Somebody fact check me.

[Mr_Flintstone]

This makes sense in my head, but I don't know if it works this way in real life.

Ignoring the fact that I can shoot .38 Special in a .357 Magnum, suppose I want to make a .357 Magnum load that is equivalent to a known .38 Special load from a loading manual. If I use the same powder and bullet as the .38 Special load, and step the .357 load down from the minimum charge until it has the same velocity (measured with a chronograph) as the .38, then I should have reliable and safe load data for .38 special in a .357 case.

 

[entropy]

Yeah, it can be done. If you go too low a charge with dense powder, you may have unreliable ignition unless you tamp the charge in place with some polyfill.

 

[Shimitup]

Definitely what entropy said, just thought I'd suggest a bulky flake powder like Unique.

 

[crestoncowboy]

Some powders warn against reducing charges as it supposedly raises pressures. Winchester 296 and h110 are two. There may be more. I usually use unique for reduced loads.

 

[Toprudder]

When working with low charges and large case volume (like 357mag), try to use a powder that is known to be position-insensitive. I like BE86 for this, but if you really want low velocity then Trailboss would be a good one, since it will fill the case.

 

[ArchAngelCD]

Instead of stepping the .357 load down to reduce the velocity to what the .38 Special would be I would step up the .38 Special charge the 1 or 2 grains you will need to equal the .38 Special velocity in the slightly longer case. I suggest this because there are several slower powders used in the .357 which are not appropriate for use in the much lower pressures of the .38 Special.

That said, in the past I have used the max charge for a .38 Special load in a .357 Magnum case and called it good. Of course you will not exactly match the peak velocity of the .38 load but you will be very close.

 

[Blue68f100]

I do that all the time, just make sure you get the softer 12 BH bullets. Like said some powder are sensitive to position. I use WST for this, usually bump the charge by 0.1-0.2gr to make up the difference in case volume.

 

[AZAndy]

My favorite target load for .357 is a .38 style load. I do 5.2 grains of Unique with a 158gn LSWC. Very comfortable to shoot. Chronographs at about 800fps with a 4" barrel.

 

[Varminterror]

10% greater charge than known 38spcl = roughly the same in 357mag cases. Have to be sure your powder is flexible, but it’s a known method.

 

[reddog81]

There are a number of powders with .38 Special and .357 Mag load data. Use any of those and you should be OK using your method. There are some powders were this would not work out well, but anything with loads for both cartridges will be fine.

Anything from a max .38 Special charge to a min .357 charge will be OK in a .357 Mag case. Using starting .38 Special loads in a .357 case could cause problems.

 

[Walkalong]

Instead of stepping the .357 load down to reduce the velocity to what the .38 Special would be I would step up the .38 Special

This, and use .38 Spl appropriate powders.

And actually you can just use a max .38 Spl load in .357 brass without issue. Look for a little velocity loss, but not much.

And with some powders you can safely load .357 Mag cases down to very light .38 Spl levels. It needs to be fast, bulky, and not particularly position sensitive. I use WST or Competition for this. Both work very well and will not stick a bullet even when the powder is forward against the bullet/away from the primer when running a plated 158 Gr SWC around 700/750 FPS (Depending on the barrel length) from .357 cases. Accurate, clean, fun, easy to shoot all day.

 

[Reeferman]

Use the powder that is used for 38 in 357 cases and you will have no issues. Do not download magnum powders such as 110 and 296 which are not listed in 38 data anyways. I’ve loaded and shot 1000’s of 38 special loads in 357 cases mostly with 231 and Bullseye.

 

[Mr_Flintstone]

OK. So better to step up .38 Spl data than step down 357. The .38 Special powders (for 158 gr lead bullets) I have on hand right now are Bullseye, Titegroup, Autocomp, IMR4227, and Trail Boss (which is already at .38 levels when loaded in a .357.)

Of those (excluding Trail Boss), which would be the best to start with, or which should I avoid?

 

[kcofohio]

10% greater charge than known 38spcl = roughly the same in 357mag cases. Have to be sure your powder is flexible, but it’s a known method.

That is what I have done in the past. And it has worked well.

 

[Toprudder]

OK. So better to step up .38 Spl data than step down 357. The .38 Special powders (for 158 gr lead bullets) I have on hand right now are Bullseye, Titegroup, Autocomp, IMR4227, and Trail Boss (which is already at .38 levels when loaded in a .357.)

Of those (excluding Trail Boss), which would be the best to start with, or which should I avoid?

Of those, I would say Titegroup, then Bullseye. I think Autocomp is too slow, and I don't think IMR4227 is happy unless it is close to a full magnum load.

 

[tightgroup tiger]

Of the powders you mentioned I also would go with Titegroup if I wanted powder puff loads.

 

[Bfh_auto]

That is what I have done in the past. And it has worked well.

Same here.

 

[Barry loyd]

Do it all the time. 4 gr Titegroup over a 158 LSWC. Gnat farts.

 

[Walkalong]

OK. So better to step up .38 Spl data than step down 357. The .38 Special powders (for 158 gr lead bullets) I have on hand right now are Bullseye, Titegroup, Autocomp, IMR4227, and Trail Boss (which is already at .38 levels when loaded in a .357.)

Of those (excluding Trail Boss), which would be the best to start with, or which should I avoid?

4227 is unsuitable, too slow. Autocomp will work for upper end (Maybe a little less) .38 Spl type loads in .357 brass.

Titegroup or Bullseye are what you want for very light loads.

 

[ArchAngelCD]

And actually you can just use a max .38 Spl load in .357 brass without issue. Look for a little velocity loss, but not much.

I agree and said the same in the last two lines of my post. Great minds think alike lol...

 

[ArchAngelCD]

OK. So better to step up .38 Spl data than step down 357. The .38 Special powders (for 158 gr lead bullets) I have on hand right now are Bullseye, Titegroup, Autocomp, IMR4227, and Trail Boss (which is already at .38 levels when loaded in a .357.)

Of those (excluding Trail Boss), which would be the best to start with, or which should I avoid?

Exactly, you already have your answer and solution. AutoComp will give you some room at the top in case you need to find an accurate load.

 

[Reeferman]

OK. So better to step up .38 Spl data than step down 357. The .38 Special powders (for 158 gr lead bullets) I have on hand right now are Bullseye, Titegroup, Autocomp, IMR4227, and Trail Boss (which is already at .38 levels when loaded in a .357.)

Of those (excluding Trail Boss), which would be the best to start with, or which should I avoid?

You don’t need to go over max load for 38 special to make it work in a 357 case. One of my most accurate light loads is 3.5 grains of Bullseye with a lead or plated 158 grain bullet.