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.38 in Iver Johnson

Discussion in 'Handguns: Revolvers' started by Grayrock, Jun 17, 2021.

  1. Mauser lover

    Mauser lover Member

    Jul 13, 2011
    East KY
    Yeah, good point. I didn't state this clearly enough before.

    Before I start, all numbers are approximate, and chosen to lessen my workload.

    Argument #1, volume of the pressure vessel

    A full power round lodging at the very end of the muzzle is not the same as a full power round being stopped right in front of the cylinder. If round #1 is a (primer only) squib on a .38 special, it is probably only going to go an inch down the bore. Round #2 is full power and rams right into bullet #1 just in front of the cylinder gap. You end up with the drawing from Kuhnhausen's book.

    A weak reload that travels 1/2 of the way down the bore before stopping is not the same as the previously mentioned squib. Round #1 is a weak reload and round #2 (full pressure) hits it and in a .38 special bulges the barrel.

    Example number 1, in .38 Special. If the squib travels 1" before sticking, you have .100098 cubic inches of bore behind it and .150148 cubic inches of cylinder. This equals .250246 cubic inches that the next round needs to pressurize before bad things happen.

    Example number two, also .38 Special. If the underpowered .38 Special handload travels 2" down the barrel before sticking, we have .200196 plus the same .150148 cubic inches, equaling .350344 cubic inches that the next round needs to pressurize before bad things happen. This is 140% of the volume that the squib example allowed us before bad things happened to that one.

    Example number three, the OP's conundrum. My lemon squeezer has a 3.25 inch barrel and a 1.25 inch cylinder, so we'll pretend that the OP's barrel and cylinder are the same length. If the bullet lodges in the last .5 inch of barrel that gives a nice 4 inches. (4) (3.1416) (.03258025)= .4094 cubic inches of pressurization before bad things happen. A larger pressure vessel means less pressure overall, and this is 117% of the volume of the previous underpowered handload example that didn't blow up the gun (all the way).

    Argument #2, volume of the charge

    Consulting my ancient Lyman reloading manual (1964) and comparing the charges for .38 S&W vs .38 Special...
    Recommended loads in this manual, comparing only identical bullet weights and powder type, demonstrate that (right or wrong) in 1964 Lyman recommended that folks load anywhere from 17% to 50% less powder in .38 S&W than .38 Special. 17% to 50% less powder produces 17% to 50% less gas volume when combusted (assuming all the powder combusts).

    Argument #3, volume of the leakage

    In addition to the volumes in question, we also need to address the time spent before pressure starts to build more than the designers expected. Why? Because revolvers leak, and not an insignificant amount. Example number two leaked twice as much as example number one (assuming constant bullet speed, which is not correct, but should be close enough for today). Example #3 (.38 S&W) would have had 275% the leakage as the first, and 137.5% of what example #2 had; if this bullet was travelling as fast as the .38 Special cartridges-which it won't. Maybe add 10% leakage just because the bullet is slower.

    So... I think Argument #2 does not logically apply to what you brought up. However, I believe arguments #1 and #3 to be logically valid (not necessarily correct, just logically valid) regarding this particular question. Since I already went to the trouble of digging out my handloading manual and typing it up, I figured I should leave it.

    Thoughts? I'm sure I missed something, so please let me know what you see.

    To be clear, my recommendation to the OP or anyone in his shoes is to bolt a vise to a sawhorse, clamp the revolver in the vise, load one fairly low pressure (but within the recommended range) .38 S&W cartridge (black powder, if need be), tie a string to the trigger, and hide behind the truck when you fire it. Check to see if the bullet lodged at the end of the barrel. If not (which is what I expect), and after subsequent testing you believe the revolver to be reasonably safe, I would use the firearm as intended by the manufacturer. Also, check to see if the latch is loose. These top break revolvers can stretch a bit.

    Edited because I'm incompetent...
    Last edited: Sep 28, 2021
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