Interpolate new FPS & NRG per barrel length?

[PT7]

Would like to find out if there is a formula to determine certain ammo stats based on a longer-length barrel? I have a .357 Magnum round that shows testing done with a 10" barrel. I'd like to see if stats are much different for use in my Henry AW with a 20" barrel.

Here are the stats I've found for this ammo:

Caliber: .357 Magnum
Weight (Grains) 158
Mzl Vel (fps) 1560
50yd Vel (fps) 1434
Mzl NRG (ft.lb) 865
50yd NRG (ft.lb) 722
Barrel Length 10"

PT7

[GunnyGene]

A general "rule of thumb", is 25fps per additional inch of barrel. I'm not aware of any broad formula that will give an exact number, since there are many other factors that are specific to the individual firearm. Also see this: http://www.ballisticsbytheinch.com/

[PT7]

Appreciate the "rule of thumb," Gunny. I'm looking mainly for an estimate.
Thanks for the BBTI link. Looks like there is some interesting stuff there...will check it out for sure.

PT7

A general "rule of thumb", is 25fps per additional inch of barrel. I'm not aware of any broad formula that will give an exact number, since there are many other factors that are specific to the individual firearm. Also see this: http://www.ballisticsbytheinch.com/

[wingnut]

Approximation done with QuickLoad & QuickTarget. BTW, that is a very hot load even with Win 296 & A2400, ~37.6K psi vice 35K psi SAMMI.

Code: Select all

10 in bbl
Gun / Ammunition : .357 Magnum (SAAMI)
 Bullet Type      : .357, 158, Nosler JHP 44841
 Bullet Weight    : 158 grains or 10.24 Grams
 Muzzle Velocity  : 1564 fps
 Twist Length     : 38.0 in.  (RH)
 Gyro.  Stability : 0.61
 Crosswind Speed  : 10.0 Mph 
 Ballistic Coefficient(s) (G1) :
 C1_1=0.182@V>0 fps;

 Optimum trajectory information : 
 Optimum sight-in range (X) = 120 Yds. 
 with max. ordinate above LOS at range (M)= 66 Yds.
 and max. point blank range (P)= 141 Yds.
-------------------------------------------------------------------------------------
 Range  Velo Time of  Energy   Path   Spin / Wind-  Total  Sight correction  Target
        city  flight            to     dage, Wind    drop   for setting new   lead
                                LOS    of 10.0 Mph             zero range     33 fps
-------------------------------------------------------------------------------------
·Yards   fps     s    ft.lbs.   in.    in.     MOA     in.   Clicks     MOA     yds ·
-------------------------------------------------------------------------------------
|    0  1564  0.0000    858    -0.8    0.0   -----     0.0   ------    -----    0.00
|   25  1478  0.0487    767    +1.1   -0.1   -0.48     0.4    -11.6    -4.00    0.53
|   50  1399  0.1008    686    +1.9   -0.8   -1.59     1.9    -10.3    -3.54    1.10
M   56  1380  0.1139    669    +1.9   -1.1   -1.86     2.4     -9.3    -3.21    1.25
|   75  1325  0.1562    616    +1.6   -2.1   -2.67     4.5     -5.7    -1.95    1.71
X  100  1257  0.2141    555     0.0   -3.8   -3.62     8.2      0.0     0.00    2.34
-------------------------------------------------------------------------------------
M = Peak vs. L.O.S, X = Set Zero, P = Max. Point Blank Range
Elevation above Angle of Site (0.0 deg.)  = 0.1431 deg.


20 in bbl
Gun / Ammunition : .357 Magnum (SAAMI)
 Bullet Type      : .357, 158, Nosler JHP 44841
 Bullet Weight    : 158 grains or 10.24 Grams
 Muzzle Velocity  : 1749 fps
 Twist Length     : 11.0 in.  (RH)
 Gyro.  Stability : 7.56
 Crosswind Speed  : 10.0 Mph 
 Ballistic Coefficient(s) (G1) :
 C1_1=0.182@V>0 fps;

