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  #1  
Old 04-25-2006, 04:49 PM
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Optimum Barrel Length


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I have seen various posts about barrel length in relation to muzzle velocity and muzzle energy. Most generally, the discussions say longer barrel, more "punch", but I saw a post (not sure if it was this forum) that a guy with a 16" 22LR that chrono'd faster and was harder hitting than 20" or 24" 22LR barrels. It seems to make since that a 22 would start slowing down in a longer barrel because of the powder all being burnt before the bullet exits. Of course, this would be affected by the powder loads, but I was wondering if any testing has been done on different calibers to figure out what optimum barrel length for each caliber would be?
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Old 04-25-2006, 05:02 PM
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This barrel length would depend on what ammo you would be using and what the speed was. I know that most .22 bench guns have a barrel length of about 20". That is with ammo going about 1050fps. Faster ammo like CCI mini mags I would think would do better in a longer barrel. I am not 100% on this, but just makes sense to me. Main thing is the speed of the ammo you want to use. Would be nice to have an old barrel to test. If I had one this is one test I would like to know what that magic length is.

Just a thought, was that other post you saw talking about just best speed, or accuracy? I would want a length that was the most accurate, not the fastest.
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  #3  
Old 04-25-2006, 05:07 PM
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Quote:
Originally Posted by Gismo
This barrel length would depend on what ammo you would be using and what the speed was. I know that most .22 bench guns have a barrel length of about 20". That is with ammo going about 1050fps. Faster ammo like CCI mini mags I would think would do better in a longer barrel. I am not 100% on this, but just makes sense to me. Main thing is the speed of the ammo you want to use. Would be nice to have an old barrel to test. If I had one this is one test I would like to know what that magic length is.

Just a thought, was that other post you saw talking about just best speed, or accuracy? I would want a length that was the most accurate, not the fastest.

Someone with their copy of Hatcher's Notebook might look it up...but remember that his estimation of a 30-06 (and this was with the faster powders used in the 1930's and 40's) wouldn't stop shoing a gain in velcoity until the barrle was somthinglike 3 yards long.

The .22LR burns somthing like 1.8gr.- 2.2gr. of powder...it takes 16" of barrel for this tiny cahrge to peak out.

Waht isn't fair is comparing differnt barrels...wuld need ONE barrel, really long, cut back in seps to get meaningful data. I've had identical lengths (22") give widely differing velocity readings with the same ammo.


"Magic" length? Max. vel. does not have to equate to max. accuracy.
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Old 04-25-2006, 05:17 PM
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Quote:
Originally Posted by Kansas
I have seen various posts about barrel length in relation to muzzle velocity and muzzle energy. Most generally, the discussions say longer barrel, more "punch", but I saw a post (not sure if it was this forum) that a guy with a 16" 22LR that chrono'd faster and was harder hitting than 20" or 24" 22LR barrels. It seems to make since that a 22 would start slowing down in a longer barrel because of the powder all being burnt before the bullet exits. Of course, this would be affected by the powder loads, but I was wondering if any testing has been done on different calibers to figure out what optimum barrel length for each caliber would be?

Even if the powder is all spent, you still have a great amount of pressure behind the projectile. Remember, powder burning creates pressure, the air expands and that pressure pushes the projectile. That is the reason that reloaders control the pressure by using powders that burn at different rates. I guess it is possible that a shorter barrel could produce faster velousities, but 16 to 20 inches the 20 should produce better velousity. As far as the best for each caliber, I beleive you loose about 100 FPS for each inch a barrel is shortened, as a generic number. I hunt w/ some 24", some 22", and some 18" barrels. I can bet you the game does not know the difference. Shoot what you are comfortable with. There is no best in anything when it comes to most firearms. JP

Last edited by jpattersonnh; 04-25-2006 at 05:20 PM.
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  #5  
Old 04-25-2006, 05:24 PM
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I was going to be a smart @$$ and say "27' but it's not very practical".... but I see Ribbonstone once again beat me to it...only he's serious....now that's the scary part! LOL

Was going to buy a .375 H&H one time w/ a 34" barrel. Very good accuracy, didn't chrono it but the POI with my handloads was exactly 2" higher at 200 yds than the factory loads...same difference from the 26" barrel one I already had. Definitely not scientific but if there was any velocity gain from the extra barrel length, it wasn't showing any on the POI.
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Old 04-25-2006, 06:53 PM
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Remember he also calculated the weight of the breech block needed for a blow back 30-06...but don't remember the exact weight (other than it was more than you'd care to carry around).

