How does a longer barrel improve the ballistics of a round

I'm looking to get a hand gun to hunt deer and hogs at Bow ranges...out to about 60yds max.
I want something up to the task but not too bulky to carry.
I'm not interested in a scoped handgun, I like iron sights, and intend to shoot off-hand.
Why is a 6" barrel better than a 4" barrel?
I know the sight radius is better, but how does the longer barrel improve ballistics?

It allows the gas's to build up more preasure behind the bullet, there for increasing power and velocity. This more affected by guns that are fully sealed like autos and rifles as there is a little gas that escapes between the cylinder and barrel but it still makes a difference.

Thanks dc,
is it significant enough to forgo a 4" barrel?

I would say yes for both velocity and accuracy issues. 4 inch is ok but I would not shoot over 40 yards with it. I can hit milk jugs with iron sights every shot with a 6 inch at 100 yards.

Two articles you may be interested in say there is very little difference in velocities related to barrel length. One is on rifles and the other on revolvers/pistols. After reading both articles, I am inclined to say the improved performance of a pistol/revolver with a six inch barrel over a shorter barrel is likely due to the slightly longer sight plane and the additional weight of the weapon which makes it easier to control. Read the articles then, if you have the equipment, try it for yourself and see what you come up with.
http://findarticles.com/p/articles/mi_m0BQY/is_1_51/ai_n7581216 http://www.loadammo.com/Topics/October05.htm

Coastie I don't have the handguns to do the testing but I didn't agree with the one article. He concluded that cylinder gap didn't make a difference when in fact he didn't have the data to determine that. (He didn't have several revolvers of same length and type with different gap) I believe it does and I believe his data shows that it does since the longer barreled revolver had less velocity than the medium length one and a bigger cylinder gap. The longer barrel should show some velocity increase since it doesn't in this instance I would attribute that to velocity loss due to cylinder gap.

4 .004 808 14
5 .006 823 14
6.5 .007 822 16

According to the second article the velocity difference was in the neighborhood of 50 FPS per 2 inch barrel length which changes as it gets longer. Just using that 50 FPS and the numbers given to us the 5 incher should have been clocking in the 830s range and the 6.5 incher in the 860s range. I believe that the chrono numbers show us that there is a loss due to the increased cylindar gap (can't prove or disprove without the proper testing).

As for the semi auto's there could be fundamental differences in lock time and the like. Honestly the way to test this is to have one gun with as long a barrel as one can get on it then cut that barrel down an inch at a time and test away (man I would hate to do such a thing).

tv racin, You may very well be correct. Without doing some extensive research for somebody else, I have no way of knowing what the answer might be. Off the top of my head, I would have to say that at handgun ranges the 100 fps difference in velocities is minimal, almost what you could expect between individual cartridges from the same box of ammunition sometimes and might therefore be ignored. Get a gun you are comfortable with and practice as much as you can afford might be the best advice you can get.

Tv racer is correct. In order to do a scientific test you can only change one factor at a time. Even with a bolt action rifle there will be small deviations of velocity from one rifle of same model to the next. Even with cylinder gap there will be a velocity gain with a longer barrel. If your losing enough gas in front of the cylinder to cause it to be faster at 4 inches than 6 in the same pistol with the same gap you probably have more than manufacture reccomended gap to start with. On a hunting revolver you will not notice a big change in terminal performance with two inches of extra barrel. The largest benefit would be the sight radius. If you have a 4 inch revolver and can shoot it well by all means use it. If you are buying a revolver to hunt with you will probably be happier with a 6 inch. 60 yards is a long way for most of us with a 6 inch revolver. Off hand groups at 60 with a six inch will probably compare well to groups at 40 with a 4 inch.

Coastie I don't have the handguns to do the testing but I didn't agree with the one article. He concluded that cylinder gap didn't make a difference when in fact he didn't have the data to determine that. (He didn't have several revolvers of same length and type with different gap) I believe it does and I believe his data shows that it does since the longer barreled revolver had less velocity than the medium length one and a bigger cylinder gap. The longer barrel should show some velocity increase since it doesn't in this instance I would attribute that to velocity loss due to cylinder gap.

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Well, you've come to the right man, because I have the right equipment. A collection of Dan Wesson revolvers, and a chronograph.

