I'm wanting to do this but I have a few questions first.

By doing this there will be a larger gap between the bullet's base and the powder. Is this ok?

That's perfectly OK. For reference, I just stepped away from my bench where I'm loading 6 grains of HP-38 in .357 mag cases. It might fill half the case. It's been my go to load for years and I may step outside to my range and shoot box before it even gets to my ammo cabinet LOL. If it'll chamber a .357 case, I'd use light .357 load data. The one I mention above is quite mild. A really nice range load.

Should be fine,just make sure any bunny fart loads clear the barrel

I was thinking of loading them to +P 38 special loads.

If you want the same velocity as the load develops in the .38 Spl. case you have to increase charge weight by approximately 15% to maintain the same loading density.

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Gunsmithing since 1961

I think it was Skeeter Skelton, that used .357 loads in .38 Cases.

He loaded LEAD semi-wadcutters/ H.P.'s to the first grease groove, instead of the crimp groove, to obtain a similar powder space.

I am NOT recommending you do this.

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NRA Instructor

Even in 38sp, there is always an airspace with most powders. With identical charge was, pressures & vel will be slightly lower in the mag case. So you will have to bump charge wt, but there is no real % increase, it's powder specific.

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NRA Cert. Inst. IDPA CSO

The .38 was developed in the black powder era and was switched to smokeless. The excess air space is there because of the less volume of powder is needed. The .357 was developed later by taking advantage of the potential of the .38 with smokeless powder. The cartridges are IDENTICAL except for that tiny extra length that is only there to prevent putting a .357 cartridge in a .38 gun. The 'excess' volume is of no consequence. Most of the powders that barely cover the bottom of the case, like Bullseye or Titegroup are very easy to light with a standard primer. Slow, magnum powders like HS-6 and H110/W296 are harder to light, but fill the case more, so the flame can't miss the powder charge. But a magnum primer does insure good light off and a better burn.

PS: The versatility of the .357 is such that you can charge them with the light target loads of the .38 all the way to full full magnum loads. If you stay with published loads you won't stick a bullet in the barrel.

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"He was kinda funny lookin'"

6 grains of HP38 or Win.231 takes this load well past the 38 special range in power and from what I understand, would effectively constitute a double charge in a 38 spl case!
Jim

Top end 38+p loads in 357 brass should be fine, but the starting loads could be too light, especially with jacketed or plated bullets.
I always use data for 357 brass when I use it. Plenty of light 357 data out there. Then you always have a safe minimum and some idea of the speed.

Skeeters load in a 38spl case used the Lyman 358156 cast bullet designed by Ray Thompson . It has 2 crimp grooves . If loaded in a 38spl case, to get 357 performance you crimp in the lower crimp groove for the extra case capacity . If loaded in 357 mag cases , crimp in the upper crimp groove . This is probably the most used cast design on my bench for 357 magnum loads in 357 cases . Yrs ago I did like skeeter and used 38spl cases because I didn't have many 357 mag cases . Today i have plenty and don't load 357 in 38spl cases .

I shoot light target loads of 148 gr HBWC out of .357 cases in my .357 686 with a 6" barrel. The 2.8 grains of Bullseye or some equivalent works fine. There ain't no way a standard .38 load would be 'too light' in a .357. Again, that extra tad of length is only there to keep from chambering a .357 in a .38 special gun. The increase in volume is miniscule compared to the space inside the cartridge.

The same works for the .44 special and the .44 magnum, which makes both of these guns very versatile.

PS: I also shoot jacketed bullets with .38 loadings out of my .357 with no problem. If you go below minimum loads for .38 special, you are risking sticking a bullet in the barrel.

PPS: This only applies to the cartridges mentioned here. The .357 and the .44.

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"He was kinda funny lookin'"

No, 6 grs of 231 in a 38 spl case would be a bit too much but
nowhere near a double charge. I have seen 5.4 grs listed in
one of my manuals with a 158 gr JHP as being within +P
limits.
If 38 spl velocities are wanted in 357 brass with 231 just add
about .5 grs. The exact amount isn't critical but it will take
just a little more powder.

re: "How do you load a 38 special charge in a 357 magnum brass?"

