Rimless rimfire?

[Henry Bowman]

Has there ever been a rimfire round made in a "rimless" configuration (like an ACP cartridge)?

Rimfire rounds (like .22LR) are hard to feed with a "push" spring magazine holding more than 10-20 rounds because of the larger diameter rim. If a case could be made with a groove for extraction, but with the "rim" no greater in diameter than the body of the case, we could have small caliber, low cost, easy to feed ammo. The primer material would be spun into place the same way current rimfire ammo is made.

Has this ever been tried?

 

[Jim K]

It won't work because the rim containing the priming has to be supported in order for the firing pin to ignite the primer properly and consistently. In other words, the primer has to be "pinched" between hard surfaces (firing pin and chamber edge) to fire properly. If there were an extraction groove, the firing pin would just bend the rim over; there would not be enough support.

I suppose a gun could be designed with some kind of collet that would fit into the groove and provide support, or the firing pin could be put under the extractor so the latter would provide support. I don't know how practical those ideas would be; I think we are stuck with a rim on a rimfire cartridge.

Jim

 

[Chipperman]

How about a moon clip to hold the rounds? That would also give support for ignition. Why would you want this though?

 

[Zero_DgZ]

Erm. Wouldn't a moon clip completely negate being able to put the things in an autoloader?

I mean, a moon clip is designed to take rimless rounds and use them in a gun that wants rimmed ones; The idea of inventing a rimless round to replace a rimmed one and then using a moon clip to convert it back into a rimmed round is patently absurd...

 

[Chipperman]

The idea of inventing a rimless round to replace a rimmed one and then using a moon clip to convert it back into a rimmed round is patently absurd...

Right, which brings to me the question of why you would want it. My comment was about making a rimless rimfire work, not for use in an autoloader.

 

[Fred Fuller]

http://en.wikipedia.org/wiki/American_180

http://www.thefiringline.com/forums/showthread.php?p=153588
I seem to recall a belt-fed .22LR that Williams made- saw video of it once upon a time? Being a rimmed round didn't slow that one down one whit...

lpl/nc

 

[sparky2726]

with proper metalergy (sp) and construction of the brass, its possable. The back side of the rim would have to be strong enough to not bend against the fireing pin, and the other side soft.

I would think, however, due to the complicated manufacturing process, it would be just as expensive, or more so, than a standard center fire round.

Sparky

 

[Henry Bowman]

Just wondered if it had ever been done.

There are 2 ways to feed rounds in an autoloader: Push (spring in a box magazine, including a Ruger 10/22) or pull (belt fed). Pushing a rimmed cartridge is limited in number. At some point (about 20 rounds), you cannot reliably push a stack of rimmed cartridges.

Rimfire rounds are cheaper to make (and shoot) than a centerfire round with a separate primer. So long as the cost of making the casing does not completely off set it, it could be a good (fun) thing. Seems like it wouldn't cost any more to make than the hollow rimmed shell of .22LR. Think: cheap to shoot full auto.

The entire rim would not have to be supported in the chamber, just the part where it will be struck.

The American 180 was a great idea, put required a pretty pricy "cassette" magazine that never caught on.

 

[Jim Watson]

I can visualize a couple of approaches that might work but the whole thing presupposes a large market for a high capacity plinker. Which might not be there and which may not be legal much longer.

American Commoners are not permitted new manufacture full autos and their taxes pay for centerfire ammo for government agents' guns so there is no incentive there to reduce the cost of autogun ammunition.

 

[Lucky]

If there was 5.56 rimfire in Canada then we'd be able to buy magazine for it with capacities greater than 5. And once you have the magazine you can use it in any firearm you like. So there'd be a great demand, if you had a rimfire round the same size as any common center-fire round.

 

[Henry Bowman]

but the whole thing presupposes a large market for a high capacity plinker. Which might not be there and which may not be legal much longer.

Excellent point. Sure glad John Moses Browning didn't have to face that sort of disincentive.

 

[gezzer]

If it doesn't have a rim it cannot be a RIM fire.

 

[Chipperman]

OK, how about we call it "Edge-fire"?

 

[Novus Collectus]

Has there ever been a rimfire round made in a "rimless" configuration

Why yes, yes there has.

 

[Pax Jordana]

http://en.wikipedia.org/wiki/American_180

http://www.thefiringline.com/forums/...d.php?p=153588
I seem to recall a belt-fed .22LR that Williams made- saw video of it once upon a time? Being a rimmed round didn't slow that one down one whit...

lpl/nc

275 rd .22 short drum mag!!

