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Barrel Length and Ammo?

This is a discussion on Barrel Length and Ammo? within the Ruger Double Action forums, part of the Pistol & Revolver Forum category; Is there such a thing as minimum barrel length for .32 HR mag, .327, .38 spl, .38 +P and .357 ammo. I know with more ...


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Old February 4th, 2008, 09:07 AM   #1
 
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Barrel Length and Ammo?

Is there such a thing as minimum barrel length for .32 HR mag, .327, .38 spl, .38 +P and .357 ammo. I know with more barrel length the more in velocity, but what about expansion issues with JHP?



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Old February 4th, 2008, 09:50 AM   #2
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Gunnie 12, A good question and an often overlooked issue when it comes to buying a gun or ammo. First, the barrel length .... when you see specs for a given cartridge, usually they are fired from a gun with at least a 4" barrel. Using reliable chronograph data, you can easily see that shorter barrels loose a lot of velocity. In longer barrel length, the 50 fps/inch rule is normal but in short barrels, velocity loss is way more.

Here's a good example: a 357 Mag revolver with 125 gr JHP factory magnum loads. In a 6" barrel, you can expect 1450 fps, a 4" barrel drops velocity to 1230 fps, and a 2.5" barrel will drop velocity to 930 fps.

Most JHP bullets require at least 1000 fps to get decent expansion in flesh. With the above example, that means 2 3/4" would be minimum length barrel for bullet expansion and because velocity drops considerably at a distance, that 1000 fps MV will go below bullet expansion velocities at 7 yards.

Keep in mind, these are 357 Mag specs ... the other cartridges mentioned will be even worse. You don't buy a snubbie and expect stellar performance. Yes, they go bang and will do a decent job up close but don't look for miracles.
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Old February 4th, 2008, 10:29 AM   #3
 
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Question More Information, Please

Iowegan, I'm not familiar with this rule:

Note: quote edited
Quote:
Originally Posted by Iowegan View Post
Gunnie 12, A good question... In longer barrel length, the 50 fps/inch rule is normal but in short barrels, velocity loss is way more.
Would you elaberate?

Thanx
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Old February 4th, 2008, 01:00 PM   #4
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Jim D, After a certain barrel length, velocity will typically increase about 50 fps for each additional inch of barrel length. Each powder/bullet combination is different but the 50 fps/in rule will be in the ball park. Example: a rifle with a 24" barrel vs a 22" barrel will increase velocity by about 100 fps. It might be 120 fps or 80 fps but it will be close enough to call 50 fps/inch.
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Old February 4th, 2008, 04:44 PM   #5
 
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Wink

"50 fps/in rule will be in the ball park"

I think you got a zero too many

The loss is about 5 fps/in, usually a little less for long barrels.

For instance, the velocity loss out of a 10" vs. a 20" barrel for a .22LR is 39 fps, not 500 fps. The loss for a .308 18" vs. 26" is 32 fps and not 400fps.

However this relationship is not linear. The velocity loss from a 3" vs. a 6" is probaly more than the one you would get from a 10" vs 20" even though both are twice as short and the former is only 3" shorter and latter 10" shorter.

Last edited by nicknitro71; February 4th, 2008 at 04:50 PM.
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Old February 4th, 2008, 07:22 PM   #6
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nicknitro71, You might want to spend a little time at the range with a chronograph.

22 LRs are a major exception to the 50 fps/in rule in rifles but do follow in revolvers under 8". I guarantee you will see more than 39 fps increase from a 10" to 20" barrel. My data shows 1255 fps for a 40 gr 22 LR HV fired from a 24" barrel and 1084 fps from a 10" barrel (both barrels unvented). That's 171 fps difference, not 39 fps as you stated.

"The loss for a .308 18" vs. 26" is 32 fps and not 400fps."

Don't know where you got these numbers but I would challenge them too. A typical factory 308 with a 150 gr bullet will produce 2820 fps from a 24" barrel. That same load will do 2655 from an 18" barrel and 2878 fps from a 26". That's a 223 fps change, not 32 fps. I totally agree .... the velocity will not track to 50 fps/inch across the spectrum of barrel lengths. It only applies to +or- a couple inches from optimum barrel length. In the case of a 308 Win, that optimum barrel length would be 22" (2769 fps) so a 21" barrel (2735 fps) should be about 50 fps slower when in reality it is only 34 fps. The 50 fps/in rule has been used for many years as an estimation and is "close enough" for most shooters to calculate such things as wind drift, bullet drop, and time of flight.

