Barrel length vs. Tragectory

[OneMoreDeer]

Has anyone ever seen a comparison of barrel length and trajectory? Most reloading manuals list barrel length for a particular load that produces xxx fps. All of the ballistic programs that I have seen ask for the ballistic coefficient and fps to determine bullet tragectory. If a test was performed on two different barrel lengths(for example a 20" barrel and a 24" barrel), assuming identical bullets,twist rates, and muzzle velocities, would their flight paths be identical?? How about fps at regular intervals ie: 100,200,300 yards? I am trying to understand the relationship (if there is one) between barrel length and bullet stability. Does a longer barrel mean a flatter or more stable flight path?

[1st cav sgt ret]

Ok Ill give this a stab(GonHunting feel free to join in anytime)if the three varibles you list bullets,twist rate,and muzzle velocities are the same then trajectory will be the same,however with the longer barrel you will have to use less powder charge to achieve the same velocity,,,,in other words the shorter the barrel length the larger the powder charge must be to be able to match the velocity of a longer bbl.with all other things the same

[GonHuntin]

Interesting question! In your example, the 24" barrel would have 4 more inches of length to "work" on the bullet.........if we are dealing with a 1 in 7" twist, for example, the bullet would turn 4 complete revolutions in a 28" barrel and only 3 in a 21" barrel....don't know if that would cause the bullet to more stable in flight or not?

Since trajectory is a function of bullet velocity, weight and ballistic coefficient (which itself is a function of bullet velocity among other things!) I don't see how the extra barrel length (assuming identical velocity from both short and long barrels) would have any effect on trajectory? Unless, the extra barrel length would cause the bullet to "go to sleep" quicker?

As I understand it, and someone correct me if I'm wrong (Mohawk?), when a bullet "goes to sleep" it is rotating perfectly perpendicular to it's axis of length.....in other words, the bullet is not exhibiting any yaw.....if the longer barrel causes the bullet to sleep sooner, it may result in conservation of velocity as compared to one that goes to sleep later....which may result in a flatter trajectory......

I'm betting that you would have to test this in a laboratory to see any difference

Hopefully, Mohawk or one of the more experienced long range shooters will jump in and 'splain it to us! I know that staying supersonic out to the target is a big concern to ultra long ranger shooters.....the transition between supersonic and subsonic sometimes does strange things to bullet flight......

[OneMoreDeer]

Thanks for the reply Sarg. I understand the relationship between barrel length and fps. It has long been reported that an inch increase in barrel length will increase velocity by 50-to 100 fps, although I read an actual study that this is not always the case. The study showed that this is not a linear comparison, and increase of one inch does not always mean that you will gain xxxfps. If that were true, we would be shooting guns with 100 inch barrels at 10,000fps. What I am interested in is the downrange effect of a longer barrel( more time in the tube) on the bullet flight path with all other factors being equal.

[texasshooter]

OMD,

In my experience, each additional inch in barrel length adds closer to 25-50 fps. I don't think it's as high as 100fps and obviously there is a point of diminishing return. That being said, a lot of the 1000yd bench rest competitors are using barrels that are 30" in length. Since velocity has a lot to do with trajectory, then I guess you could say that barrel length does have some effect on trajectory.

[1st cav sgt ret]

Ok then onemoredeer as I dont know you and have no idea as to your level of experance,I can say that in cowboy shooting wherein(useing an extreme example) a 45/70 used in a 20in bbl(cast bullet and pyrodox)and a 30in bbl(same ammo and the ammo is chronoed at 1320 from the short bbl and 1560 from the long bbl)at 100yards the short bbl will shoot lower than the long bbl due to the effect of recoil(which is another variable)meaning more lag time in the bbl which will throw the shot higher,the longer bbl will maintain its accuracy at very much longer ranges due to increased velocity and increased sight radius(another variable),,,therefore the only way to test your theory would be to be tested in a laboratory wherein all possiblevariables can be controlled

[OneMoreDeer]

Texasshooter, I agree 25 to 50 fps is a more realistic figure per inch of barrel length. Different calibers, bullet shapes ect. all have an effect on the actual gain that would be seen. I also agree on the point of diminishing return. Those that shoot the 1000yd matches seem to lean toward longer barrels. If you look at long range shooting history, 30 to 34 inch barrels were common particulary with the black powder cartridges. Thanks for your input.

Sarge, I have been reloading for the last 35 years, starting with shotshells and progressing up to centerfire rifle and pistol. Starting out, it was just following the directions in the various reloading manuals. My interest grew from building ammo to hunt with to customizing the most accurate ammo for a particual rifle or handgun.
I am not a benchrest shooter, just a guy that enjoys getting the best accuracy possible out of a particular gun. I agree, the answer may be out of reach except for those who have a lab to control as many variables as possible. I am always looking for answers and thought maybe someone had run across some info that would answer this question. Thanks for your input. By the way, Gonhuntin is my brother.

Good Shooting

Doug

[GonHuntin]

Hey guys, I think you are missing the real question OMD is asking......notice his question assumes identical barrel twist rate, bullets and muzzle velocity.....but different lengths.

You may think this is an impossible situation, but it is not. There is a point, for any given cartridge, that added barrel length does not = increased velocity......even if that were not the case, the question still has merit because it assumes a specific set of conditions and asks what effect one variable (in this case barrel length) has on the outcome. I believe this example has real world application and that this question has been answered by shooters who compete at ultra long range.....I hope we can find the answer......

