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Thread: Reload .357 to .38 spec?

  1. #1
    Junior Member
    Join Date
    Dec 2012

    Reload .357 to .38 spec?

    I know .38 can be shot in .357 as a light target/plinking round.

    What do you recommend as far as loading .357 cases using .38 reloading specs?

    I also know I could simply re-load .38, but then I would have two different cases to keep track of.

    Thank you in advance!

  2. #2
    Member TurboHonda's Avatar
    Join Date
    Aug 2012
    Flyover, USA
    Welcome to the forum. Since you didn't indicate otherwise, I will assume you are new to reloading. Therefore, I recommend that you not stray from the loading manuals.

    I have never found a reason to load magnum cases with sub-velocity loads. Keeping track of different case sizes seems easier than keeping track of light magnum loads. Also, small powder amounts in large cases is inviting inconsistency due to the vector angle of the fire arm. Of course, you could use inert ingrediants (such as corn starch) to hold the propellant against the primer, but that would be deviating from the loading manual.

    Good luck and welcome.

  3. #3
    Member high pockets's Avatar
    Join Date
    Apr 2011
    Georgia, for now
    Welcome to the forum!
    TurboHonda likes this.

  4. #4
    Senior Member Steve M1911A1's Avatar
    Join Date
    Feb 2008
    Northwest Washington State
    The .38 Special case measures 1.16" in length.
    The .357 Magnum case measures 1.29" in length.
    The difference is 0.13", or about 1/8".
    (That is, not much.)

    By carefully choosing the correct, recommended powder, and the recommended bullet, you can easily construct .38-Special-strength loads which will operate perfectly well in .357 Magnum cases.

    The first thing I thought of, in such a case, is Trail Boss powder, the correct load of which is usually about a case-full (without compression). Trail Boss powder is used by Cowboy-Action shooters to produce black-powder-like loads (that is, low recoil) in both old and modern cases, measuring by charge volume rather than by charge weight.
    There are other powder choices which will produce low-recoil loads from almost-full .357 Magnum cases. Any modern loading manual can help you find and construct them.

    One way to begin would be to find a .38 Special load which is noted as producing low to moderate recoil. Then note both the bullet weight and the load's published velocity, and look in the .357 Magnum listing for the same bullet weight and velocity.
    Just use that load. It'll work fine. The extra 1/8" of case length will make no difference with most modern powders. But if it really matters to you, fill the empty part of the case with Cream of Wheat cereal, or even with loosely-wadded toilet paper.
    hillman and Bisley like this.

  5. #5
    HGF Forum Moderator
    DJ Niner's Avatar
    Join Date
    Oct 2006
    North-Central USA
    I did something like this for many years, but I never just dropped a .38 Special powder charge into a Magnum case; I always used a manual to pick out a light Magnum load for whatever bullet weight and style I wanted to use. I used the Lyman Reloading Manual for many of these loads (I think the older Speer reloading manuals also had some listed), but the manuals I have are decades old, so I don't know if the current versions still show these lighter Magnum loads. If not, many older reloading manuals can often be found at gunshows, swap meets or online.

    I usually used a swaged-lead bullet in light target loads, a cast-lead bullet in medium-power target or hunting loads, and jacketed bullets in all full-power Magnum loads in both my .357 and .44 Magnum ammo, so I didn't have to worry about accidentally grabbing the wrong power-level ammo when I went shooting; a glance at the bullet told me what I had in hand, power-wise.

    The nice thing about using only full-length Magnum cases for loads of all power levels is you don't end up with the ring of built-up fouling in the chambers from using the shorter cases, which has to be removed before you can shoot Magnum-cased ammo (or it can raise pressures and/or cause the cases to stick in the chambers after firing).
    Steve M1911A1 and Bisley like this.
    "Placement is power" -- seen in an article by Stephen A. Camp
    (RIP, Mr. Camp; you will be remembered, and missed)

  6. #6
    Junior Member
    Join Date
    Dec 2011
    God, it has been done for decades, but manuals don't usually show such data.
    Go to Cowboy Action loads and look at .357 Mag data. You'll probably work UP from there.
    Use starting .357 Mag loads and work down, and, generally, using powders no slower than AA5.
    Even if you start with .38 Spl starting loads, there is more than enough powder to get bullet to exit the barrel.
    All you want is an accurate and easy-to-shoot load, more than you want to duplicate a particular .38 Spl load, I assume.

    For example, Alliant shows the following:
    .38 Spl Cowboy Action
    140gn Hdy L-FP: Am. Select 4.5gn MAX at 988fps
    140gn Hdy L-FP: Unique 5.5gn MAX at 985
    No 158gn bullets tested.

    .357 Mag Cowboy Action
    140gn Hdy. L-FP: Am. Select 3.6gn MAX at 825fps
    140gn Hdy L-FP: Unique 4.0gn MAX at 820fps
    158gn L-RN: Am. Select 4.0gn MAX at 840fps
    158gn L-RN: Unique 4.5gn MAX at 859fps

    General rule is to reduce the MAX load by 10% for starting load.
    Then, they don't use the 140gn Cowboy bullet for std. loads for either and no 158gn loads in.38 Spl., but for .357 Mag they show:
    158gn L-SWC: Unique 6.0gn MAX at 1034fps
    (It would be nice if the same bullets were used for comparison)

    I didn't like firing a lot of .38 Spl in my .357 Mag as I didn't like cleaning the cylinders so .357 Mags would drop in again. However, it has been decades since I did so.

  7. #7
    Junior Member
    Join Date
    Jul 2015
    I reload 38 pressures into 357 brass. Prevents the burn ring in your cylinder and prevents the difficulty of loading 357 afterwards. Been doing this for 25 years with no problems.

    Makes the round a lot friendlier to kids and the ladies...along with the older folk who don't care for sprained wrists.

  8. #8
    Junior Member
    Join Date
    Dec 2012
    Thanks for the replies!

    I'm not new to reloading, but I've never strayed from my Hornady manual.

    I can see the concern about using a lot of short brass in the cylinder now.

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