John Farnam on 9mm Revolvers
BY Herschel Smith
2 weeks ago
During an exercise, shooting factory 115gr hardball from a well-known and reputable manufacturer, a bullet jumped forward far enough to protrude from the face of the cylinder and thus prevent the cylinder from rotating normally. In fact, the bullet jumped forward far enough to physically separate from the case. This not only precluded the revolver from continuing to fire, but it also made it impossible to swing out the cylinder, so the revolver could now not be reloaded!
Honestly I had never considered this failure mode before. But after all, the 9mm cartridge is a rimless cartridge, so one should maybe expect to see this from time to time.
However, I’ve never seen this failure when Jerry Miculek is shooting his S&W 9mm revolver, and he likes his a lot. In fact, he broke one world record with it.
But Jerry uses moon clips. I cannot see how this failure mode could occur if you’re using moon clips.
If any smart gunsmiths care to explain how this failure could happen while using moon clips I’ll listen. But absent such an explanation, I assume that using moon clips prevents this failure mode.
Read the rest of John’s analysis here.
On April 28, 2024 at 8:48 pm, Ol'Pappy said:
Tapered crimp, generally non-factory reloads. Back in the day, we ALWAYS roll crimped revolver cartridges. PPC and combat pistol. Factory crimp dies have eliminated this generally. Had it happen in many S&W 45acp revolvers. There have never been many 9mm revolvers out there so it was never quite so common to hear about the problem. Customers would come in for a quick fix on Saturdays, eat the free donuts and coffee and we’d fix them up. Cheers!
On April 29, 2024 at 4:48 am, jrg said:
I never considered that possibility. The only 9mm revolver I have is a S&W 547 4 in. square butt (I would have much preferred the 3″ round butt version but they were already sold out iirc).
Does the same apply to the .45ACP revolvers ? I’ve shot quite a bit of that in a S&W 1917 Brazilian Police model and never had a problem in the past. Current ammunition may be different.
On April 29, 2024 at 10:13 am, Frank Nobody said:
Jerry isn’t using factory ammo. He undoubtedly crimps his ammo. (Plus he’s not using an alloy super-lightweight revolver, either.)
You can’t roll-crimp a 9mm for an autoloader, since it headspaces on the mouth.
Jerry’s ammo probably won’t work in anything BUT a revolver. Which isn’t an issue for someone doing what he does.
The moon clips don’t have anything to do with it.
On April 29, 2024 at 10:27 am, Herschel Smith said:
@Frank,
It may be true that Jerry is doing his own special thing in reloads, but the presence of a moon clip would indeed prevent bullet jump.
On April 29, 2024 at 10:33 am, Ned said:
I’m not sure how a moon clip would preclude a bullet from migrating out of the case. I have impact bullet pullers that hold the base of the cartridge case and the bullet comes out of the case with a few swats. However, it takes a pounding to remove a bullet crimped with a Lee factory crimp die or a revolver bullet with a roll crimp.
On April 30, 2024 at 11:57 am, Don W Curton said:
Yeah, the others are right – revolver ammo (especially magnum loads) always require a pretty stout crimp while auto-loaders do not crimp since they headspace on the mouth. The moon clip has nothing to do with it.
To look at it in detail, a .357 round has the ends of the case actually bent into a crimp groove in the bullet itself. Thus for the bullet to pull loose, the metal at the case mouth has to bend out straight again – takes some serious force. More force than normal recoil.
For a 9 mm (45 auto, etc.), the bullet is only held in by friction between the case and the bullet. There’s no crimp, no bent metal. If the force of recoil can exceed the force of friction, the bullet being heavier will start coming out of the case. i.e. the lightweight case will move first before the heavier bullet moves.
When used in an autoloader, the bullets are held in a magazine, generally lower than the muzzle and don’t experience the full force of recoil. In a revolver, the bullets are higher up, closer to the chamber and above your grip. They see more recoil even with the same loading due to position.
I have a 45 auto revolver from the 1910’s, don’t shoot it very often but I’ve never experienced that problem myself. However I only use very light target handloads in that gun due to age. I really don’t see the need or utility for a modern revolver chambered in 9 mm, but then again I’m not sitting on a stash of 100,000 rounds of 9 mm like some people.
On April 30, 2024 at 12:01 pm, Don W Curton said:
Just to be clear, my understanding of these malfunctions is that the bullet is actually separating from the case. The case is not creeping forward as a whole – which may be what you’re thinking. I would think with dual caliber revolvers that the 9 mm cylinder would actually have a groove in it for the case to head space on, otherwise a moon clip is required (as with my ancient 45 auto revolver).
On April 30, 2024 at 10:03 pm, Herschel Smith said:
If readers are right and it’s a case of the bullet migrating out of the case, then moon clips as I suggested would do not good at all.
Perhaps reloading is your only option unless there is such a thing as revolver-specific rimless cartridges straight from the manufacturer.
His article didn’t exactly make the failure mode clear. At least, not to me.
I always enjoy learning about new failure modes.
On May 1, 2024 at 4:36 pm, X said:
Moon clips would not affect this at all. The bullet had insufficient crimp. If it was cheap 115 bulk hardball, that stuff is usually plated, not jacketed. Plated bullets can be more difficult to get a good taper crimp on.
I taper crimp revolver cartridges all the time. In fact, a .356″ 125 cast lead 9mm bullet works great for plinking in a .38 revolver if you taper crimp it sufficiently.