I gave up on that concern decades ago.The constant confusion of which load/which gun etc finally made me develop an answer that works well for *me* YMMV.

I don't load "38 special charges in a 357 magnum case".Because I do have some old guns that only take '38 special', I experimented with a wide range of recipes, and load my 38 cases within the range of low to moderate to hot 38 special specs.I load my 357 magnum loads all in the 357 spec ranges as published by the mfg of the powder being used. Never an issue, as I get better accuracy etc with both.

Trying to factor in where a wide range of variables already affect ballistic performance, on top of my own geezer-variables, I like my POI to remain as constant as possible.I have not found it necessary to use 'magnum' primers in any of the recipes I've developed over the last 25 years.

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Dum vivimus Vivamas

I load 38spl charges in 38 cases, and load 357mag charges in 357mag cases.

If you want to make a lighter 357mag load, that is fine. I wouldn't be trying to duplicate 38spl loads in mag brass though. Just me.

If anyone else likes to do it, then more power to them. I prefer not to.

I'd like to do it so in my .357s when I go to shoot the magnums I don't have to worry about the shorter burn rings of the .38 special brass.

I have loaded .44 mag cases only, for decades. I don't for .357 since I have a couple baby Chiefs that use .38 only. I do use the ring for the dies that change .38 to .357 height w/o resetting all the dies. Seating die gets adjusted for bullet change.
To keep easy visual track of my .44's I load lead bullets to special spec, and JHP to mag spec.

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"from my cold dead hands" C.H.

A chrono is your friend...

Why is that a concern?

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Wisdom comes thru fear . . .

Probably because he doesn't want to clean out the carbon ring (which is no big deal to do) and then a 357 case will not slide in there easy.

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Still Running Against the Wind

If you don't have a .38 special, why have more brass to sort.

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"from my cold dead hands" C.H.

But I do have a .38 special only revolver as well.

I have loaded 38spec+p loads in .357 cases without any problems. Not much different though than just loading minimum .357 loads as far as recoil that I could tell. Safe experimenting is part of the fun in reloading, key word here is safe.

"A chrono is your friend... "

Absolutely. Assuming you have some desired MV in mind, just make up some loads using any fast to medium powder (say in the Bullseye to Unique range) in a series of increasing propellant charge weights (say, 0.2 grain increments) and shoot them to see what average MV you get until you reach the desired MV. Fire at least 10 shots each. Reloading manual MV information is essentially worthless for revolvers anyway. I've discussed that at length previously, so I won't go there again.

38 brass is cheap and plentiful. Not so for 357 brass....at least not around here.

Ever hear of a thing called a brush ?

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Grumpy Old Man With a Gun

If you use .357 cases, you don't have to brush at all.

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"He was kinda funny lookin'"

I started loading 38 Specials in 1969 and .357 Magnums in 1980 and I have used 38 level loads in 357 brass many times since. The difference is the 38 loads listed in your manual will be higher than you actually get in 357 brass due to larger capacity. I have loaded cast and jacketed bullets from 125 gr. to 160 gr. and have not stuck a bullet in a barrel yet, and some loads were just starting .38 Special loads...

If you clean your guns regularly, soon after each range session, you don't have to worry about the dreaded "crud ring", brush or no brush...

I clean my guns after each session, but I always start with .38 shooting and 'graduate' to .357 about 2/3 of the way through the session. Then I can't chamber my .357s so I can make a choice either to brush out the cylinders or load .38 in .357 cases . It's not a matter of good firearms hygiene This is only when I'm shooting in my 686. The snub 38s get normal .38 fare.

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"He was kinda funny lookin'"

I also choose to use mag cases for all my high use mellow target loads, for the very same reason RW does. I shoot a heck of alot more moderate loads compared to the true magnum level stuff. Heck the cases nearly last forever when used for target loads and they don't roll away and hide like 45/40/9's!
Have plenty of spcl cases on hand to use if desired, but I just don't.

