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Inky-
10-06-2000, 01:32 PM
Anybody know why small caliber bullets (.22, .25) only come in rim-fire while larger caliber's are center-fire? Any reason for this?

Opengrave
10-06-2000, 01:43 PM
I can't guarantee ths but it mostly has to do with reliability. Centerfire being MUCH more reliable than rimfire. I can explain in greater detail but I can't guarantee any info - its basically my own recollection of reading stacks of gun books.

mrblue92
10-06-2000, 01:46 PM
Economy is one reason. The larger the shell, the more expensive it is. You can reload centerfire cartridges, but not rimfire. Rimfires are cheap, throw-aways.

pluto
10-06-2000, 02:24 PM
I'll second mrblue. A .22 shell is a one-piece, stamped item. A center-fire cartridge requires at least a hole punched for the primer, if not more elaborate machining.

The presumption is that a .22 is a kid's rifle, good for target practice, etc., but not for real hunting, so make it cheap to operate, I guess.

IIRC, the M-16 was (is) a small caliber weapon. Did it use rim-fire cartridges?

Opengrave
10-06-2000, 03:00 PM
M16 is a .223 and is center-fire. I am aware of only a very few rim-fire cartridges and none of them are from the latter half of this century. The only one currently in any widespread use is the .22.

Joe_Cool
10-06-2000, 03:24 PM
First off, .25 ACP (the most common .25 cal. round) is always centerfire. .22 short, .22 lr, etc are rimfire, but the .22 magnum round is centerfire.

The M-16, AR-15, Mini-14, etc are all .223 cal. which is a small, light, but very powerful centerfire cartridge (Mine are loaded to slightly exceed 3000 fps).

As for the reason, .22 is a very small slug with a very small amount of powder. Rim-primer is not only cheaper, but is not as efficient as a Centerfire primer at igniting a large amount of powder.

Larger caliber rounds have much larger casings which hold much more powder. Which requires a larger, hotter, centrally-located discharge from the primer to cause it to burn properly and evenly.

For the record, it is much cheaper to buy a box of factory-loaded rimfire .22's than to try to reload them, but efficiency at igniting the powder is the far greater concern when designing your cartridge. Economics of reloading are a minor, distantly secondary concern.

===WAG ALERT===
It seems to me that rimfire guns don't require as much precision as centerfire, enabling them to use cheaper parts and cheaper manufacturing methods. I could be wrong on that, but it's ok because it's just a guess.
===END ALERT===

GaryM
10-06-2000, 03:41 PM
Joe_Cool,
The Ruger Single Six Convertible revolver I had used either .22 long rifle (rimfire) or .22 magnum (.22WMF?) rimfire cartridge. The S & W revolver I had that was .22 Jet was centerfire. I don't recall a .22 magnum centerfire.

Another reason .22s can be rimfire is because of the lower pressures involved. The brass used in a centerfire case is considerably thicker that that uesed in rimfire cartridges.

mrblue92
10-06-2000, 04:06 PM
Another reason .22s can be rimfire is because of the lower pressures involved.ISTR the .22 generates close to same pressure (18,000-20,000 psi) as many rifles.
Economics of reloading are a minor, distantly secondary concern.Not in the performance arena, I'll agree, but you can bet it is a concern for the sport shooter. :)

Joe_Cool
10-06-2000, 04:10 PM
Originally posted by GaryM
Joe_Cool,
The Ruger Single Six Convertible revolver I had used either .22 long rifle (rimfire) or .22 magnum (.22WMF?) rimfire cartridge. The S & W revolver I had that was .22 Jet was centerfire. I don't recall a .22 magnum centerfire.

Another reason .22s can be rimfire is because of the lower pressures involved. The brass used in a centerfire case is considerably thicker that that uesed in rimfire cartridges.

Whoops! sorry, my mistake! The .22 Hornet is centerfire, but the .22 Winchester Mag is rimfire.

Padeye
10-06-2000, 04:13 PM
Rimfire was around before centerfire was ever invented. The first Smith and Wesson catridge revolvers, made after Colt's bored through cylinder patent ran out, were in .22 short, a caliber that is still available. There were some larger rimfire calibers available for the .41 cal Remington derringer, the .44 Henry rifle and 5mm Remington rifle but they are obsolete.

