I’ve wondered about this. My S&W revolver uses 38 sp. My Ruger LCP uses 380 ammo. Here’s the difference. You can’t fit a 38 sp into a 380 clip. 
But is it ok to use 380 in a 38 sp revolver? It should fit in the cylinder. How about a 357?
I know the 380 doesn’t have the same stopping power. But in an emergency it’s better than nothing.
It might fit, but it’s not a good idea.
Lots of little differences, of course. The .380ACP round is actually a tad smaller in diameter than the .38sp. That’s one reason the .38 rounds don’t fit into the clip.
They’re designed for entirely different applications, too. The .380ACP for semi-autos (it’s rimless) and .38 for revolvers (rimmed). Unless it’s a real emergency, I wouldn’t even try it.
You can (though it’s not recommended) fire .38 out of a .357, but the reverse is not true. It’s generally a bad idea to try firing .357 rounds out of a .38 special.
.38 special headspaces on the cartridge rim. .380 headspaces on the case mouth. The .38 special cartridge (not the bullet) is .379 inch with a 1.55 inch OAL. The .380 cartridge diameter is .373 inch witha .984 inch OAL.
I expect your .380 cartridges would drop down too far into the cylinder chambers for the firing pin to hit the primers. You’d likely end up poking them back out with a pencil. If you did manage to get one to go off, the case would split and the undersized bullet would not properly engage the rifling. You’d have very poor velocity and very poor accuracy.
I didn’t think about the rim on the .38sp. Glad I asked. Thanks!
Absolutely not. The .38 S&W Special is a rimmed cartridge, and the .380 is rimless. Not even if you used moon clips - which don’t exist for .380 IIRC - there would still be some play or wobble.
A .38 Special is .357 inches in diameter. A .380 is .354 inches. You may not think that’s much difference, but it’s miles in machining world.
In a dire, burglar in the other room emergency, where you only had the .38 gun and .380 ammo, you could try, but the results would be questionable. Maybe the bullet lines up some and goes down the barrel, maybe it catches and blows out the front of the cylinder. I’d have to be pretty desperate to try it.
A .357 bullet is, oddly enough, .357 inches in diameter, and so matches the .38 Special.
You can shoot .38 Special in a .357 Magnum gun, but not the other way around. The .357 cartridge is a bit longer and will not fit in a .38 gun.
There is also the .357 Sig and .357 GAP, neither of which are compatible with the others.
Only in a bizarre set of circumstances should you find yourself with this gun and that ammo.
Please prepare more thoroughly. 
What do you mean it is not recommended?
TLDR version: Don’t do it. Stop thinking about it.
Longer version, if you want to know why:
Disclaimer: The information below is theoretical only. It is a fundamental safety rule to only use ammunition for which the gun was designed. Using the wrong ammunition is a good way to ruin a gun, get injured, and possibly die. There are a small number of guns that are designed to handle multiple chamberings and the manufacturer will indicate when these are safe. To my knowledge these are:
.410 shotgun shells may be used in a few .45 colt revolvers and derringers designed to allow this. MOST .45 colt revolvers only handle .45 colt however.
.45 colt rounds may be safely used in .434 Cassul guns.
.44 special rounds (rare) may be used in .44 magnum guns.
.38 special rounds may be used in .357 magnum guns.
In the last three cases, the more powerful round is a “magnumized” version of the less powerful one. The cases of the higher powered round are always a bit longer so that they will not fit in guns not designed to handle them. Using the lower powered rounds may not be without problems, but it is not dangerous.
In addition there are a few guns with interchangeable cylinders are barrels that allow additional calibers to be used with no issues. .22 LR and .22 WRM and .45LC ancd .45ACP are examples that Ruger currently produces revolvers with multiple cylinders.
First off, a .380 (or 9mm) bullet is a couple thou smaller than a .38 (.355 vs .357) it will not cause excessive pressure, but accuracy may be poor. The .380 bullet might barely engage the rifling, and perhaps not at all if it is very shallow, and it may not seal well, regardless. I believe at least one manufacturer (S&W or Taurus?? heck, maybe it was Ruger?) DID offer a revolver with 9mm and .38spl interchangeable cylinders, so apparently the bullet diameter is close enough for jazz?
