer:
Thank you for the information. I wasn't around the original board until a few years after 1996, so I missed it.
No need dig through the archives. It makes sense that through trial and error the original gunsmiths found what length was best and used that the most often.
Just one more question, though. Does that also go for swamped barrels to a degree or is it confined to purely straight barrels?
JTR:
I certinly can't answer this question with any degree of expertese, but when I was shooting 22 rimfire rifles in competition we used adjustable barrel weights on the muzzle to try to tune the harmonics.
I wonder if the swamp on a ML barrel somehow acts the same?
John
Larry Pletcher:
With barrel tuning on the Browning Boss, the velocity was a considation. To exit the muzzle at a certain spot in the harmonic wave, I'd speculate that the velocity (time in the barrel) must be a part of the equation.
With muzzleloaders we are careful to produce uniform loads and small variations in velocity for a reason.
Regards,
Pletch
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