 Optimum trajectory information : 
 Optimum sight-in range (X) = 132 Yds. 
 with max. ordinate above LOS at range (M)= 74 Yds.
 and max. point blank range (P)= 155 Yds.
-------------------------------------------------------------------------------------
 Range  Velo Time of  Energy   Path   Spin / Wind-  Total  Sight correction  Target
        city  flight            to     dage, Wind    drop   for setting new   lead
                                LOS    of 10.0 Mph             zero range     33 fps
-------------------------------------------------------------------------------------
·Yards   fps     s    ft.lbs.   in.    in.     MOA     in.   Clicks     MOA     yds ·
-------------------------------------------------------------------------------------
|    0  1749  0.0000   1073    -0.8    0.0   -----     0.0   ------    -----    0.00
|   25  1656  0.0446    962    +0.7   -0.3   -1.01     0.4     -7.9    -2.73    0.49
|   50  1566  0.0913    860    +1.4   -0.8   -1.59     1.6     -7.7    -2.64    1.00
M   58  1538  0.1066    830    +1.4   -1.1   -1.77     2.1     -6.8    -2.33    1.17
|   75  1480  0.1400    769    +1.2   -1.7   -2.15     3.6     -4.4    -1.52    1.53
X  100  1400  0.1920    688     0.0   -3.1   -2.93     6.6      0.0     0.00    2.10
-------------------------------------------------------------------------------------
M = Peak vs. L.O.S, X = Set Zero, P = Max. Point Blank Range
Elevation above Angle of Site (0.0 deg.)  = 0.1172 deg.

I hope that is close enough. Different bullet shapes will produce different bullet BC's that will produce different elevation drops, V drops at range & E drops at range.

[GunnyGene]

Appreciate the "rule of thumb," Gunny. I'm looking mainly for an estimate.
Thanks for the BBTI link. Looks like there is some interesting stuff there...will check it out for sure.

PT7

A general "rule of thumb", is 25fps per additional inch of barrel. I'm not aware of any broad formula that will give an exact number, since there are many other factors that are specific to the individual firearm. Also see this: http://www.ballisticsbytheinch.com/

You're very welcome. Also, what wingnut posted is a better estimate than the "rule of thumb". Ballistics is a very complex subject, but if you're interested, here's a couple video's from TiborasaurusRex in his Sniper 101 series, beginning with Part 25. His primary focus is on ELR (Extreme Long Range) shooting, but the basic principles apply across the board.

https://www.youtube.com/watch?v=F39yUEM ... ex=26&t=0s

1. Internal Ballistics -- and all the possible factors that cause variations in either MV or in Point of Aim as the bullet begins its motion and how to correct for them. • We will discuss the nature of propellants and how they affect projectile movement / pressures • We will discuss different factors that can affect the MV of a projectile o Variations in ammunition / reloading tips / non-uniformities -- propellant moisture, primer seating, bullet seating, case dimensions, powder weight, orientation of grains in a case, projectile weight/profile, etc... o Tolerances in different weapons o How bore wear affects muzzle velocity o Propellant Temperatures o Projectile and Bore Temperatures o Coppering o Powder Fowling o Bore conditioning and barrel memory • We will talk about how other factors can cause the axis of the bore at the breech to differ slightly from the axis of the bore at the muzzle o Muzzle Jump variations due to inconsistent rifle deployment -- bipods vs sandbags, deployment and marksmanship techniques o Whip action - harmonics o Deflections due to muzzle break pull-off. o Other tips

2. Intermediate ballistics -- we will mention how suppressors effect the transition of the projectile from internal progression to external flight '

3. External Ballistics -- is the science of all the factors that affect the flight path of the projectile after its exits the muzzle. • We will discuss everything you will need to know: how changes in ambient air temperature, humidity and barometric pressure affect the bullet. We will talk about wind, how to set up Microsoft excel to make corrections for coreolis effect, how and why spin drift occurs and much much more.

4. Terminal Ballistics -- is the study of what happens once the projectile arrives at its destination.

[PT7]

Thanks to both.
Yeah, complex is the word for it.

Cannot imagine the computer work and effort needed to create a bullet for a specific purpose, e.g. the Hornady ELD-X bullet created three years ago. And their initial offerings came in three calibers with 7 bullet weights across those calibers. What was needed to achieve their goal is beyond me. To think those basic stats of weights & calibers were only the tip of the tip of the tip, etc....of the iceberg.

Appreciate all the info you sent.

PT7

Approximation done with QuickLoad & QuickTarget.
I hope that is close enough. Different bullet shapes will produce different bullet BC's that will produce different elevation drops, V drops at range & E drops at range.