Next, as has been mentioned, There is no rim on a 380 round, thus nothing to hold it in the proper position for the firing pin. If you pointed the revolver upward, there might be enough inertia from the round to allow the percussion of the firing pin to fire it. Then the REAL trouble starts:
The firing pin will drive the case forward before the powder really gets burning. Eventually the powder lights up and the pressure builds, forcing the walls of the case against the walls of the chamber. This is what seals the breech of all cartridge based arms, even shotguns where lower pressures allow paper or plastic hulls to do the job. With the walls of the case press tightly to the chamber walls, the rear of the case (the “head”) is driven rearward until stopped by whatever closes the rear of the chamber…bolt, slide, revolver frame, falling or rolling block, etc. I’ll just call it the breech block. This stretches the case in the area just forward of the head. If the distance from the rear of the case to the breech block (“headspace”) is too much, then the case will tear (“rupture”) and high pressure gasses will be vented rearward. This is bad, but occasionally happens, so firearms are usually built to protect the shooter from the problem. Many guns protect right-handed shooters, but expose left-handed shooters, and many of the few left-handed guns do the opposite. A true ambidextrous firearm must vent gas from a ruptured case or primer in a way that protects both righties and lefties.
Note that cases get stretched slightly even with correct headspace, as there must be a little headspace to allow a maximum tolerance length round to be fired without jamming. If a case is reloaded many times, it will eventually rupture due to this stretching. This is something experienced reloaders are aware of and alert for.
Anyway, the point is that the head space must not be excessive, or you can expect the case to rupture, and if you manage to get a .38 to fire a .380 round, it is very likely, virtually certain in fact, that the case will rupture, venting hot gas, possibly injuring the shooter, the gun, and almost certainly jamming it to the point that extensive disassembly and inspection will be required to return it to service. It might cut and/or burn your hand, might blind you, but you will most likely live.
Revolvers typically use rimmed cases to control headspace. The thickness of the rim and the fit of the cylinder to the frame determine the headspace. This is what allows some revolvers to fire different length cases. It also simplifies the ejector for double action revolvers.
Rimmed cases often cause feeding trouble in stacked magazines. So rimless cases were a solution. There is an extractor groove, but the “rim” behind the groove does not extend beyond the body of the case. 9mm and .45 ACP were initially intended to approximate the ballistics of .38 spl and .45 colt in a rimless case, with smokeless powder loads.
Since rimless cases lack a rim to control headspace, some other solution is required. Bottlenecked cases (mostly used in rifles) headspace from the shoulder where the case diameter transitions. Straight walled cases (like 9mm, 380, .45 ACP) headspace off the case mouth.
The few revolvers that work with rimless ammunition have cylinders with chambers that provide a precise step for the case mouth to control headspace. They also use either half or full-moon clips to allow the ejector to work. The clips are not required for headspacing or safe operation. In a pinch the revolver may be used without the clips, and cases ejected one-at-a-time using a pencil or similar. Revolvers that fire rimless ammo are the exception, but not exactly rare. Many S&W .45 ACP revolvers were issued during and for a while after WW1, because production of the 1911 automatic was not sufficient to supply demand. S&W revolvers helped fill that gap, while still using the same ammo.
I wouldn’t expect anything to “blow out the front of the cylinder” no matter what else happens if you tried to fire the .380 in .38 special revolver. The .380 is a low pressure round. The fit is loose between the .355 bullet and the revolver’s cylinder and barrel, but not loose enough to let the bullet turn sideways and “hang up”
The now out-of-production Medusa revolver was able to fire a bunch of different pistol cartridges, both rimmed and rimless, because of the rather clever extractor mechanism. It would fire both .380 and .38 special. The only real issue with something like this is making sure the cartridge headspaces on something in such a way that the firing pin can hit the primer. Hence, the clever extractor.
