I have read a couple different times about how greatest accuracy comes out of a 21 3/4" barrel. Seems to me that is a bit short for the higher capacity cases such as magnums. I was wondering if there is a rule concerning case capacity and optimal barrel length in order to burn all the powder in the barrel. I realize that the larger caliber will burn more powder in the same length barrel than a smaller bore and that burn rates will have a factor. Are there any studies on this? Ex: If a barrel that is "X" inches long efficiently burns all the powder in a 308 Win, then how much more than "X" is needed for a 30-06? Sorry if this is a stupid question and totally irrevelent and many thanks to any replies! -Wesseler.

Hello W

An astute question, and one for which I do not have the right math handy. Suffice it to say that the proportion of case capacity to barrel volume is something for which the barrel length can be optimized for velocity. Accuracy is another matter and the optimum barrel length is not likely to be the same.

Tom

Barrel length has almost nothing to do with how much of the powder charge burns. The relationship between the two seems logical but just doesn't bear up.

If anyone here cares enough for me to take the time and trouble, I'll compile some examples showing data for two things, which I'll explain here first. I must add, BTW, that what I'm about to say isn't personal theory or wild guesswork � it's sound interior-ballistics lore that sadly hasn't trickled down to us through "laymen's" firearms literature.

All the powder that's going to burn has already burnt by the time the bullet reaches a certain point in the bore, called "all burnt." Usually, there's still a bit more barrel left between "all burnt" and the muzzle. If some of the powder charge has NOT burnt by this point, it isn't going to burn at all.

Burning all the powder isn't what the "extra" barrel length is good for. Burning converts solid powder into a very hot gas under rapidly increasing pressure, and the gas expands rapidly. It's still expanding when the base of the bullet leaves the muzzle. Muzzle pressure varies somewhat, but it's substantial. Giving the expanding gas confined room to accelerate the bullet is the purpose of the barrel forward of "all burnt."

Experiments have shown, or so I've heard, that a centerfire barrel long enough to let the gas expand to its full potential volume has to be quite a few YARDS long. At least one experimenter I've heard of checked this out by joining barrels end-to-end until velocities starting dropping off.

If asked, I'll compile a list of several loads, with the figures for how much of the total charge burns, how far down the barrel it stops burning ("all burnt"), and the pressures at the maximum (peak) and at the muzzle.

Heck, I may do it anyway. I've seen piles of these figures but just noted them and went on with what I was more interested in. Maybe they'll be useful or interesting to somebody else one of these days.

The 21 3/4 inch figure for a barrel came from experiments by some guys shooting in a warehouse in Texas some time back and was in their opinion the optimum length for a barrel in 6mm PPC. This of course was regarding accuracy. Whether this barrel length gave the ideal pressure at the muzzle with the approx 27 gr powder charges they were using or what I really can't say. My opinion is that the 21 3/4 inch business amounts to folklore rather than solid science. It stands to reason that a change in bullet weight, powder charge, powder type, primer type or make, would change the entire equation. I always liked odd numbered barrel lengths because I had some real good ones but freely admit that this is superstition not science. Regards, Bill.

OK, and just to complicate things . . .

The longer barrel will "whip" more than a short stiff one. Barrel whip affects accuracy. Good accuracy depends upon getting the whip of the barrel to be in the same position every time the bullet leaves the muzzle.

Change bullets, load, velocity, or even case capacity and the whip harmonic changes.

But then, that's why people can get graduate degrees in ballistics.

Ken, I'd like to see some data if it's not too much of a problem. I had a link to some internal ballistic data from US Army Artillery school. Let me see if I can find it.

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PowderBurns Black Powder / Muzzle Loading Forum:

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Ken, please post your data here. Your E-mail symbol does not work for me. Thanks! -Wesseler

Simply put the 21 3/4" perfect barrel length is regarding harmonics and benchrest shooting. That theory came from Virgil at the warehouse shooting sessions. The longer barrels are for higher velocities. Short barreled hunting rifles are fast handling short range shooters. long barreled hunting rifles are for longer range
shooting. The ideal compromise is the 24" barrel. That is why most hunting rifles come with 24"barrels.
Benchrest rifles are designed to shoot one hole groups at 100 yards. Hunting rifles are designed to shoot a variety of ammo well for hunting purposes. Any hunting rifle that will post 1" 100 yard groups will harvest any game animal on the planet at ranges out to 400 yards with ease.

