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Old June 28, 2013, 01:01 AM   #5
Clark
Senior Member
 
Join Date: December 4, 1999
Location: WA, the ever blue state
Posts: 2,994
CAUTION: The following post includes loading data beyond currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The High Road, nor the staff of THR assume any liability for any damage or injury resulting from use of this information.
My poor grandfather had an Iver Johnson break top 38 S&W and black powder cartridges in the Alaskan Gold Rush.
I was buying and torturing 38 S&W revolvers with overloads ~ 10 years ago.
I worked up experimental loads. I worked up to 7.9 gr. Blue Dot 158 gr. JHP 357 bullet [38 Super +P loads], when I noticed that one newer breaktop had developed .003" looseness in the breaktop and an older one had .020".
The failure mechanism is the eye of the latch stretches into an oblong shape.
I had worked up loads .1 gr. at a time, looking for pressure signs.
However, my late father, once chief engineer of a large gun designing operation, snapped at me that the chamber pressure was unrelated to that failure. He said there is no direct pressure affect on the latch. Only the recoil on the upper half of the barrel and the bullet friction add to be the latch stress.
I had to think about this for hours. Most people cannot get it. What it means is that breaktops should only be shot with soft lead bullets.
Never JHP .357.

158 gr. .360" soft lead, 2 gr. Bullseye, good load
125 gr. JHP .357", 6.5 gr. AA#5, too dirty
158 gr. JHP, .357", 4.5 gr. Unique [9mm load] kicks hard in two of the 38 sw revolvers
110 gr. JHP, .357", 5.3 gr. Unique, good load
158 gr. JHP, .357", 7.9 gr. Blue Dot [38 Super +P load], elongated newer gun latch .0035", older gun .020" in 6.2 to 9.4 gr. work up.
158 gr. LSWC 5 gr. Power Pistol, no damage to latch in newer IJ, some leading

The following does not have a break top action with thin latch, but is a swing out revolver:
Colt 38 S&W Police Positive 38 made in 1911 20.5 ounces 4" barrel .7" long 158 gr hard cast .358" bullet 1.299" OAL, RP primed brass
a) 3 gr Unique wimpy recoil
b) 4 gr Unique stiff recoil
c) 4.5 gr Unique obnoxious recoil, tiny pierce in primer
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Last edited by Clark; June 28, 2013 at 01:08 AM.
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