Energy vs Velocity vs Barrel Length

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Eric Larsen

New member
I had checked this issue out because I carry a 357 snubbie and was curious how much the shorter barrel actually lost...kinda interesting.

Victims in the test: 158 gr Speer Gold Dots 357
S&W m27 5" barrel
Ruger sp101 2.2" barrel

5" velocity was 1314 FPS with FPE @ 605
2.2" velocity was 1022 FPS with FPE @ 366

The velocity was 29% more from the longer barrel and had 65%
more energy. Thats alot.

Even though the snubbie lost ALOT of energy...the plus is its still
almost 2 times what 38 +P does from the same barrel...top rounds are in the 200 FPE range.......

Shoot well
 
Eric,

Thanks for posting the info.
It's always good for us to post our results on this BB to add to our collective knowledge (for future reference).
 
CURVING THE "WHAT IF"

What if we tested a 'slow' six-inch, or a real fast four-inch? Or a really really fast 2.5"?

How about we test IN OUR GUN, and make better assumptions?


Naaaaaah...............
 
Lot of difference from gun to gun.
Specially in the snubbies. Not unusual to find 200 fps difference with same ammo fired in conscecutive numbered identical snubs.

Info from other's guns gives us a ballpark idea of performance to expect from our guns.

Like WS2 says.....you never know for sure till you chrono your own.

Sam
 
A more conclusive test would involve starting with a eight inch barrel, then begin cutting the barrel back in increments of one or two inches.
 
The 8'' bl. idea sounds great. Lets do it with class. Who wants to donate a Python for the chopper. When we get done I'll give whoever $100 for the frame. Never let it be said that I would take advantage of anyone.:D
 
BEEN DONE (NUMEROUS TIMES)

I got at least three of this 'cut the barrel' test articles in older gun magazines.

I don't care; only relevant in THAT gun.

I wanna know about MY gun.

Buy a chrono and test. Then you KNOW.
 
Re: How long of a barrel does the .357 need?

Well...

A 3 1/16" SP101 gives 1,245 fps with Ga Arm's 158 grain GoldDot "Deer Stopper"

A 16.25" Marlin 1894CP gives 1,855 fps with the same load.

That's a helluva a jump.

I'd say at least 16"... probably a touch more. There is still good muzzle flash with the 16.25" barrel.

Kilgor
 
IME: Cylinder gap has the biggest effect on velocity, especially snubbies. I'm assuming we're discussing gun variables, not ammo variables here.
 
I read that a 444 marlin, which has vastly more powder in the case than a .357, needs only 18" to completely burn the powder. That's not to say that a longer barrel won't push the bullet a little faster, but you will reach a point of diminishing returns in which there is still gas in the barrel but it's not adding anything to velocity. At some point the barrel friction will reduce velocity.
 
In regards to barrel length and the burn rate for a 357....arent there to many variables to really know...fast burning vs slower burning? I know in shorter barrels faster burning powder gives more velocity..but you lose out with a longer barrel with fast burning powder. My old man reloads to make them match.......
just a thought

Shoot well
 
I would rather see the difference for the barrel gaps in a dan wesson. Set it up tight and run a cylinder through it. Open up the gap a little, and do it again.

I got lucky buying a used revolver without checking cylinder to whatever gap, I did not know it was something to consider.

I think the difference in barrels matters once you know how bad the cylinder gap is affecting velocity.

I have a ruger 101 and a 100, and they both have 3 inch or so barrels, see the 3 1/16 barrel above. Other than a little difference I attribute weight, they are pretty darn close.
 
The amount of velocity from a firearm is dependent upon....

"Expansion Ratio." :)

This is the relationship of the chamber (case minus the space the bullet takes up) to the total volume of the chamber and barrel length. It is greater for larger calibers... obviously a 45 barrel develops more volume per inch than a 22. :eek:

Now, variations such as cylinder gap, chamber mouth diameter, bore condition (some are just slicker than others) make a good deal of difference in velocity. The old arguement about if an autopistol, a revolver, or a single shot gives more velocity. I've never seen a study that could answer the question in practicality. There have been enough studies to show the cylinder gap in a revolver does not cause as much velocity loss as predicted.

And, despite much speculation to the contrary, a casual examination of loading manuals will show that heavy doses of slow powder still gives higher velocities from short barrels than fast powder. Fast powder gives more velocity per grain, but slow powders still more total velocity.

I recomend the book "Pressure Factors" from Wolfe Press.
Also, if you can find a "Powley Calculator", just using the device will show you much about the process.
 
I think there is more difference to be found from normal variations in bore diameter than from normal variations in cylinder gap.

Plus what WS2 said bout chamber etc variations.

Sam
 
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