I have been following this thread, and while I do understand what the OP is trying to accomplish, I did dissect and weigh a few .38 special cases and .357 magnum cases. while there was a slight difference in weight of the .357 cases, and thickness of the brass sidewalls, they all looked up to the task of .357 magnum loads. When I did the same to the various .38 special cases, I found a big weight difference in the cases, and there was a big variance in the thickness of the case side walls. Some felt very flimsy. I found my older Winchester and Federal .38 special cases seemed much more robust than some of the other lesser brand cases I examined. Now while I feel the stronger cases would probably withstand some +P+ loads and maybe beyond, I feel that some I tested probably would not. I would suggest if you wanted to try some of those higher loads in .38 special size cases, I would trim down your .357 magnum cases and load them to the hotter specs. At least they would say .357 on them and I think be stronger cases.

My 686 does the exact same thing.

speaking of 'stiff brass', last summer I dug out an ancient stash of the nickled +38 special+ brass I hadn't used since about 1984 or so...

forgotten in an unopened box, there's a couple hundred of these old things....they loaded up fine but the rims were considerably stouter than my usual brass brass 38 Specials.

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Dum vivimus Vivamas

There is no reason not to load .38 Special pressures in a .357 Magnum case. There is little chance of causing a squib load while doing so as long as you use published data. There is also no reason to go up to .38 Special +P pressures either. The magnum case is only .125" longer than the .38 Special case. If you are not sure look at the .357 Magnum load data on the Hodgdon site for a 158gr cast lead bullet and HS-6 and compare it to the .38 Special data.

My suggestion is, use the max .38 Special charge weight for your bullet in the .357 Magnum brass with the same bullet and you will be perfectly fine.

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Freedom is never free!!
SWCA #3437

Whazzat? something NEW?
Also; I find the same thing as gregintenn; that 357 brass is scarce. My daughter suggested Amazon! (No surprise there! I think they have a plaque in her name somewhere at corporate headquarters)

YES! Starline 357 brass, and at reasonable prices/100s. Ordered enough to see me through the Zombie Apocalypse!

Addressing the original question; yes .38 Spl loads can be used successfully in 357 brass, provided you don't go too low, trying to see how low you can go! Don't ask how I know this! My personal best so far, is no lower than 3.2 gr. Unique! YMMV!
A little boy at the range asked his mom "Why is that man beating his gun?"

I shot 5.5 gr. Unique (A +P .38 load, according to a couple of my manuals.) behind the 150 gr RCBS SWC in IPSC competition for years! Chronoed 860 fps from a 4" Really nice load. But, in the True Spirit of Never Leaving Well Enough Alone, (The wife claims, but I'm sure I don't know what she is talking about!) I have gone really radical, and raised the everyday charge to 6.ogr. with 150-158 gr. boolits. Life on the edge!

My Hornady manual instructs those of us shooting full wadcutters in 357s (probably the swaged Hornady kind that are somewhat softer) to use their .38 Special loading data. They also list a max of 5 gr. Unique with their swaged SWC & HP Wadcutters, and that is a .38 Special load, which some will term "mouse fart".

If you watch on gunbroker , there are guys there selling once fired brass . Even though sometimes it isn't listed what you are wanting doesn't mean they don't have it in stock . Drop them an email .
You can always ask here on this forum for once fired 357 brass . I have fired many many rounds using " once fired " brass . Even bought a huge bag of " once fired " brass for my 357sig . It was range fodder from the Tx DPS qualifications . It has worked perfectly in my Sig P320 and it was much much cheaper than buying brand new . It was tumble cleaned before shipment . But , to each his own . Good Luck

I'm wanting to load some 38 loads in 357 as well. Anyone use Bullesye? Looking at 5 to 6 grains with a 110 XTP.
Actually found a load in Lyman's book.