Although, as far as I know, nobody is making Medusa revolvers any more, there is a Medusa conversion cylinder still sold that will let you convert your revolver into a multi-cartridge platform. They’re pretty pricey. Last time I saw them advertised they were about $800 a pop and required gunsmith installation.
Using the short rounds in the magnum revolver forms deposits at the front of the chamber. It may even etch/erode the metal a bit. This can cause the full-length cases to stick in the chambers, and in extreme cases, not want to go in.
In most cases, such can be removed with aggressive cleaning, but this in itself can accelerate wear on the gun.
Or it can be prevented entirely with non-aggressive, normal cleaning after each use. I just can’t imagine this actually being an issue, and there are far more benefits to shooting .38 out of a 357. It is recommended far more often than not. Cost alone is reason enough. Just clean the thing when you’re done, which is good advice in general anyway.
Interesting that the 38sp ammo I have (Remington UMC Target) is 130 grain 950 fps. The 380acp (also Remington UMC Target) is 88 grain 955 fps. Quite a bit smaller projectile but the same velocity.
Yes, they do. THIS revolver uses them.
Agreed, that is what I do. I was responding to why it is “not recommended” by some, and so presented those arguments. Falling into the media trap of reporting both sides of the issue while failing to note that one side is mostly hot air I guess.
Nuh uh. It uses “Taurus Stellar Clips”.
Anyway, it doesn’t count, because it’s new and I didn’t know about it! 
Like others have said, shooting standard loads in a magnum revolver , ie 38 sp. in a .357 is fine but needs to be cleaned well, and even thou Klevbo miss quoted with the Casull, it’s a .454 Casull not a .434 but some firearm manufactures like S&W in the .460, tarus in the raging (boy) Calf and Ruger will ok .45 Colt in the …454Casull, however Freedom Arms states to not do this and we have a .45Colt cylinder as a conversion. the gun is just to tight in tollerences I believe.
There is a revolver that was designed to shoot any 9mm, 38,357 cartridge on the market in the same gun/same cylinder. 25 different loads are suppose to be able to be loaded and fired in this,
Medusa model 47 revolver.
:http://www.kitsune.addr.com/Firearms/Revolvers/Medusa_Model_47.htm
All soda in Texas is called Coke, y’know!
Any way, I’ve never been much of a revolver guy. I did have to carry one for almost 10 years before they let us transition to pistols.
But I’ve contemplated getting a hammer-less double-action-only revolver for off-duty winter carry. If I had to shoot through the coat pocket I was carrying in the slide of an semi-auto might get jammed up in material. I currently carry a Glock 19 on duty and a Glock 26 off duty (both 9mm) so for revolver I’m thinking the Taurus M-905 in 9mm.
I wish THIS came in spurless DAO as a snubby. It allegedly takes both 9mm AND .380 WITHOUT the use of Moonclips!
I’ve always got my 442 or 340with Crimson Trace grips on me.
Now, if you really want a man’s revolver, the S&W 500 is just the ticket. You only need one round. You’ll either shoot them, blind them, burn them, or deafen them, probably all at once.
Agreed with everything else in the thread, except this. And, I know this is GQ, but do you have a cite? I was always told that with a .357mag you could shoot .38 special, .38 special +P, +p+, or .357 mag…shooter’s choice…
Why is it not recommended? I know of no safety issues doing it. If you’re talking about comparative stopping power between the .38 round and the .357, then I would agree that the .357 is better.
When I first got into law enforcement in 1982 almost every department I knew of carried .357 magnum revolvers but issued .38 Special ammo. Back then my agency was one of the few to load the full .357 magnum rounds in 158 grain hollow point.
City of Milwaukee at one point was issuing .38 wadcutters for gawds sake!
There is no good reason to avoid firing .38Spl in a .357Mag revolver. The only issue could be buildup on the barrel end of the chambers due to the slightly shorter length of .38Spl that prevents .357Mag rounds from seating fully. This only occurs when .38Spl is fired in large quantity without cleaning the weapon, so it’s a non-issue unless the shooter is very lazy.