I don't deal in estimations, I deal with real numbers collected from a chronograph or known data charts from factory ammo sources. When I test customer guns, I know what velocities I should get from my loads. If I don't, it usually means there is an issue with the gun.
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Old February 4th, 2008, 09:46 PM   #7
 
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Quote:
Originally Posted by Iowegan View Post
Gunnie 12, A good question and an often overlooked issue when it comes to buying a gun or ammo. First, the barrel length .... when you see specs for a given cartridge, usually they are fired from a gun with at least a 4" barrel. Using reliable chronograph data, you can easily see that shorter barrels loose a lot of velocity. In longer barrel length, the 50 fps/inch rule is normal but in short barrels, velocity loss is way more.

Here's a good example: a 357 Mag revolver with 125 gr JHP factory magnum loads. In a 6" barrel, you can expect 1450 fps, a 4" barrel drops velocity to 1230 fps, and a 2.5" barrel will drop velocity to 930 fps.

Most JHP bullets require at least 1000 fps to get decent expansion in flesh. With the above example, that means 2 3/4" would be minimum length barrel for bullet expansion and because velocity drops considerably at a distance, that 1000 fps MV will go below bullet expansion velocities at 7 yards.

Keep in mind, these are 357 Mag specs ... the other cartridges mentioned will be even worse. You don't buy a snubbie and expect stellar performance. Yes, they go bang and will do a decent job up close but don't look for miracles.
So in effect, a 2" snub loaded with 357 mag 125gr sjhp is problematic in the expansion dept with most ammo at a guesstamated distance of around 5 to 6 yards out of a 2" tube. Is there a 357 round out there that is designed for a 2"? Or in your opinion is one better off with the old stand-by 38 158gr lead swchp and avoid jacketed ammo for the snub?
I do not have access to a chronograph and therefore don't have a clue about velocity obtained for a 2".

Last edited by deputy125; February 4th, 2008 at 10:01 PM.
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Old February 5th, 2008, 05:21 AM   #8
 
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Iowegan,

I still respectfully do not agree. The 50 fps is a gross generalization that maybe only applies to just one and only one interval of length.

Here is a graph showing the relationship between barrel length and velocity loss for a .44 Rem magnum.

It seems that the velocity loss is a function of the negative log of the barrel length.
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Old February 5th, 2008, 05:31 AM   #9
 
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For instance, the loss from 1" to 2" is almost 200 fps but the one from a 17" to 18" is only 10 fps.
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Old February 5th, 2008, 06:36 AM   #10
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nicknitro71, A great chart and an excellent representation of what I was trying to say except the chart numbers are way wrong for a normal 44 Mag load. You want to look at normal barrel lengths ... lets use 7.5" then shorten to 6.5". Based on actual chronograph data, a standard factory load with a 240 gr bullet will run 1272 fps at 6.5" and 1320 fps at 7.5". That's a difference of 48 fps .... not far off from 50 fps. Your chart may be correct if fast burning powder was used but for magnum loads, slow burning powder is the norm. Statistics can be manipulated to get the desired data you want. Good old chronograph data from standard factory loads represent the real results.

Yes indeed, an inch difference with a short barrel makes a lot more difference than an inch at a normal length barrel and an inch difference at extended barrel lengths makes very little difference. As I stated above, the 50 fps/in rule only applies at optimum barrel lengths, not with snubbies or extended length barrels.
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Old February 5th, 2008, 07:31 AM   #11
 
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Actually according to my model the velocity loss from a 6.5 to a 7.5 is 44 fps so we both agree

In the first graph the Y is velocity loss, in the second one Y is actual velocity, that's probably where the confusion is coming from.

