I was given a bunch of 38 special brass, 158 XTP bullets and Unique powder. I have a 357 mag and want to load some heavy 38 special rounds to shoot from my 357. Has anybody had experience with this? Max load for 38 special and 158 XTP is I believe 5.2 grains of Unique in Hornady's manual.

.38 Spl shells can be shot in .357 mag but they are still .38 Spls. Pressure is determined by the volume of space that is available for your powder to burn in. The initial high pressure spike occurs before the bullet leaves the case. Too hot a load in a smaller .38 Spl case could create a pressure spike greater than the strength that a .357 mag cylinder can hold.

.38 Spl shells make great low recoil shooting from .357 mag revolvers. If you want the power of a .357 mag, load .357 mag cases.

Well said.

You can load 38 brass to +P loads in your manual. After that, your kinda on your own.

The brass is the determining factory of how much pressure can be withstood.

if you are going to load 38 spl. on the hot side you better be shooting them out of a 357 mag. most 38 spl. hand guns arent made to shoot hot loads. better to be safe than sorry.

I'd suggest sticking closely to the +P loads in your manuals and on line loading info.
If you go to http://data.hodgdon.com/cartridge_load.asp for instance, they don't even show a starting load for +P, just max.
I do see an advantage to +P over .357, it's still about half the recoil.

You can load 38 brass to +P loads in your manual. After that, your kinda on your own.

Hi, I joined this forum to answer this question, Don't know if my answer is right but it is what I do. I think he asking if he can load a 38 special to 357 magnum pressures? The short answer is YES, I've been doing it for years, But don't ever shoot any of these hot loads in a 38 special gun or you will likely blow it up, Even it its rated for plus p loads. I shoot mine in my Ruger Blackhawk and my S&W 19's, S&W 27, Ruger GP100, and an old Herters 357 Magnum. All of these guns were built to withstand the pressures of the 357 mag. The 38 Special has a Sammi of 13,500 cup or something like that where the 357 mag has a Sammi of 52,000 cup or somewhere around there. So, you see there is a HUGE difference in cup pressures for each cartridge. But, If your are going to shoot these hot 38's in a 357 mag you can load the 38's to the same cup pressure as the 357 mag but they have to be shot in a 357 mag, one mistake and no more 38 handgun or possibly fingers or whole hand. Now if you really want to load these hot loads then do this. Find a 357 mag load that you want to duplicate, then start at the lowest starting load and then reduce that by 20 percent, since the 38 case is about 15 to 20 percent smaller than the 357 mag. Now work your load up to the max in small amounts until you start to see high pressure signs like flattened primers and or hard extraction. One more thing if the 357 mag load calls for a magnum primer then you will have to use the magnum primers in your 38 special hot loads also. PLEASE be careful working up your loads and make sure to keep them separated from your regular 38 special loads.

although Cuebuilder said you could and gave you specific methods of a safe approach to this, and even he said that if you load them in a .38 by accident you could have serious trouble.
My advice - either load them as a hot .38 (.38 +P) or even as a std .38 and use them for plinking. Then you can get your wife or girlfriend shooting with you. (or both!)

The space below the bullet is the key. Technically it is safe, IF you follow .357 mag load data, AND if you keep the overall length the same that the data specifies. This requires that the bullets crimp groove to be above the case mouth, which means the other five bullets could move when you fire the gun. The only safe way to load a .38 case to .357 mag levels is with a cast bullet that has an extra crimp groove to keep the cartridge at the length of a .357 mag.