I can set the cylinder gap at anything from .000 to whatever. I carried out this little exercise years ago. Actually when I got my first chronograph.

All of my tests were with maximum loads and heavy bullets in a .445 and .357. The .445 was actually maximum .44 mag loads shooting anything from 240 grains on up. The .357 were maximum loads shooting 158 gr. on up.

There's no question that with big bullets and heavy loads of slow burning powder, cylinder gap makes a big difference. Setting the gap at the from .012 (twice the DW recommended .006) to one half turn off the face of the cylinder. The minimum gap loads would produce bout 150 to 200 fps more velocity. Barrel length seemed to be less a factor, except in some really big boomers with 300 gr. bullets and compressed loads of 296.

So for hunting purposes, I'd set the barrel at a minimum gap. I did this knowing I'd be firing single action, and only firing a couple or three rounds. I wouldn't do this in a carry gun, or on that I was going to fire repeatedly DA.

Supposedly with fast powders and light bullets, the powder has burned before the bullet has completely crossed the cylinder gap, which is why the bullet goes on down the barrel, and all the gas doesn't jet out the gap.

I saw a study on this where someone used strain gauges and high speed photography to correlate bullet position with pressure buildup.

I hunt with my 4" barrel .357 because it's handy. I can keep all my shots in the a 4" circle at 50 yards. The 6 and even 8 inch barrels are more accurate, but not enough to make a critical difference at practical pistol ranges for deer with open sights.

Awesome!!

It would seem the conclusion is any gun you can hit what you aim at with is perfectly fine so long as the caliber is sufficient to do the task.

"Get a gun you are comfortable with and practice as much as you can afford might be the best advice you can get."

I would say that is awesome advice with the small addition of practice with the ammo you intend to hunt with as much as you can afford. Be great to find cheap range type ammo that gives you the same POI as your hunting ammo or carry ammo as the case may be.

The thing about it is that velocity has nothing to do with accuracy.

The things that affect accuracy are: Length of sight plane (the long it is the better you can line up the sights), the trigger (smooth, crisp triggers help the shooter maintain better control of when the shot breaks), lock time (the shorter the better), the throat of the barrel (if it is really long you will tend to lose accuracy), the type of ammunition (if it a bullet type that the gun doesn't like, it won't shoot well).

There are others, but these are the main ones.

The ones that you have control over are the sight plane, the trigger/lock time, and the ammo type.

My recommendation would be at least a 6" barrel if you plan on using open sights out to, and past 50 yards. Get one with a good trigger, or have the trigger worked, and shoot all types of ammo until you find out what your gun likes.

25-06 pretty well sums it up. HandgunHTR makes a valid point as well. Velocity and its variation depend on several factors. They are of little consequence on a 4'' to 6'' revolver at up to 50yds. The important thing is can you shoot it accurately enough and does it have power enough for the job at hand.

If you wrap a piece of notebook paper tightly around the cylinder of a revolver and fire it, you will see how much gas and bullet shavings escape sideways out of the cylinder gap. I am guessing that bullet to barrel alignment is not absolutely perfect and is why some shavings can be found. This situation has to lessen possible velocity a bit.

Regarding cylinder gap; why would you not want that gap to be as small as is possible?

Dave1

why would you not want that gap to be as small as is possible?

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Well, you do, sort of. But that gas and cylinder shavings you are noting with your paper experiment tend to build up on the face of the cylinder and end of the barrel. Also, after a few rapid fire shots, everything heats up enough that minimal clearance makes operation problematic. There also is some runout in the cylinder that has to be accounted for. So to ensure reliable multiple shot operation, the cylinder gap has to be more than the bare minimum.

With the Dan Wesson revolvers I discussed in the previous post, you can lock the cylinder with the barrel if you are mind to do so. You can fudge some on the DW recommended gap, but if it's too tight the gun won't function reliably.

I guess I'll butt in with my opinion. One reason accuracy is better with the longer barrel is the time the bullet is engaging the rifleing. Up to a point the rifling will stabilize the bullet better. Now I'm not sure of where that point is but I'm convinced that 4 in barrels have not the length to fully establish the proper spin on the bullet. Having shot 4in guns and six in guns I'd say the six in guns are more accurate. I imagine that 10 or 12 inches is even better for estabishing the spin. Just my 2 cents worth.