9MM Federal Rimmed vs. .38 S&W

T

Tom-Fairfax

New member
I hope this is the right forum because I have one final question about whether the 9MM Federal Rimmed cartridge is interchangeable with the .38 S&W. I'm asking because the 9MM Federal Rimmed is out of production. Since I own two Charter Arms Pit Bull revolvers that are chambered for 9MM Federal Rimmed, I need to see if the .38 S&W will substitute as ammunition. The specs for both cartridges are as follows:

9 mm Federal (9x19 mm)
Type: Rimmed
Bullet Diameter .355 in (9.0 mm)
Case length: . .754 in (19.2 mm)
Rim Diameter: .435
Neck Diameter: .382
Base Diameter: .386
Cartridge length: 1.163 in (29.5 mm)

.38 S&W
Type: Rimmed
Bullet Diameter: .359 in (9.1 mm)
Case length: .780 in. (19.8 mm)
Rim Diameter: .433
Neck Diameter: .386
Base Diameter: .386
Cartridge length: 1.200 in (30.5 mm)

The cartridges look similar enough so that I wonder if I can use the .38 SW straight out of the box. The Pit Bull cylinder is deep enough to chamber it. However, all of the reloading information I've read suggests that the proper way to approach this is to cut the .38 S&W case length (.780) down to the length of the 9MM Federal case (.754). Since I clearly don't know anything about this issue, I'd appreciate your assistance in sorting it out. Thanks.
 
I remember the 9mm federal but had no idea it was so close to the 38 S&W in all dimensions. Sounds as if it would work fine. If it were me I would try a sized but not crimped case (I'm assuming you already have dies) in the cylinder and if it fit I wouldn't even trim them.
 
Tom,

Your .38 S&W dimension are off a little. The case length is 0.775" with a -0.020" tolerance, so much commercial brass will be made in the middle of that range at about 0.765", though Starline says theirs runs 0.767"-0.773", so they're holding tighter and averaging 0.770". It's close enough that it may chamber for you, but sizing in a 9mm sizing die (which will grow their length a little), then applying a Lee trimmer adds a safety margin. The crimp in the typical lead bullet is more significant than with a jacketed bullet, so they could chamber with the crimp inside the mouth of the throat at firing, raising pressure.

.38 S&W barrel groove diameter is 03595" minimum with a +0.004" tolerance. In modern guns .360" will be typical and swaged lead bullets should tend to be 0.3605"-.361". So, the bullets will be a little bigger than you thought. Most revolvers like like lead 0.001"-0.002" over groove diameter, so 0.356"-.0357 in your gun if your bore has the nominal 0.355" groove diameter. But you need to slug the bore and chambers to be sure of what you've got. A lead bullet .3610" will probably shoot through if it chambers, but accuracy would not be expected to be great and pressure will be higher than in a gun the right size for the cartridge.

The .38 S&W design peak pressure is half that of 9mm, so you may find the cases aren't as thick at the head and may not be up to the added pressure a 9mm case is. That may or may not be an issue in the revolver, as it surrounds a case more completely than some semi-autos do. Unfortunately, the only way I know how to find out is to work loads up carefully and make sure you don't start seeing head expansion or loose primer pockets or sticky extraction. They aren't perfect pressure indicators, but should be heeded if they show up, and the charge weight dropped 5% right away if they do. Otherwise, you can also just use the .38 S&W brass for light target loads.

The few thousandths thinner rim of the .38 S&W may cause no problem, but if ignition force and firing pin protrusion are marginal in your gun, it may make ignition less reliable. Generally, I find Federal primers are more easily ignited than most in that situation, and using them can help if a problem comes up.
 
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~10 years ago when I was learning handloading..
In 38 S&W with an Iver Johnson second model third variation hammerless break top manufactured in 1898*, I was working my up from:
6.2 gr Blue Dot 158 gr JHP 1.24" 25kpsi QL
to:
9.4 gr Blue Dot 158 gr JHP 1.24" 109kpsi QL

But I never made it.
I had to stop at:
7.8 gr Blue Dot 158 gr JHP 1.24" 52kpsi QL

I had to stop there, as the eye of the latch stretched stretched into an oblong shape making the break top have 0.020" of looseness.

I told my father that pressure stretched the latch, but he yelled at me that recoil on the barrel mass and bullet friction in the bore stretched the latch.

My father got gun patents like this:
http://www.freepatentsonline.com/2857815.pdf
And yelled in people's faces.

I could not argue. I had to switch to softer bullets.

*I just now had to figure that out with a copy of the book "Iver Johnson" by Goforth
 

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SPECIFICALLY, the 9MM FEDERAL ammunition was dropped from production when it was discovered that it would drop right in old 38S&W chambered revolvers and turn them into scrap in a heartbeat.
I still kept all of my supply of 9MM FEDERAL ammunition...just in case.
And so it goes...
 
Well, once I discovered it, I managed to get hold of some and it's going to be used in a Martini Cadet 9mm Rimmed that I'm having built. It ought to be ONE FUN GUN!:D
 
I had heard that the reason the 9MM Rimmed was created was for LEO who wanted a back up revolver chambered in 9MM to equate to their semi-auto issued sidearm. When LEO started dropping the 9MM in favor of the .40 cal, the whole Charter Arms/Federal project went south.
 
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