help me understand: .38slp vs .357 mag

c&rdaze · Jul 27, 2017

okay, I'm not the most knowledgable reloader. I recently came into the 'ownership' of a S&W 19-3 .357. If you look at some of my recent threads, you'll see that I have had some questions. Here we go again.

I'm trying to reload some .38spl to +p for use in the .357. My chrono doesn't make sense to me. Bottom line the .357 shoots slower than the .38spl by about 200 ft/sec with commercial Rem and my handloads. Is this normal because of the shorter length between the two loadings. and the 'jump' to the threads.

Details: Rem commercial 158 gr lead RN; Victory 819ft/sec; .357 682ft/sec.
Handloads: 5.0gr Unique 158 plated HP; Victory 765ft/sec; .357 560ft/sec.

iH8DemLibz · Jul 27, 2017

By threads, do you mean rifling?

If so, I would think you'd bleed energy the farther from the rifling you are.

Takes longer to seal the chamber/bore.

c&rdaze · Jul 27, 2017

Yes, the lands and grooves

Biggfoot44 · Jul 27, 2017

It's not a .38spl gun vs .357 gun thing . ( Ok 95% not a .38 vs .357 thing.) It's an individual gun vs individual gun thing . Your Victory gives velocities well within expected . Your M19-3 is " Slow " . Stupid question, what is bbl length on M19-3 ? 4In or 2.5in ?

Velocities with specific guns, even same make and model are effected by multiple factors, often they somewhat cancel out each other, but sometimes will stack all in the right/ wrong .

Chamber diameter, headspace, throat dia, throat surface, forcing cone shape and surface, exact internal bbl dimentions. And bbl cylinder gap . What's your b/c on the M19 ?

noylj · Jul 27, 2017

Describe what EXACTLY you are doing, as it really isn't clear to me.
If you use the same powder charge in a .38 spl and .357 Mag case, the .38 Spl will almost always produce higher velocity due to higher pressure.
If you compare a .38 spl in a .357 Mag revolver and the same load in a .38 Spl, you might get higher velocity from the .357 Mag revolver due to the longer free bore.
If you compare your gun with the velocity in a manual, you'll often be disappointed. The manual might be using a longer barrel or a minimum chambered barrel in a Universal Receiver; but even with the same barrel length, two barrels don't shoot the exact same velocity.

c&rdaze · Jul 27, 2017

Barrel length: .357. 4" ; Victory. 5" ( converted with .38spl cyl.)

c&rdaze · Jul 27, 2017

Same charge. Just surprised by the different ft/sec..

Magnumite · Jul 28, 2017

I would say the Smith is 'slow'. Going from my 357 revolvers to equal length 38 Special revolvers typically produced similar but not identical velocities. Is the barrel breech face and forcing cone eroded on the 357?

Jmorrismetal · Jul 28, 2017

c&rdaze said:
Same charge. Just surprised by the different ft/sec..

Put them at the same OAL and see what they do.

At that point there will be no difference in internal volume. A 38 spl at a "normal" seating depth will have a shorter OAL than a 357 mag, because the case is shorter, thus smaller internal volume. That in turn effects pressure.

I don't have any numbers for either of them but Speer did some tests with 9mm and with one combination tested, seating a bullet .030" deeper raised the pressure from 28,000 cup to 62,000 cup.

If you are seating a 38/357 bullet to the same depth in respect to the case mouth you are changing internal volume by .135" and yes that will make a difference.

ken792 · Jul 28, 2017

noylj said:
If you use the same powder charge in a .38 spl and .357 Mag case, the .38 Spl will almost always produce higher velocity due to higher pressure.

I thought it ends up with lower pressure and lower velocity since the .38 has more to jump before it hits rifling in a .357 gun?

yellowfin · Jul 28, 2017

ken792 said:
I thought it ends up with lower pressure and lower velocity since the .38 has more to jump before it hits rifling in a .357 gun?

The amount of velocity difference due to jump is nowhere near as significant as that caused by difference in case volume.

