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Old October 28, 2008, 02:57 PM   #1
jamaica
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Barrel Length/Velocity In Revolvers

Is there really much difference in velocity due to barrel length in revolvers?
As soon as the bullet is in the barrel, the gas escapes out the crack between the barrel and the cylinder reducing the pressure. I find it hard to believe that there would be much difference in velocity from a 4" barrel to a 7.5 inch.

Have any of you had occasion to test a load in different revolver barrel lengths with a chrono?
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Old October 28, 2008, 04:17 PM   #2
saudst
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Velocity loss

Jamaica,

Yes, the gas does escape from the barrel cylinder gap, but not enough to make a huge difference, but some. Generaly on hand guns you lose about 15-25fps. per inch depending on the load and firearm used, about 30-40fps. on high powered rifle loads to a certian piont. I have done crony testing on my 2 45/70s, one with a 24" tube and one with a 30" and there is a big difference.

I have also read an article where a writer took a 10" Ruger and test fired in between cutting an inch off at a time and this is where I get the 15-25fps. figure but there are so many variables( chamber tightnes, bore condition, powder burn rate) that you may get the same velocity with barrels an inch or two apart, but the fact is that the bigger seperation in length there is, the higher the velocity you will have with the longer barrel. Your comparison has 3.5" in difference. it is even more of a increse when you compare a snub nose to a 7.5"er. At the end of the day, the longer the bullet is being exelerated ( i.e. a longer barrel ), the higher the velocity for the same load.

The difference in your senerio may be 45-65 fps., not that much if you have other considerations like portability ect.. I hope this helps.
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Old October 28, 2008, 04:25 PM   #3
AlaskaMike
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Saudst is right. The barrel/cylinder gap does cause you to lose some pressure and velocity, but even with that, the velocity increases with longer barrels is an easily proven thing.

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Old October 28, 2008, 04:51 PM   #4
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Yes, length of revolver barrel makes a difference in velocities. Below is one example of the same load being shot in four revolvers (three different barrel lengths) thru Oehler M34 chronograph. Velocities are averages of 5 shot strings. Revolvers 3 and 4 are identical models.
Load: 23 gr/H110/250 cast H&G bullet
Revolver 1: S&W M629, 4" barrel = 1131 fps
Revolver 2: S&W M629, 6" barrel = 1271 fps
Revolver 3: S&W M629 Classic, 6.5" barrel = 1296 fps
Revolver 4: S&W M629 Classic, 6.5" barrel = 1321 fps
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Old October 29, 2008, 10:51 AM   #5
jamaica
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OK, that helps. Thanks everyone.

I guess that blast out the side doesn't reduce the pressure completely. I'll tell you what though, if you ever have any part of your body near the front end of the cylinder when you cut loose, you would think it all came out there.

I keep thinking about a Ruger Blackhawk 44. I want one with a Bisley grip frame and 5.5 inch barrel. I like that barrel length for the convenience of carry. The 7.5 inch barrel would be great for shooting, but since I carry a gun much more than I shoot it, the shorter barrel suits me fine. I guess I would take a bit of velocity loss, but it won't be critical.
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Old October 29, 2008, 09:24 PM   #6
drail
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Search for and find a Bisley. Much more pleasant to shoot in .44 Mag than a Blackhawk.
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Old November 1, 2008, 09:33 AM   #7
MADISON
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Barrel length and velocity

You loose:
30 fps when the maker uses a real gun for their figures.
75 fps when the maker uses a universal receiver for their figures
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Old November 1, 2008, 12:21 PM   #8
Peter M. Eick
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Be very careful accepting conventional wisdom of longer barrels are faster then shorter barrels. The following is real data all 158 grn cbc LSWC commercial ammo. All 50 round strings over the chrono.

38/44 6.5" barrel 696 FPS
38/44 5" barrel 704 fps
Pre-27 8 3/8" barrel 683 fps
Diamondback 4" barrel 723 fps
Detective special 2" barrel 651 fps.

So from this experiement, I could reasonably claim that the optimal barrel length for this ammo is 4" and dropps accordingly with longer barrels and shorter barrels.

You could also claim that a 2" barrel is just about as fast as an 8 3/8" barrel.

I could point out that you lose about 20 fps per barrel inch past 4" or I could say you gain 25" fps per inch less then 4".

Anyway, you can see my point. Rules of thumb are not accurate when it comes to velocities. Get a chrono and be sure.

As a final thought my pre-27 8 3/8 is just slow in general and my colts tend to be fast in general.
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Old November 1, 2008, 12:35 PM   #9
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Peter,

I think what your particular examples demonstrate is that there are a number of variables that affect the final velocity of a particular load. Barrel length is just one of them. Others might be cylinder/barrel gap, barrel diameter, chamber diameter,...and so on

I don't think your conclusion regarding the load is valid because you didn't (couldn't) control the other potential variables when testing that load in a variety of different guns.