Do belive that velocity will show as gain until the point where bullet friction's value is greater than gas expansion. When comparing differnt rifle barrels, would have to have the same friction value...which is darned hard to figure out.


But therre should be a "ball park" figure out there for cases burning 30gr. of pwoder or more. I prefer to figure the following:

Velocity will increase or decrease by something between 1/3 and 1/2 the PERCENTAGE of length change.


Why the percentage?

Adding 2" to a 20" barrel has more vel. value than adding 2" to a 33" barrel.

Would guess that making a new ball-park-estimator using barrel volume would be more impressive...but i can't work those out in my head like I can with just lengths (and as volume and length would be proportional, don;'t guess it matters much).

Last edited by ribbonstone; 04-25-2006 at 06:56 PM.
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  #7  
Old 04-25-2006, 06:57 PM
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Hatcher only lists 4 barrel lengths.

24" = 2700

32" = 2848
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  #8  
Old 04-25-2006, 07:11 PM
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It is a common sense thing. At any given bore dia., the more case volume the longer the bbl need to maximize the velocity. Example 308 Win will max about 20 to 22 inchs, the 300 RUM will max about 26 to 30 inches.
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  #9  
Old 04-25-2006, 07:12 PM
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Quote:
Originally Posted by kenh
Hatcher only lists 4 barrel lengths.

24" = 2700

32" = 2848
Thanks...don't remember what book I read it in (and the books are gone) be belive it was one of Hatcher's.

Still, think the idea here is that there shuld be a gain in velocity long after you've past the reasonable length for human carry.
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  #10  
Old 04-25-2006, 07:41 PM
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But you do not. You are forgeting the friction between the bullet and the bbl.
I recall a test with 4 different 308 Win loads and a bbl starting at 26" and cut back a 1" segments. Average velocity CAME UP from 26" to 24" then changed very little from 24" to 22", showed a slight drop from 22" to 20" and moderate drop from 20" to 18".
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  #11  
Old 04-25-2006, 08:21 PM
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Quote:
Originally Posted by Jim Rau
But you do not. You are forgeting the friction between the bullet and the bbl.
I recall a test with 4 different 308 Win loads and a bbl starting at 26" and cut back a 1" segments. Average velocity CAME UP from 26" to 24" then changed very little from 24" to 22", showed a slight drop from 22" to 20" and moderate drop from 20" to 18".
Yea, that is the kind of info I am looking for. As pointed out before, It has to be done with one barrel with 1 load and would be different in a different barrel with a different load, I know. But it would give you a ballpark to look for.
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  #12  
Old 04-26-2006, 12:59 AM
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Thumbs up

This was a test done several years ago by the late (Great) Bob Melik (SP) and it was very informative.
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  #13  
Old 04-26-2006, 03:45 AM
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Have been several tests of this type, problem being that none of them seem to be in total agreement. That should be expected as barrels seldome agree about loads.

Think the important things from all the tests I've seen are that:

1. different loads (becasue of the differnt powders used) vary more or less with barrel length.

2. the vel. gains past a certain point, while still there, are minor.

3. IN GENERAL, the more powder being burned, the more effective a long barrel.

4. that there seems to be at least 5variables at work: powder charge, barrel volume, friction,pressure generated, and powder burning speed.

Last edited by ribbonstone; 04-26-2006 at 03:47 AM.
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  #14  
Old 04-26-2006, 07:42 AM
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Agree with ribbonstone, particularily the last (#4) item.