Nonetheless, the behavior is logarithmic which it makes sense.
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Old February 5th, 2008, 08:07 AM   #12
 
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What about the 3" SP101 in .38 or .357 – is this sufficient enough? Next, but would be the minimum barrel length for a 22LR revolver – 4”?
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Old February 5th, 2008, 08:28 AM   #13
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deputy125, I know I'll get flack on these comments but here it goes anyway ... Short barreled handguns are intended for ease of concealment, nothing more. It is very difficult to get acceptable bullet expansion performance from a snubby. Lighter bullets stand a better chance of expansion because they are going faster, however, with light bullets, you lose the most valuable attribute .... momentum. The theory is ... if you can't drive a bullet fast enough to expand, use a heavier bullet and take advantage of momentum. What you are trying to achieve is a large wound channel. Hollow point bullets driven fast enough to "open up" do create a larger diameter wound channel. Heavier solid bullets that don't open up create a deeper wound channel. Either is acceptable for the best chance of stopping an attack. Light hollow point bullets that don't open up have a much lower probability of stopping an attack because the wound channel is minimal.

Nearly all 38/357 snubby revolvers have the factory sights registered with 158 grain bullets. Ever wonder why? Wound channel. The optimum load for a 38/357 snubby is a 158 gr solid bullet (no appreciable difference between a lead or jacketed bullet) driven at 38 +P velocities. 357 Mag velocities are better for terminal performance but may be too much recoil.

Basically, a snubby is an "underachiever" in all performance related parameters except concealability. The sights are typically fixed with a poor sight picture, grips don't fit well, accuracy isn't stellar, and recoil is uncomfortable at best. Yes, you can install larger grips for better control but then you lose the intended purpose .... concealability. As mentioned above, velocity is poor too. How many times have we seen a post on the forum about replacing sights or grips on SP-101s? ... and a SP is probably the best snubby on the market.

Most experts agree ... a 4" barrel is optimum for a self defence gun when you take all factors into consideration. 4" GP-100s have adjustable sights (plug-in front sights), good sized grips, heavy enough to absorb recoil, excellent accuracy, and develop enough velocity for ammo to perform well. Granted, the weight and size make it tougher to carry concealed but I found a good high ride belt mounted hip holster works like a champ.

I owned a gunsmith shop for 31 years and sold new and used guns too. I learned a lot about snubbies ... seems there is a fascination with them and always a good market. The typical loop would go like this: a customer wants the lightest and smallest revolver available yet wants it chambered in a cartridge powerful enough to "get the job done". Customer buys a snubby then goes to the range to try it out. Customer returns and wants a "more shootable" snubby ..... better accuracy, bigger grips, better sights, less recoil. After spending money on the snubby and losing concealability, the customer ends up with a 4" S&W 686 or Ruger GP-100. Sometimes there are guns in between. Snubby gets traded in and sold to the next guy. I have actually sold the same snubby revolver as many as four times. With exception of Ruger SP-101s, most snubby revolvers won't hold up to a normal practice regimen .... so I got to repair them fairly often too.

I know this looks like snubby bashing but it isn't intended that way ... more of a factual approach. Does this mean snubbies are worthless? Absolutely not. Sometimes concealability is the driving factor and you just have to deal with the loss of performance. I know I wouldn't enjoy getting shot with a snubby ... no matter how poor the bullet performed.
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Old February 5th, 2008, 08:39 AM   #14
 
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iowegen,
appreciate the thoughts and insights on this subject which leads me back full circle---a 44 spl snub for a larger and heavier bullet and less reliance on expansion. Also gives me warm fuzzy feelings carryng my 45.
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Old February 5th, 2008, 09:40 AM   #15
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deputy125, I totally agree ... bigger is better ... with a 44 or 45 cal bullet, you really don't need bullet expansion to make a large wound channel. Heavy is better ... with any bullet over 200 grains, momentum will work to your advantage and drive the bullet to a deep wound channel, even at slow velocities.

Gunnie 12, I hope I answered your question on the 3" SP. As for 22 revolvers or small semi-autos ... the bullet energy is just not there for decent performance so that is a moot point. Many people (my wife included) won't shoot a gun more powerful than a 22. In those cases, a 22 is certainly better than no gun at all. So you forfeit performance in favor of light recoil, less noise, and cheap ammo. This makes a 22 a great gun where you can practice trigger control, sight picture, handling procedures, and safety without breaking the bank. My wife can shoot her Walther P-22 with amazing speed and accuracy. I sure wouldn't want to be on the wrong end of it, despite the lack of brute strength. Last time we went to the range, she repeatably put 10 rounds in a 1/2 scale body silhouette at 7 yds in just over 5 seconds.
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