Point of Deminishing Return on Barrel Length...

[Shane Tuttle]

I've tried a brief search on optimal barrel length on a rifle generally speaking and it got me to thinking:

Understanding in general terms, longer barrels provide greater velocities and usually a more precise shot. But, where is the point of diminishing return? At what point does length become a detriment?

My parameters are quite loose. I'd like to take a look at, say, a target rifle set up for about 600yds+ using .308Win for commonly known cartridge. Also, take your standard accepted twist rate and bullet weight/ogive in context.

If you want to use other examples, by all means bring it on.

What I'm thinking:
1. If I use a widely accepted case, powder, primer, bullet combination etc., the friction of the rifling will start to play games with the force of the propellant.

2. Too much time in the barrel, although minute, will take a toll on the bullet.
3. Even if you have a pretty heavy barrel, harmonics have got to wreak havoc one way or another.

I'm a simple minded guy and have a hard time comprehending the complex formulas that entail the theories. If you need more details in order to provide a more specific explaination, let me know. I'm trying to keep it basic to get a grasp on the theories and then try to add the meat & potatoes. So, what say you?

 

[Jimro]

The point of diminishing returns depends on the cartridge. There was an interesting article I read a bit ago about how to use a standard 20 inch 22lr barrel to produce the effects of a silencer by having such a small charge that the bullet actually pulled against a vacuum just before it exits the muzzle.

A 308 Palma rifle can have a 28 inch barrel and the shooter will handload to get full use of that length. A commercial load in that same rifle won't get any real special benefit from the length. Palma shooters find the lightest brass they can and pack it as full of powder as they can.

An m24 Sniper rifle is also in 308, but it is optimized to shoot heavier bullets 168-175 grain match bullets. It has a 24 inch barrel.

In both cases the powder will have a complete burn within the bore (around 20 inches) of the rifle, at the end it is only the expanding gasses that give an added velocity bonus for the longer barrel.

Obviously this changes if you talk about a larger capacity cartridge such as a 300 WSM, the more powder the brass can hold means the more gas the powder can produce.

Now as far as barrel harmonics, a shorter barrel is stiffer than a longer barrel of the same diameter. So in order to have a stiff long barrel you have to increase the diameter. Long thin barrels can produce tight groups (think 91/30 PU sniper or SVD) but usually they need time to cool between groups.

Short stiff barrels are favored by a lot of the benchrest crowd, for good reason. It is one less thing to worry about. The reason why barrel harmonics are important to accuracy is that the muzzle vibrates, and the stiffer the barrel the smaller the deviation in terms of amplitude, which means smaller deviation in muzzle deflection.

To sum up, the more "overbore" a cartridge the longer the barrel can be in terms of increasing velocity. The shorter a barrel the stiffer it is.

Here is some more reading material.

http://www.riflebarrels.com/articles/bullets_ballastics/long_barrel_velocity.htm

Jimro

 

[Shane Tuttle]

Short stiff barrels are favored by a lot of the benchrest crowd, for good reason.

I wouldn't have thought of this, Jimro. I was guessing that you'd want the longest practical length to maximize velocity potential. Is the harmonics issue an overriding concern?

Thanks for the link. It'll be good reading tonight, I'm sure.

 

[IZinterrogator]

I was guessing that you'd want the longest practical length to maximize velocity potential.

Nope, they want the maximum accuracy at a given distance. They don't need to wring out every last bit of speed they can by using long barrels and rounds packed full of powder since they're shooting at a set distance.

 

[Samdweezel05]

I just posted in another thread about this. Long barrels can sometimes cause more problems than they are worth. You have too look at what caliber you are shooting and the distance you will shoot it. Long barrels can give you higher velocity but sometimes you will see pressure problems to gain that velocity. You might end up going with a lighter load to get away from the pressure problems and now you are at the same velocity as you were with the shorter barrel.

Phil

 

[Shane Tuttle]

Nope, they want the maximum accuracy at a given distance. They don't need to wring out every last bit of speed they can by using long barrels and rounds packed full of powder since they're shooting at a set distance.

I can definitely see your point if you're into blackpowder. But, I was under the assumption that if a longer barrel, say 32" instead of 24", would provide "free velocity", then your bullet will sustain supersonic speed easier and longer.

Also, wouldn't higher velocity equate to a flatter trajectory and better at bucking the wind?

Please keep in mind that I'm asking the what ifs, not arguing against your input.

 

[44 AMP]

Longer barrel do yield higher velocities...

But, there is a point of diminishing returns. When you only gain an extra 15fps or so of velocity for an extra inch of barrel, it is worth it?

For any given case and bore size there is an optimum barrel length that can be calculated for a specifc powder. (Don't ask me to do it, but I know it can be done). Most common calibers and powders don't gain enough when you go past 28-30 inches to be really useful. A few of the high intensity large powder capacity rounds could go 32" or maybe a bit beyond before reaching the point of diminishing returns but these are special cases.

Rifles are a balance of features to maximize their performance for specific applications. Long enough to get most of the velocity and short enough to carry in the field goes a long way to determining what the makers offer on production guns.