Rimfire is cost effective to manufacture and capable of outstanding accuracy but isn't suitable for large, high pressure cartridges. Centerfire cases are made of much thicker brass near the base and rim, something not possible in a rimfire design which is a thin, uniform thickness throughout.

Padeye
10-06-2000, 04:17 PM
Originally posted by mrblue92
ISTR the .22 generates close to same pressure (18,000-20,000 psi) as many rifles.


That's the low end of the scale as centerfire goes, in the territory of light .45 ACP target loads. 9mm Parabellum is typically half again as much and rifle rounds are 2-3 times as much.

In the early days even centerfire rounds like .45 Colt were designed with a ballon head case with a hollow rim much like a rimfire. When smokeless powder came along that had to be abandoned.

Boris B
10-06-2000, 04:38 PM
Well, y'all have done an admirable job explaining this one. I have a little to add:

Though currently-manufactured rimfires are much smaller than most centerfires, the smallest cartridge I've ever heard of is a centerfire. It's the 2.7mm Kolibri, and Austrian invention for use in indoor target shooting. I'd love to see one of these up close - can you imagine how small the primer would be? And could you reload it, or would you have to take it down to the Swiss watchmaker's? I don't know. In any case, its muzzle energy is about 3 foot pounds, less than a tenth that of the weakest rimfire. The Kolibris were not cost-effective and are only found in collections nowadays.

I've always been a little bit uncertain about the advantages of rimfire. Obviously, new rimfire ammo is cheaper than centerfire, while reloaded centerfire ammo is quite economical. But what about accuracy? Some of the most accurate weapons in the world are rimfires - maybe all of the most accurate. (Although you'd be comparing apples and oranges to say that an Anschutz .22 shot better at 50 meters than an H&K or something at 500 meters.) Where do rimfires get their accuracy? I don't know if it's an inherent property of the cartridge, or if it's just really expensive to make a weapon both precise and strong enough to take the whack of a big centerfire. Another reason might be, the most accurate weapons in the world are going to be match weapons, and many matches have no minimum power requirement, so the people competing choose the softest-shooting weapons possible.

Sofa King
10-06-2000, 04:59 PM
Boris, you may be interested to know that the American History Museum of the Smithsonian has on display an enormous collection of miniature firearms. Many of them are of the belt-buckle Derringer sort, but some are miniature reproductions of rifles and such.

All of them are working firearms.

I have in my personal collection a couple of .52 Sharps rimfire cartriges used near Gettysburg. The hammer marks on them look like they were made with a screwdriver!

Padeye
10-06-2000, 07:25 PM
Boris - I just started shooting rimfire benchrest so I'm learning a lot about accuracy. I'd say centerfire has more potential accuracy, when ranges are put into scale, i.e. a 1/4" group at 50 yards compares to 1" at 200 yards but that comes with a lot of ifs.

The discipline I shoot in, ARA, uses a 1/2" diameter circle for maximum points and scores "worst edge." That means that if any part of the bullet hole is out of the circle, score goes from 100 to 50. In effect the center of the bullet hole must be limitd to a circle about .28" in diameter. Glue 25 aspirin tablets to a cardboard and hit all of them from half a football field away.

In perfect conditions there are rifles that could do that if clamped to a vise. Conditions are never perfect. A 3mph wind can knock the bullet out of the 100 point circle. Shooters use two or three wind flags between the bench and the target to read wind conditions. Reading the wind flags and knowing the non-intuitive ways it makes a spinning bullet react are the keys to winning. There are other things like properly fouling the barrel. A clean, cold barrel won't be quite as accurate as it can be until a dozen or so rounds have been fired. My ammo isn't cheap either. I use British made Eley BR-50 at $8.50 per box of 50 and there are more expensive types available. In the ARA no one has ever gotten a perfect 2500 in competition but there was a recent 2400.

FWIW I shoot an Anschütz rifle. :D A 64MP-R with a 24X Weaver varmint scope. Mine is the cheapest rifle on the line. $2-3K custrom rifles with thousand dollar rests are not uncommon.

Boris B
10-06-2000, 11:30 PM
Twenty-four power! Yow! I saw a 36X mentioned on a price list once. I knew people used them in varmint hunting, which must be quite a trial if the critters move around a lot (although at 24 and 36X ranges, I guess it's always a trial). I didn't know they were used in competition. What do you think of Weaver?

What does ARA stand for? I don't know much about competition shooting - most of the games I know of only allow iron sights.