I learn more every day here. Can any of you estimate the optimum barrel length (accuracy, not necissarily velocity) for a .300 win mag built for 1000 yd shooting. Would this length vary depending on range of the target? 27" is what I planned on. Thanks for any info.

Wild Bill,

Under normal conditions (wind) at long ranges, velocity reduces error caused by wind variations (or errors reading the wind), to such an extent that longer barrels yield better hits at 1000 yards even though they might not do as well at 100 yards in a windless tunnel. For that reason you will see 1000 yard rifles with barrels out to 32 inches or so.

If you shoot from the NRA prone position barrel weight can extract a toll by the end of a string. I would say 26-28 inches is a good 1000 yard barrel length. If you can/could flute it without destroying it's accuracy, you might go 30-32 inches. If you shoot from bags/bench/bipod, the weightdoes not matter much. Lilja, Krieger, and K&P are famous for these long-range barrels. Pac-Nor now lists them as well.

Don

I was following a thread about the optimum barrel length for a benchrest rifle on benchrest.com some time ago. The explaination I saw from some of the top BR shooters (most shoot the 6mm PPC) was that length was not very critical to accuracy. The reason most used the 21 3/4 inch barrel was because with the maximum diameter (max stiffness) barrel allowed by the rules, chopping the barrel off at that length or close to it, allowed them to meet the 10 1/2 lbs. weight restriction for the Light Varmint class.

David,

Tha was my understanding also. 21.5" is optimal for a very specific set of requirements.

Don

Take a look at http://www.riflebarrels.com/ Dan Lilja has a few articles under the 'Fifty caliber subjests' about length, velocity, rigidity, ect.
To sum it up;
1) A longer barrel gives greater velocity
2) A shorter barrel gives less velocity

However,

3) A shorter barrel is less 'whippy'
4) A longer barrel is more 'whippy'

Sooo...
You need to find the longest barrel that allows the greatest rigidity for the best accuracy. Hence the 2" or more tube on a bench gun (long & rigid).

It's a good read just for the background info alone.

I received the following via email from William Tompkins. I checked out the link included at the bottom. I have never seen any of their barrels, or talked to anyone that has -- but what he says makes sense to me as a shooter and as an engineer. Their stuff looks impressive.

QUOTE: Great barrels can remain great even if fluted. It takes cut rifling not button rifling. We take a blank and drill it. Then we taper it if called for or just clean up the exterior. It then gets fluted, and put back in the machine for reaming. All the reamers get pulled through to get the bore to size. It is then transferred to the cut rifling machine where the grooves are cut in. Using this method, which takes no more than usual except for adding the fluting, you get an accurate barrel without the distortion imparted by fluting after a button is pushed or pulled through a bore.
Try air gauging a button barrel after fluting without the required lapping, watch the bubble bounce or even better just try to push a patch through. Lapping is absolutely required.
Currently I have 11 of these barrels shooting on a variety of firearms from field to full bench guns. All shoot better than I can shoot them which might indicate that I need help shooting! Anyway go to www. cutrifle.com and look at Dan Pedersen's work on barrels.
Shoot what you aim at and make it a small group.
Bill

cutrifle

See for yourselves. Anybody got one of these? Their Magnum action makes me drool.

Don

Once again we deal with an in-exact-science, based on a lot of theory by gun-nuts, with little proof of anything...now we have left out barrel harmonics!! oh well!

I THINK:
1. Short barrels are more accurate.
2. Long barrels get higher velocitys
3. Long barrels shoot better offhand.
4. Much of what we are lead to believe is
based on sales hype and gunwriters
trying despertly to hang in there and
make a living writing about something
that hasn't been written before..Lord
help'em...
5. I will exclude our own Ken Howell from
this accuzation, he's writes some good
stuff, along with his co-hart, Ken
Waters...
6. I repeat, this is what I THINK, I don't
claim it to be the last word in gunology.

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Ray Atkinson

ray@atkinsonhunting.com
atkinsonhunting.com