If you are having trouble understanding the "sleeping bullet" discussion and how it can change trajectory, think of it this way:

Let's say we have two identical cars launched by a big rubber band, down an ice covered road.......the rubber band launches each car at 35 mph......car number 1 travels down the road sliding and fishtailing, car number 2 travels down the road in a perfectly straight line......at 1/4 mile from the launch point.....which car is going faster?

I believe the same can be said of bullets.......Logic tells us that one that "goes to sleep" sooner conserves velocity and, in theory, is going faster at 800 yards than one that goes to sleep later......but I could be wrong? ;D

[Mohawk]

Gentlemen,
Normally I wouldn't even have the balls to offer my two cents here seein' as how I so unequivocally 'stepped on my own dick' with starting that thread on whether its 'safe' to put more of a given powder in a given cartridge case than a given manual recommends. But Mark said I should say somethin' (he flatters me and he knows it), so let me offer the following based on the experience I've had shooting various rifles to considerable distances.

First of all, we all realize that it stands to reason that two different rigs of exactly the same setup, right down to bore twist, chamber and bore runout (which is almost impossible), and even the batch of steel from which the barrels are hewn, will perform in largely different fashion based upon the sole variable of barrel length. And we accept that the rig with the longer barrel will do better at long rage by virtue of the fact that the mean MVs it yields with given load will be greater than those generated by the rig with the shorter barrel. But strangely enough, this is not always the case. Serendipitously, rifles (both factory and custom) do come along wherein flatter trajectories are realized withstanding shorter barrels. And rifles made for long range performance, having 26"-30" barrels, sometimes fall short of design projections.

Not only have riflesmiths who have built for me warned me of this phenomenon, but I have actually seen it happen. And no one knows exactly why it happens! They just chalk it up to that obscure reason widely known as 'barrel harmonics'. Whatever!!!

One thing that a couple of people who might be legitimately regarded as ballistics gurus have told me is that the phenomenon of 'yaw' has more to do than anything with whether a rifle -- regardless of barrel length and/or MV of the projectiles it fires -- will hold elevation at longer ranges. Now, I understand this phenomenon as being more or less a matter of the degree to which a projectile 'pitches' (in wholesale fashion) to the direction in which it spins, in as much as it also turns on its own axis. Illustratively speaking, note that a high velocity rifle projectile with an extreme amount of 'yaw' actually 'corkscrews' through the air. And this, regardless of how fast it comes out of the barrel through which it is fired, will slow it down faster than a bullet having an initial MV that is lower, but has less 'yaw'.

And that's about all I have to say about that!
Dave

[1st cav sgt ret]

hey Mohawk thankx for your input,as to steppin on somthing I think its more like stepping in something IMO we just need to be aware that some folks arent "advanced"reloaders and not everyone is benchrest shooters,,,however yourself and onemoredeer do ask and inquire on some difficult and interesting questions that really push the envelope and make or test ones thoughts ideas and abilites

[OneMoreDeer]

Gentlemen: I do appreciate all the input into this perplexing question. With all of the possible variables to contend with, and absolute answer may be impossible. IMHO a good starting place would be to use the same test barrel and shorten between tests. I do understand the concept that Dave mentioned, "barrel harmonics". When a barrel is shortened, it becomes stiffer and has less area to vibrate much the same as cutting off a tuning fork would change the tone. Load development to achieve exactly the same MV would present yet another hurdle to overcome.

My question was inspired by the influx of all the new "super" cartridges coming on the scene. The premise that shorter, fatter cartridges are more efficient, more MV with less powder. I wonder if the same idea could be used on barrel length(read- most efficient). I guess we are all looking for the most BANG for our buck......pun intended. The bottom line may be the intended use of the rifle or handgun in question. I look forward to future discussions and the opportunity to learn, that's why I joined this group. Again, thanks to all for their input.

Good Shooting in the New Year ;D

Doug

[Mohawk]

Doug,
Wow! Good questions, partner! But they're the stuff of ballistics engineers/researchers. Or if anyone here can answer them, my hat is off to them! As for me, I was out of it several chapters back!

To all you and yours, Merry Christmas . . . or should I say, may Christ Jesus bless you and keep you this night and always!

Dave

[littletoes]

Thanks Mohawk! The same to you and everyone else here!
I have read such a study done by Dan Lilja. I think it was a 42" barrel that he started with, moving down 2 inches at a time till he had gotten to 24". Very interesting stuff. His studies showed that not many cartriges could take advantage of the full 42" length that he started with. And also the "whip" that resulted from such a long barrel (even at 1 1/2" in diameter), resulted in extremely poor accuracy. He showed in his sutdies that most calibers did their best somewhere in the mid-thirties, and lost velocity steadily while working down in length.
As to the super magnums, if you pile enough powder on something, sure it will go faster. But at what eficiency? And cost? As to the accuracy, it should be attained to a shorter, stiffer action, and a shorter powder column. Powder burns inconsistently, so the shorter you make that powder column, the more you eliminate this. Inconsistency is the largest denominator or inaccurate ammunition. That is what we are trying to achieve. Eliminate the bur inside flash holes, uniform primer pockest, uniform necks, ect. ect. Inconsistencies. Eliminate them, and it will be easier to predict what said ammo will do/perform.
As to the Yaw of Repose, if you have a right handed twist barrel, your bullet will cut to the right. The farther it travels, the more it will cut. Correct?
But, are we venturing into what is called "The Magnus Effect"? Which is the downward force caused by the pressure difference between the top and bottom of a bullet in relation to the air molecules around it as it travels downrange-I think? Not much help, huh?
You guys make my head hurt! What happened to just plain good old fashioned shooting? Trial and error? LOL!