For a .357Mag to reach full potential - how long a barrel?

R

raindog

New member
I've read that a .357 Magnum revolver with a 2" barrel is not long enough for the round to reach its full potential. I'm not sure I understand why. When the charge ignites, the bullet starts moving forward. Does this mean that it escapes the barrel before the full force of the charge pushes it?

And on that note - how long is long enough for .357 Mag? 4"? 6"?
 
Yes, pressure from the powder burn continues to push the bullet down the barrel, and the bullet leaves the barrel while still being pushed. In fact, a .357mag shot out an 18" rifle barrel gains velocity over a 6" revolver, so technically, it takes at least 18" for this cartridge to reach it's full potential. More relevant, then, is how much barrel do you need for your .357mag to do it's job.
 
You are right, it leaves the barrel before all the powder can burn. Normally, velocity in a 6" bbl will be higher than a 4" or a 2". This also applies to semi autos. There are exceptions, the gap between the face of the cylinder and the rear of the bbl can cause the velocity to be higher or lower than normal.
 
http://www.ballisticsbytheinch.com/calibers.html

Click on the 357 mag icon and look at the different velocities based on barrel length.

Most of the published data you see is from 8" test barrels with no cylinder gap. Any rifle or handgun chambering needs some barrel length for all of the powder to burn. Most will burn within a few inches, but the pressure still builds up as the bullet passes through the barrels. A 357 from an 18-20" rifle barrel will be quite a bit faster than from even an 8" barrel. A 4" barrrel is only 1/2 the test barrels length and a 2" is 1/4. You will lose serious speed from barrels that short. A 2" barrel in most loadings is 500 fps or so slower than from an 8" barrel based on the above link. Almost 1000 fps slower than from an 18" rifle barrel in some loadings.

Also some cartridges use less powder, or are more efficeint and don't need as much barrel to reach their full potental. Magnum handgun chamberings with barrels less than 4" long are about useless for my purposes. Most of the published data for semi-autos is more accurate because they are tested in barrels closer to what people actually use. One reason the 9mm killed off 357 mag in law enforcement was when folks figured out their 6 shot 357 mags with 4" barrels were only shooting around 50 fps faster than a 15 shot 9mm when using the common 124/125 gr loadings.
 
The original .357 Mag load was a 158gr bullet at 1500fps, from an 8.75" barrel; a barrel shorter than that will not allow the cartridge to reach its full potential.
 
If you look at the graph on the link:
http://www.ballisticsbytheinch.com/calibers.html

If you average the energies of all of the loads (excluding that low Blue line) at 2", it is just under 300 ft-lbf. Then compare that to the average at 4" which is just over 600 ft-lbf. So you get a bit more than a 100% increase for going with a 4" compared to a 2".

When you compare the 4" to the 6" barrel it shows an energy of just under 800 ft-lbf, you get an increase of about 30%.

When you compare the 6" to the 8" energy figure of about 900 ft-lbf; you have an increase of about 12.5%.

Guess this is why many people "settle" for a 4" or 5" barrel as "good enough".
 
Just an ideal:

I load 150 Grn LSWC with 14.5 grns of 2400 to 1328 out of my 4 in Model 28.

I run the same bullet through my Marlin '94 at a tad over 1900.

I forgot what that load does out of my 6 in Model 27 but I do know it raises heck with bowling pins.
 
Sometimes comparisons will show newer guns with shorter barrels having similar or better velocity then an older gun with a longer barrel, (Buffalo bore chart.) But generally you need a six inch barrel, at least, for complete powder burn.

For hunting I've always thought a Contender in 357 mag and a 12inch barrel is a totally different gun then revolvers with 6 & 8 inch pipes.
 
somebody's dreaming. 600 ft lbs in a 4" 357?

not happening. 500 ft lbs, yes, 600, no. Not with standard factory loads, and certainly not with anything that is even remotely like fast enough for combat repeat hits.
 
Buffalo Bore and Double Tap both offer 158 gr. rounds that reach 600 ft. lbs. in a 4" barrel. I couldn't tell you if either allows for quick follow ups...but nobody is "dreaming".
 
not happening. 500 ft lbs, yes, 600, no.
Click to expand...

Why?

It's not that difficult to get 600 ft lbs out of a 4 inch M-28. As I said I use 150 grns @1328 FPS. That's not a hot load but its 588 ft lbs. If I was to use 158s at the same velocity (doable) it would be 619 ft lbs.
 
The advantage to handloading ammunition is to match powder to barrel length, more or less.

Some powders, such as Bullseye, Winchester 231, and Hodgdon's HP-38 deliver pretty respectable velocities fired from the cylinder, no barrel.

Very fast burning powders work well with short barrels, while the slow burning powders work their best with barrels running in excess of 4".

Bob Wright
 
for medium game, my 6 1/2" barrel Blackhawk .357 get almost 1500fps with Federal Eagle, fair recoil. No where that much with my 2" snub and recoil is awful.
 
the link posted above is not from a revolver. The revolver info is under the cylinder gap section.

With a cylinder gap of .006 you can see the velocity dies down much faster due to the escaping gasses. You gain about 200 fps from 2" to 6" barrel, and about the same from 6" to 18". the ratio of barrel length to velocity narrows considerably because the longer the bullet is in the barrel the more gasses can escape through the cylinder gap. You don't get that big increase like would from a Thomson or Marlin.

Cylinder Gap Test
 
the link posted above is not from a revolver
Click to expand...
I am assuming that you are referring to the Ballistics by the inch quite a bit up the page; not the Buffalo Bore link directly above your post.

I can assure you that the numbers which I posted are still on my chronograph.
 
As a general rule of thumb, for revolvers, you will loose 50 FPS for every inch the barrel is shortened. Therefore if a 1,000 FPS is still the Minimum standard for bullet expansion you would want a round that is traveling at least 1,200 FPS from a 6" barrel.
 
The wide variation of .357 Magnum loads and the effect of cylinder gap kind of makes it impossible to state definitively.

I think the velocity gain from adding barrel length peaks for most loads around 4" to 6". That is, you gain a lot of velocity from barrels up to that length, but after that length the gain is much smaller, to the point that if you have a 20" rifle, you're probably not gaining more than 5 fps or so and may actually be losing velocity over a 16" or 18" carbine.

Other loads are optimized for short-barrel snubnose revolvers.

My personal preference is 3", which is a compromise between the full effectiveness of 4" barrels and the size of the 2", while retaining most of the velocity gains from the longer barrel and minimizing the muzzle flash and flip of the snubnose.
 
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