You're very welcome. Also, what wingnut posted is a better estimate than the "rule of thumb". Ballistics is a very complex subject....

[GunnyGene]

Thanks to both.
Yeah, complex is the word for it.

Cannot imagine the computer work and effort needed to create a bullet for a specific purpose, e.g. the Hornady ELD-X bullet created three years ago. And their initial offerings came in three calibers with 7 bullet weights across those calibers. What was needed to achieve their goal is beyond me. To think those basic stats of weights & calibers were only the tip of the tip of the tip, etc....of the iceberg.

Appreciate all the info you sent.

PT7

Approximation done with QuickLoad & QuickTarget.
I hope that is close enough. Different bullet shapes will produce different bullet BC's that will produce different elevation drops, V drops at range & E drops at range.

You're very welcome. Also, what wingnut posted is a better estimate than the "rule of thumb". Ballistics is a very complex subject....

And to think the basis of modern ballistics started with Niccolò Tartaglia in 1531, although he continued to use segments of straight-line motion, conventions established by Avicenna and Albert of Saxony, but with the innovation that he connected the straight lines by a circular arc. Then followed up by Galileo in 1638 (parabolic motion), and Newton in 1687 with his Principia Mathematica which gave us the laws of gravity & motion. We've come a very long way since then. Gives an appreciation of what goes into making a shot @ 3 miles as was done recently.

[North Country Gal]

What I've found over the years shooting revolver/pistol rounds in my Contenders is that the velocity gain/loss is not consistent across a wide range of barrel lengths, so formulas based on fps loss for each inch of barrel can only be carried so far. In the case of the 357, you're only going to squeeze so much velocity out of the cartridge, beyond which add more barrel length has no effect or even begins to show a velocity loss.

Here's great resource on the 357, for instance, showing that the velocity gain by going to a 20" barrel from a 16" barrel is not that much.
http://www.ballisticsbytheinch.com/357mag.html

For an autoloading pistol cartridge like the 45 ACP, which I shoot in both a 10" and 12" barrel on my Contender, note how little is gained over shooting the 45 ACP in one of my 1911s with a 5" barrel.
http://www.ballisticsbytheinch.com/357mag.html

[North Country Gal]

Those of us who have been shooting Contenders for years know very well that cartridge design is the biggest factor in which cartridges do well in a 10" barrel and which cartridges need a 14" barrel to be most effective. In fact, in the early days, some cartridges were actually invented to be best used in a 10" barrel.

A classic example of a rifle cartridge being a mismatch for a 10" barrel is the 222 Remington. When Remington shocked the world with their revolutionary XP 100 bolt action pistol, back in the mid 60s, the prototypes were originally chambered in the 222. What Remington quickly discovered was that the 222 was a very inefficient cartridge in the 10" barrel of that first XP. Simply put, that 10" of barrel length was not enough to burn all the powder in a 222 case. Remington then shortened the 222 case, little by little, reducing the powder capacity until they found the most efficient capacity in a 10" barrel. This "222 Short", so to speak, was given the name, the 221 Fireball. Interesting cartridge, the 221. In a 10" barrel, I get the same velocity with the 221 as I get with my 10" 222 Contender barrel, even though the 221 Fireball (222 Short) uses less powder. On the other hand, when I go to a 14" 222 barrel on my Contender, the 222 is much more at home.

[clovishound]

The easiest and most accurate way to determine this, is to get a friend to let you use their chronograph. A couple shots through the crony will give you the skinny.

FWIW, I ran a 158 grain soft point American Eagle through my 20" BBS. Box said 1240 fps out of (presumably) a revolver barrel. Chrony said it was 1800 fps. I'm sure the burn speed of the powder in a .357 will make a big difference in the change in MV from a short barrel to a long barrel. I doubt I would gain much from a fast Titegroup load vs a slow H110 load. I'm sure most of the .357 factory loads are going to use slower powders to maximize MV in revolvers. There may be a few out there that are optimized for short barrels, but will probably be advertised as such.

BTW, Hogdgon has data for both pistol and rifle in .357. If you want you can compare the difference of the same load from a short barrel, and a long barrel. Again, without knowing the powder used in a factory load, you will still be making a WAG.