Disarm a 100 year old rifle round

[Mike Irwin]

At close range the primer cup can do a fair amount of damage.

When I was working for American Rifleman in the early 1990s we got a letter from a guy who took a misfire, pulled the bullet and powder, and then started heating the case head with a propane torch in preparation for soldering something to it.

The primer was "dead" to the strike of a firing pin, but it wasn't dead dead. When it went off the force of the explosion drove the primer cup through his chest, between two ribs, and into his lung. He had to have it surgically removed.

[Unclenick]

That reminds me that Garand's first semi-auto rifle design was primer actuated, getting enough force from the primer backing out to drive the bolt back to eject the fired case, cock the firing mechanism, and compress a spring enough to return the bolt to load load the next round. He had to abandon the design when the military decided to start crimping primers.

[Mike Irwin]

"getting enough force from the primer backing out to drive the bolt back to eject the fired case"

Are you sure about that?

The way I understood that rifle to work was that the primer setback UNLOCKED the bolt, after which cartridge setback completed the firing and reloading cycle.

[Unclenick]

You could be right. It's probably been a decade since I read about it. My recollection is the term used was "primer actuated", but I'll look it up. No point in me spreading misinformation.


Later:

Page 4 of Hatcher's Book of the Garand (he does call it "primer actuated" and, later, "primer operated") shows what appears to be a coaxial sub-bolt within the bolt-proper that blows back to unlock it. So, you appear to be correct, and I apologize for not checking before writing the previous post. It still takes some force, though, to unlock the bolt against pressure. I'm guessing the sub-bolt mass and spring tension are critical to the timing, as you can't have the fired case subsequently pushing too hard or too little on the bolt. It may have been picky about ammo?

[Mike Irwin]

"shows what appears to be a coaxial sub-bolt within the bolt-proper that blows back to unlock it."

That's exactly what I remember.

If properly manufactured and designed, it actually wouldn't require all that much force as you could multiply the primer thrust mechanically with the design of the sub bolt.

The main bolt would be taking all of the backthrust of the cartridge at that point.

I know Garand designed several rifles using this type of operation, the first one or two used a rotating bolt head, while the third used, IIRC, a solid bolt that tilted into a recess in the receiver.

The case pushing too hard on the bolt would be more a function of overall cartridge pressure, I would think, and would be critical to the operation of any semi-automatic rifle.

[Unclenick]

Yes to the multiplier. The inner bolt has an internal ramp cut to add mechanical advantage to its rearward thrust. Sine of the angle multiplier. Its return spring shows straight compression, though.

Were you thinking maybe Garand had a tilting locking bolt like the Marlin machine gun? Could be. I'll have to give the Book of the Garand a complete reread. It's been too long.

[Mike Irwin]

No, the Garand does not have a tilting bolt, it has a rotating bolt. Bolt rotation is, however, not extensive. When the op rod starts back, it works on a cam surface on the bolt which rotates the locking lugs out of engagement with the receiver and allows the action to open.

Garand's early designs used a rotating bolt head and tilting bolt, but at some point he apparently abandoned that in favor of the rotating bolt that the M1 uses, probably around the same time that he abandoned the concept of primer actuation.

I've never measured it, and it's been awhile since I've seen one in slow operation, but I really don't think the Garand bolt rotates much more than 30 or 40 degrees.

[Unclenick]

Originally Posted by Mike Irwin

. . . the first one or two used a rotating bolt head, while the third used, IIRC, a solid bolt that tilted into a recess in the receiver.

That's where I got the idea you were speaking of a Marlin machine gun type bolt or its analog? I really will have to reread the development chapters in the Book of the Garand. When you look at how few parts the final Garand design employs as compared to the designs that competed with it for selection, his ingenuity is impossible not to admire.

[Mike Irwin]

By Marlin machine gun, are you talking about the Browning designed Model 1895, which was manufactured by Marlin for a number of years?

I'm not sure how the bolt operated on that one.

[Unclenick]

Hatcher says only that during WW I, Marlin modified the 1889 design that Browning did for Colt, then refers to it as the Marlin Machine Gun (Hatcher's Notebook, pp. 56-58; he illustrates the operating principle on page 57). When you mentioned the tilting bolt, I'd remembered Hatcher had that illustration somewhere early in the book and leafed through until I found it. Hence my reference to it. He didn't separately illustrate the Colt that I can see, so we'd probably have to go back through the old patent drawings to see how modified it actually was?

The mechanism has a gas piston op-rod, not dissimilar to the Garand's in principle, having a forward gas cylinder and piston and a forward operating rod spring. The difference is that instead of a camming slot rotating the bolt to unlock it before pushing it into counterbattery, it has what are either one or two (can't tell from the diagram) wings on the underside of the back end of the bolt with the arc of the camming slot(s) cut into it (them). A pin through the back of the op-rod engages the slot(s) so that when the rod moves to the rear, the slot(s) ride the pin to lift the back of the bolt up out of a locking recess before pushing it into counter battery. The bolt face then is slanted to make up for the fact its back end is tipped down into the locking recess when it is in battery.

[mapsjanhere]

Mythbusters had a nice set of tests on bullet going off not in the barrel in their "bullet in the oven" episode. In each test, the case actually did more damage than the bullet. And even an exploding .50 BMG wasn't able to penetrate the glass front of the oven. I'd say the round is fine as it is.

[Mike Irwin]

OK, Marlin Rockwell took Browning's design and replaced the reciprocating under barrel lever with a gas piston and produced it under their name.

I can't find schematics for the Browning-Colt.

When I worked for the Pennsylvania Museum and Historical Commission in the 1980s I assembled two Colt Brownings from parts in the military history collection. One went to Boalsburg to the 28th Division Museum and Shrine and the other is still in collections in Harrisburg. I'll be damned if I can remember exactly how they worked.

[Unclenick]

That swinging under barrel lever is the only thing I remember about the Colt, and recall thinking you would want to keep your hands clear. I saw at least one used in a movie, too, about striking workers being fired on, IIRC?

Hatcher turns out to have more on the Marlin on page 82. Apparently it was developed (by a fellow named A. W. Swebilius) because there was no way to synchronize the Colt with aircraft propellers. The swing arm apparently regulated it and kept the action very smooth, but I suspect, like a pendulum, it also made it keep its own time. The Marlin seems to have had some difficulties, including that the chamber had to be cut 11 thousandths short because the gun chambered rounds so hard it could resize them until the headspace was excessive. The gas piston also had to be weighted to slow it to prevent it from tearing the heads off cases. Seems like something of a war time kluge-together.