All these variables must be considered when trying to determine optimum velocity for a particular cartridge.

The old military rifles had barrels of 28" to 32" with this aspect in mind. I've got several what I consider "high performance" rifles that have 27" barrels for the purpose of wringing out as much velocity as possible for the given cartridge. Wouldn't want to try using them in thick brush type hunting, but they aren't too awkward stand hunting or out here in the open West.
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Old 04-26-2006, 01:53 PM
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Isn't a slightly shorter barrel also more likely to be accurate, as the harmonics of the barrel play with shorter barrels less than longer barrels? I believe most rifle and barrel manufacturers have given us the best compromise, the magic length is 22-26"
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Old 04-26-2006, 02:28 PM
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I've found that if I use an average of roughly 50 fps it seems to be fairly close in most of my rifles. I think optimal may be different for different calibers and I couldn't tell you what makes that difference. For the 270 Win for instance, I think optimal is 24". Both Ken Waters and Jack O'Connor found that there was 100+ fps gain over a 22" barrel. A thread on another forum talked about this a while back also:

http://www.thehunterslife.com/forums...ead.php?t=3050
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Old 04-26-2006, 02:42 PM
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According to this very interesting article -----> http://www.marlinowners.com/board/viewtopic.php?t=11886

The magic length for accuracy is 21 3/4".
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Old 04-26-2006, 03:12 PM
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Quote:
Originally Posted by kdub
Agree with ribbonstone, particularily the last (#4) item.

All these variables must be considered when trying to determine optimum velocity for a particular cartridge.

The old military rifles had barrels of 28" to 32" with this aspect in mind. I've got several what I consider "high performance" rifles that have 27" barrels for the purpose of wringing out as much velocity as possible for the given cartridge. Wouldn't want to try using them in thick brush type hunting, but they aren't too awkward stand hunting or out here in the open West.

I've been wondering about that.

Didn't find a whole bunch of short barrled muzzle loaders...but they managed to sneak through the woods and hunt with those 40" - 44"full stocked long guns or the 28-32" Hawken types. Oddly, the later plains/Hawken types rifles (wee there isn't much bursh) were shorter than the earlier long rifles (used mostly in th woods).

You'd have expected the opposite, at least by today's standards.

After a few seasons of bow hunting, come to realize ANY rifle gets through the woods better than a bow.
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Old 04-26-2006, 03:34 PM
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Quote:
Originally Posted by mattsbox99
Isn't a slightly shorter barrel also more likely to be accurate, as the harmonics of the barrel play with shorter barrels less than longer barrels? I believe most rifle and barrel manufacturers have given us the best compromise, the magic length is 22-26"

Now that brings up a very important, and valid point. Barrel Harmonics! What does that mean? Well ( for you younger guys and others) when a gunsmith was making barrels he would finish the barrel, but not to finished length. The barrel w/ action attached was then fitted to a vise (action only). A plate of glass was then layed over the barrel and covered w/ a light coat of very fine sand. When it was fired, a pattern would be visible on the sand. Where the pattern intersected the barrel were the points of best accuracy. Varying the thickness of the steel will effect where the lines intersect the barrel. I have some very old books that touch on this technique. Now they use computers. Sorry, just wanted to add this. Did not mean to rant! JB could explain it better, it is the same as the vibration of a Guitar string. JP

Last edited by jpattersonnh; 04-26-2006 at 03:37 PM.
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  #20  
Old 04-26-2006, 05:57 PM
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Quote:
Originally Posted by KenK
According to this very interesting article -----> http://www.marlinowners.com/board/viewtopic.php?t=11886

The magic length for accuracy is 21 3/4".
That article is talking about the 22PPC. I believe he is wanting to know about the .22LR barrel length.

Never mind. My mistake. He is wanting info on different calibers as well.

Last edited by Gizzy; 04-26-2006 at 06:00 PM.
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