I can picture the 24th-century bionic-thumbed riot cop.. or-

"hey rookie... go load some more magazines"

 

[Novus Collectus]

Has there ever been a rimfire round made in a "rimless" configuration

CUPFIRE CARTRIDGE - A front-loading rimfire cartridge used in early pistols which were designed to circumvent the Rollin White bored-through cylinder design. The fulminate was distributed around the concave base of the cartridge. Known in .28, .30 and .42 calibers. Probably made by Phoenix or American Cartridge Companies. Some have raised A or P headstamps.

The primer was in the rim, but it was on the inside rim of the cup shaped base. I have only seen drawings, but they show that there was no externaly protruding rim (i.e. rimless) and I am sure this is so since it was fed from the front of the cylinder.

And there was also this "rimfire":

CRISPIN CARTRIDGE - A distinctive type of rimfire cartridge where the fulminate is contained in an annular ring nearly midway between the base and mouth of the cartridge. The most common type is the .50 caliber version intended for use in converted Civil War Smith Patent carbines. It is also known in .44 and .31 calibers. Patent #49,237, 8-08-1865.

http://www.cartridgecollectors.org/glossary.htm

After hundreds of years of firearm development, just about everything has already been tried, thought of, or manufactured.

 

[Jim Watson]

One of the Army fletchette gun prototypes was a cup-fire design, too. Maybe the Steyr.

On a .22 Edge-Fire you are going to have to control headspace somehow. Use of an inside lubricated or jacketed bullet in a crisp taper crimped mouth will run the cost up. Most .22 lr match rifles engrave the bullet into the rifling, maybe that would be good enough in an auto. Or if it could be made as a faint bottleneck.

 

[griz]

You could do it as long as the pressure was kept to rimfire levels. Imagine starting with a brass "cup" that was straight and cylindrical. Then an extractor groove is turned into the bottom end to form the body diameter rim, the other end is bottlenecked to allow headspacing, and you have a rimless rimfire.

I think you would also have something that nobody would buy. It would have to cost more than the new 17 rimfires since it would have to overcome the same hurdles as they did to pay off development costs. It's hard to overcome the economy of scale that the 22 LR has.

 

[Jim K]

"The entire rim would not have to be supported in the chamber, just the part where it will be struck."

Hmmm. And how would you ensure that the cartridge was properly aligned in the magazine so that that part of the rim would always come under the firing pin.

I was going to bring up the cup fire, lip fire, pin fire and other "rimless" rounds, but things have gotten silly enough at this point.

Jim

 

[armedandsafe]

I envision a folded case design, with the primer material spun into the "rim" and flowing around the entire circumferance, just as it does in a standard rimfire case. The arm's extracter fits into the extractor groove and acts as the support for the rim at the point the (offset) firing pin strikes the rear of the case. The case is headspaced on the extractor to bolt dimensions.

How many things did I get wrong?

Pops

 

[SDC]

Benelli once built an SMG that operated sort of in the way you're describing, using a proprietary round called the 9mm AUPO; this was a case and bullet all in one, with the bullet having a skirt that was drawn down into a cup, so the propellant and priming compound could be contained in that cup, but everything was expelled from the bore on firing; these used an internal priming system similar to the rimfire/Flobert system, but placed so that the hammer/striker had to hit the SIDE of the cartridge. For extracting an unfired round, the rear of the skirt was turned inwards slightly so a hook on the bolt could withdraw a live cartridge.
http://translate.google.com/transla...=/search?q=9mm+AUPO&num=50&hl=en&lr=&safe=off

 

[Zundfolge]

Henry, I guess I fail to see the point in making this "rimless rimfire".

The ONLY purpose for rimfire to exist today is that its cheap to manufacture. Development of a new type of centerfire would eat up any cost savings, and I doubt an ACP type cartridge with a rimfire type primer in the rim would be cheap to produce. Plus its less reliable than centerfire, its not capable of being loaded as hot as centerfire, and there are already actions built around a centerfire cartridges to do pretty much anything you want.

You'd be better off developing a centerfire .22lr (maybe a .25acp necked down to .22)

Oh yeah, I forgot about the 5mm Remington Centerfire Magnum

 

[c_yeager]

The reason for the popularity of rimfire ammunition is that it is cheap, making it more expensive defeats this purpose. It would make more sense just to make a very small centerfire cartridge to do the same job.