I've got an old Swedish Mauser (6.5x55mm) with a 29 inch barrel. Sweet shooter, accurate as all get out, gets about all the velocity the cartridge has to offer, but it is a pain to carry around in the woods. Got a Remington 600 in .308 Win. 18.5in barrel. Gives up some velocity, but boy is it handy in the woods. Benchresters have their own needs, varmint hunters theirs, big game hunters their different needs as well. That's why we have so many different guns and barrel lengths available.

I'm not sure what barrel length is needed to reach the point where the bullet is no longer increasing in speed even a tiny bit, but it is both different for each cartridge and longer than practical for field use.

 

[Art Eatman]

Here's a pretty good article about ultimate accuracy and barrel length, for those interested in the closer-in distances, inside 300 yards:

http://www.angelfire.com/ma3/max357/houston.html

I only occasionally read references to barrel lengths of 28" or 30". It appears that most folks who use bolt-actions in the 800- and 1,000-yard competitions use 24" or 26" barrels, commonly.

 

[Jim Watson]

I attend long range competition.
Most of the 24 or 26 inch barrels I see are people trying to get started with standard hunting or wannabe sniper rifles. Dedicated target rifles run to about 30 inches. Mine are only 28 because I did not want to pay extra for longer ones. But then I am not a big league shooter.

One reason is sight radius, the NRA LIKES iron sights. The other is free velocity, so you see long barrels even in the scope classes. A long range shooter is not worried about diminishing returns, as long as there ARE returns.

Requirements for mid range (600 yards) are not as severe as for long range (800-1000) and you would not be unduly hampered by a somewhat shorter barrel. As in the common wannabe sniper rifle. But do not get the 20 inch model meant to go in a patrol car trunk.

 

[Slamfire]

Most of the 24 or 26 inch barrels I see are people trying to get started with standard hunting or wannabe sniper rifles. Dedicated target rifles run to about 30 inches. Mine are only 28 because I did not want to pay extra for longer ones. But then I am not a big league shooter

A common length for the "classic" across the course bolt gun barrel was 26". I have used this length out to 600 yards and it shoots fine.

I also have a 24" barrel in 308, and I like it better than 26" tubes in the standing stages. It is shorter, but weighs the same. Can't tell by my 600 yard scores that a 26" barrel is better than a 24".

Belly shooters, hell, some of them have barrels so long that they leave powder burns on the target from the 600 yard berm.

But extra long barrels are rare. Hard to find storage cases, hard to find front aperatures that open up wide enough.

Look, AMU shooters kick butt with short little 20" tubes on their AR's. What is more important is sight alignment and trigger pull.

 

[Shane Tuttle]

I've got an old Swedish Mauser (6.5x55mm) with a 29 inch barrel. Sweet shooter, accurate as all get out, gets about all the velocity the cartridge has to offer, but it is a pain to carry around in the woods.

This is a pretty good example. I also have a Swedish Mauser. It's the 96/38. The barrel was cut from a 96 to later have the 38 designation. My thought was velocity must have diminished a bit, but I can attest that accuracy compared to my buddy's 96 is the same.

Here's a pretty good article about ultimate accuracy and barrel length, for those interested in the closer-in distances, inside 300 yards:

Thanks, Art. More good readin' for tonight...

Look, AMU shooters kick butt with short little 20" tubes on their AR's. What is more important is sight alignment and trigger pull.

I understand that, Slamfire. But, given the same skills applied to a rifle with longer barrels, is usable velocity gained to benefit precision?

 

[Jimro]

But, given the same skills applied to a rifle with longer barrels, is usable velocity gained to benefit precision?

It depends on if that longer barrel is in fact more accurate. This is when barrel harmonics come into play, longer barrels will have more deflection at the muzzle because they are not as stiff as shorter barrels of the same diameter.

Velocity does not equal precision.

http://optimalchargeweight.embarqspace.com/#/ocwvsladder/4529811360

Jimro

 

[Shane Tuttle]

That's an interesting read. Didn't know the .243 could provide that kind of precision at that long distance.

 

[458winshooter]

Barrels

I just found this article and maybe it will help:www.chuckhawks.com/rifle_barrel.htm there is a _ after rifle FYI

 

[ziggy222]

i read an article where a guy used one gun with a long barrel and tested many loads in it and cut off the barrel in one inch sections and tested all loads each time he cut off another inch.this made the test more accurate since the same gun was tested for all loads.he found that you can't generalize barrel length with performance.if you use a fast burning powder then the powder can be burned before it makes in out the end of the barrel and you will lose some velocity as compared to a slow burning powder that will require a long barrel to get up to its max velocity before the bullet makes it out.in a short barrel the fast burning powder shines and the slow burning powder is'nt all burned before the bullet leaves the short barrel.this leaves powder still burning and flames coming from the muzzle.also if your using a big cartridge with lots of powder in a short barrle you with have a loud boom and flames and burning powder coming from the muzzle and lose velocity.you cannot generalize barrel length.small catridge with fast powder,short barrel.big cartridge slow powder,long barrel.other things come into pay two like bullet weight and harmonics.you can get better patterns with different length barrels but you can also fix that by adjusting your loads or adding or subtracting weight on your barrel without cutting it.barrel weights and the boss system do that.