In order to determine the 'optimum' barrel length for a load (in terms of velocity), you'd almost have to use a single gun, cutting the barrel between each test string and checking the results.

Even this would be of questionable use, since the optimum barrel length may (almost certainly does) vary from gun to gun for a particular load.

Of course the other problem with determining your optimum barrel length by cutting down a single gun, is that by the time you've figured it out, you've already chopped the gun too short.

Given the notable velocity increase in carbine's chambered for most handgun rounds, I'd venture to guess that ANY of the handguns you listed would demonstrate higher velocities if you screwed on longer barrels.
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Old November 1, 2008, 03:16 PM   #10
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"I guess that blast out the side doesn't reduce the pressure completely.'

Right. Something from an engineering point of view, the high presure of the propellant gas is also quite dense. That means the forward flow of the dense, high speed gas keeps it sorta "focused" on the base of the bullet. It has a harder time turning to exit the cylinger gap that it first appears.

How much velocity we gain or lose per inch of barrel depends a LOT on the load itself; the time/pressure curve makes a difference. Generally speaking, we gain more speed with long barrels if we use a slower powder, while short barrels loose less speed per inch of barrel if we use faster burning powders.

That said, there is a common perception that we should get higher speeds from short barrels if we use faster powders; that's not true. The powder that gives the best velocity with any given bullet will do so reguardless of the lenght of the barrel. But, the ear-splitting muzzle blast of loads with slow powders fired from short barrels is much higher because the bore pressure at the moment of bullet exit is higher. Again, it's the time/pressure curve of the load that counts.
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Old November 1, 2008, 07:47 PM   #11
Peter M. Eick
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Musher,

You could make any of the claims I made from the data or the claims you made. Either is valid.

My point was that 'in general' don't trust arbitrary rules of thumb for velocity relationships to barrel length. I have seen too many variations to trust any rules.

Without getting into more data, I have a fast Pre-27 8 3/8 and a slow pre-27 8 3/8. Cylinder gap is the same but one has been highly polished and worked over. The barrels and cylinders are nearly identical sized and dimensioned. The main difference is the highly polished one is slow regardless of the load.


I have seen the same problems with my 38/44 5" hd's. I have an absolute bunch of them now and this picture is way out of date.



If I take the same load and chrono them out of say 5 or 6 pre-war 5" HD's. I will get at least 100+ fps variation in the velocity. Not sure why but I have eliminated throat diameter (bought a pin die set to prove that) barrel diameter (slugged most of the barrels now) and cylinder gap (used some washers to bring them into the same diameter. I am now conjecturing that it is due to the roughness of the bore or that the chambers are different sized. So I am still working on it.

Fun discussion. Take care folks.
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Old November 1, 2008, 11:15 PM   #12
musher
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Sorry I didn't express myself clearly Peter. I was responding to your statement that for that particular ammo, you had determined an optimal barrel length.

All I was trying to say is that you couldn't really draw any conclusion about the ammo, given the testing as you described.

Sweet bunch of hd's and outdoorsmen (mans?)
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Old November 2, 2008, 11:55 AM   #13
Peter M. Eick
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Yes they are Outdoorsmans models. I now have 5 or 6 of them. I hate to say it but I have lost track. I tend to only keep track of my two shooters, a post war and a pre-war and the rest just a locked up. Same with my heavy Dutys. I now have finally picked up a shooter pre-war 4" 5" and 6.5" that I will use for an experiment but in the mean time I have accumulated a bunch of other HD's that are more just as backups or caught my interest at the time.

Great guns but good ones are getting very expensive!
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Old November 2, 2008, 01:39 PM   #14
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I once experimented with 45acp 200gr SWC ammo out of my 5'' 1911 and my Taurus model 455 45acp revolver with a 6 1/2'' barrel.

My 5'' 1911 averaged 968fps

and my

6 1/2'' revolver averaged 1033fps all shooting the same ammo.

This proved to me the gas loss out of the barrel/cylinder gap is negligible in terms of making a difference in performance.
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Old November 3, 2008, 06:40 PM   #15
Gun 4 Fun
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Peter, I was looking at you load/velocity data and I don't know what type of powder or charge weight you were using but I believe that it is a mild or target type load. Well, I guess in .38 it's pretty much factory equivalent. the point is, lighter loads with fast burning powders peak out on pressure earlier in the barrel, and as a result they tend to stop pushing as hard/long as a slower powder,thus the barrel itself becomes a drag on the bullet lowering the velocity. If you went to a slower powder and heavier charge weight, I believe the longer barrel would give the higher velocity. Don't misunderstand, I got your point on the fact that there are no hard and fast rules, this is merely an observation from 35 or so years of loading for, and shooting a wide range of guns.
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Old November 3, 2008, 07:26 PM   #16
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velocity loss.

Musher, Gun4fun.

My point exactly. There are a lot of other variables, but barrel length to a point is related to velocity. You guys nailed it.
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