Biggfoot44 · Jul 28, 2017

Is the OP loading in both .38spl and .357 cases respectively? Or the same batch of loads, in .38spl cases , fired in each gun ? I was *assuming-* the latter.

In theory, with everything else equal, a .38spl ctg fired in .357chamber will have lower velocities than if fired in .38spl chamber . But if you could isolate it, it would be on the order of 10fps . Much less than usual gun to gun variations.

BuildnBurn · Jul 30, 2017

How far away is your chronograph? sometimes having it too close to the muzzle blast gives hinky velocity results.

Blacksmith101 · Jul 30, 2017

c&rdaze said:
okay, I'm not the most knowledgable reloader. I recently came into the 'ownership' of a S&W 19-3 .357. If you look at some of my recent threads, you'll see that I have had some questions. Here we go again.

I'm trying to reload some .38spl to +p for use in the .357. My chrono doesn't make sense to me. Bottom line the .357 shoots slower than the .38spl by about 200 ft/sec with commercial Rem and my handloads. Is this normal because of the shorter length between the two loadings. and the 'jump' to the threads.

Details:
Rem commercial (powder?) 158 gr lead RN; Victory 819ft/sec; .357 682ft/sec.
Handloads: 5.0gr Unique 158 plated HP; Victory 765ft/sec; .357 560ft/sec.

Apples to Oranges.
In addition to the other differences noted in the above posts.

Try some ballistics gel and see if you are happy with the results of the penetration and expansion. If the accuracy, recoil, and flash are also acceptable don't worry about what the chrony says.

Biggfoot44 · Jul 30, 2017

Was that R-P factory control load a std vel or a +P ?

As noted above the lead vs Plated is a significant variable in velocity. In an apple vs apple comparison using a 158gr commercial cast bullet of the Magma Engeneering style ( most mass produced commercial cast bullets ) , 5.0gr Unique will be reasonably close in vel to typical 158gr lead +P factory loads.

c&rdaze · Aug 16, 2017

Thanks for all the thoughts. The R-P factory load was not listed as +p, had assumed it was std loadings. Before chrono and reloading, used this in my .38spls. I got the chrono because my first handloads 'felt' hotter that the R-P loads, even as they were loaded on the lighter side of my Lyman book.

Still don't understand why the same .38spl ammo shows such a different in velocity when fired from 38spl vs. .357. BTW, .357 loaded cases come in right at specs per Lymans book.

caederus · Aug 18, 2017

c&rdaze said:
Barrel length: .357. 4" ; Victory. 5" ( converted with .38spl cyl.)

c&rdaze said:
Still don't understand why the same .38spl ammo shows such a different in velocity when fired from 38spl vs. .357. BTW, .357 loaded cases come in right at specs per Lymans book.

Barrel length will have a significant impact on velocity, due to the increased time that the pressure is put into accelerating the bullet. Up to a point the longer the barrel the higher the velocity. So a barrel that is 25% longer 5" vs 4" will produce a higher velocity, but not 25%.

Blacksmith101 · Aug 18, 2017

caederus said:
Barrel length will have a significant impact on velocity, due to the increased time that the pressure is put into accelerating the bullet. Up to a point the longer the barrel the higher the velocity. So a barrel that is 25% longer 5" vs 4" will produce a higher velocity, but not 25%.

Cylinder gap differences, chamber differences, forcing cone fouling, chamber alignment, bore and rifling dimensions, etc. lots of variables between two revolvers.

caederus · Aug 19, 2017

Blacksmith101 said:
Cylinder gap differences, chamber differences, forcing cone fouling, chamber alignment, bore and rifling dimensions, etc. lots of variables between two revolvers.

Between the two revolvers specified the one difference that will have the largest impact on velocity is the barrel length.

Mike · Aug 19, 2017

caederus said:
Between the two revolvers specified the one difference that will have the largest impact on velocity is the barrel length.

This site has results for several caliber and barrel lengths

.357 Mag Results in fps
http://www.ballisticsbytheinch.com/357mag.html

For example

18" 1718
5" 1377
2" 928

help me understand: .38slp vs .357 mag

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