Break Top Revolvers

[Clark]

My grandfather immigrated from Sweden to go the Alaskan Gold rush.
On the way he bought an Iver Johnson 38sw hammerless break top revolver that is still in the family.

My father got an EE degree in 1944, got an ME job in 1949 and in a few months had made a long list of patents and sold artillery mostly to Detroit Arsenal that later fought in Viet Nam, like the M55, M107, and M110.

In 2002 my brother and I started buying all the break top Iver Johnson revolver we could at $35 each broken and $50 working. I mostly fixed broken trigger springs.

I started overloading the revolvers to try to blow them up, as I do.

Unlike many revolvers, the IJ break tops have problems before they shoot loose or split the cylinder and break the top strap: the break top mechanism gets loose.

As an example, a 32 acp semi rimmed cartridge fits and shoots in a 32sw antique IJ revolver. But just one shot will make the action loose. There is tiny screw on which the break top latch pivots, 4-56 or something. That screw is captured by a thin piece of sheet metal with two holes in it. The small hole captured by the latch pin will stretch into an oblong shape.

My father said it was caused by bullet friction and recoil acceleration on the mass of the top half of the barrel assembly.

I have a hard time getting my mind around that, but the damage can be avoided with soft Lead bullets and super wimpy powder charges.

 

[Magnum Wheel Man]

BTW... the extractor need not be an issue... I have a couple old H&R's that had a manual extractor ( operates just like a modern double action extractor ) note that short case length is not needed with this design... I have one in 38 S&W & one in 32 S&W Long

 

[micromontenegro]

Let's not forget that NAA made a break top for the comparatively high pressure .22 WMRF. A tiny one. Of course, it was so expensive that they had to call it of after a small production batch.

But they proved it can be done.

 

[Surculus]

I don't remember advocating the manufacture of a break-top .454. I DO recall questioning the premise that a well-designed top-break double-action revolver of modern manufacture were no longer viable defensive arms because they would not withstand the rigors of 30000+ psi cartridges like 9x19, .38Super, .357 SiG, .357 Mag, .40 S&W, etc.
...
The IzMech MP-412 may not be up to withstanding .357 Magnum pressures (35,000 psi) for long stints, but it DOES provide "proof of concept" that the piece might be designed to withstand pressures in the .44 Special/.45 Colt range (14,000 psi) and probably in the .45 ACP spectrum (21,000 psi). Additionally, the use of polymer in various non-critical parts of the firearm might lower production costs even further.

The problem isn't solely about withstanding the cartridge pressure: that isn't the function of the hinged frame, it's a function of hoop strength [terminology?] of the cylinder. Modern materials & design can handle that, just as they've done for solid frame revolvers. The sticky wicket is the ability to withstand the thrust force of the cartridge [base dia. x max. psi] over thousands of rounds fired.

Basically, it's analogous to trying to convert a SxS shotgun into a SxS rifle: there are a lot of variables to consider to make it a safe proposition to begin with, & not waste your time w/ a gun that will beat itself into an unsafe condition in short order.