Rimfire more efficient than Centerfire


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Werewolf
August 29, 2005, 10:17 AM
Went out to the range last week and spent a couple of hours with the ole 22 bolt action - mucho fun as usual.

Anyway - this morning I discovered a .22LR case in my shirt pocket that must have popped in there while I was at the range. When I looked at it I started thinking just how small that thing really is. There can't possibly be more than 2 or 3 grains of powder in there yet the 40 gr copper plated bullet in that particular brand (federal) pops out the end of a 22" barrel at 1100 fps.

Most .223 Rem loads for 40gr bullets use 18 to 24 gr of powder depending on the powder and the velocity one is trying to achieve. Velocities for a 40gr bullet run 3000 to 3400 fps depending on load.

The centerfire loads use almost 10 times as much powder in a case that's probably 5 time bigger but only get 3 to 3.5 times the velocity for the same size bullet.

Click...
Went my brain as it wondered...

Are rimfire cartridges inherently more efficient than centerfire. If the .223 was made a rimfire would it take less powder and a smaller case to get the same velocity out of it as the centerfire.

Or is it all just a function of case size and how much volume the powder takes up in it?

Inquiring minds want to know...

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Dave R
August 29, 2005, 10:35 AM
If I understand the physics of the situation...and that's a big "IF"...

Smaller cases ARE more efficient at creating velocity from a certain powder charge. To make an extreme case--if you set off a Black Cat firecracker in a warehouse, it would not raise the pressure noticeably. But if you set it off under a can, you'll shoot the can pretty high. If you set it off in an piece of 1/2" copper pipe, with a marble in there, too, you'll generate some significant velocity.

Among reloaders, its a wellknow maxim that a smaller case will give higher pressure that a bigger case, with the same powder charge. So, thicker brass=reduced case capacity=higher pressure (and higher velocity) than a thinner brass for the same cartridge. That's why some thicker military brass requires a smaller powder charge than commercial brasss.

And that's also why you have to be careful about seating bullets too deep, particularly in small cases like 9mm. If the bullet is set too deep, the case volume shrinks, and the pressure builds. Sometimes very fast.

So, yes, that small case for a .22 rimfire can make a lot of pressure with a small amount of powder.

Hmmmmm, a handloader could do an interesting experiment, and put a .22 powder charge in a .22 Hornet case, then a .223 case, and see what velocities are for the same 40 gr. bullet....

AhmuqGB
August 29, 2005, 10:38 AM
In my opinion, the heavier weight of the .223 bullets require more powder to get the velocity needed it's not an efficiency issue with the primers.

musher
August 29, 2005, 10:39 AM
Energy is mass x velocity squared
3 times the velocity is 9 times the energy in the projectile. 3.5 times the velocity is 12.25 times the energy in the projectile. Assuming projectiles of the same mass

Werewolf
August 29, 2005, 11:38 AM
In my opinion, the heavier weight of the .223 bullets require more powder to get the velocity needed it's not an efficiency issue with the primers. Bullet weight is the same. Note that I only gave data for .223 Rem and 40gr bullets same as the bullet weight in the .22LR I was firing 40gr.

In other words the the .223 and .22LR bullets under discussion are exactly the same weight.

benEzra
August 29, 2005, 11:46 AM
Musher beat me to it. To fire a bullet with 10 times the kinetic energy requires 10 times the chemical energy, i.e. 10 times the powder, since energy is conserved. Efficiency could be similar between the two cartridges.

Werewolf
August 29, 2005, 01:27 PM
^^^^^
+1

I too think musher nailed it.

MachIVshooter
August 29, 2005, 09:21 PM
.22LR case in my shirt pocket that must have popped in there while I was at the range. When I looked at it I started thinking just how small that thing really is. There can't possibly be more than 2 or 3 grains of powder in there

If you remove the bullets and weigh the charge, it is usually 1.6-1.9 grains for .22 L.R.

Jim K
August 30, 2005, 02:04 PM
It isn't that simple. The limitation on the power of a rimfire has to do with the case itself. It has to be thin and soft enough to be dented by the firing pin, yet strong enough to contain the pressure from the burning powder.

No case material that meets that criteria can contain the pressure required to obtain the high velocity of a caliber like the .223 Remington (5.56mm) or .308 Winchester (7.62 NATO). That requires a solid case head, and a primer that can ignite the powder charge without becoming a path for gas escape.

So why bother with rimfire at all? The reasons are that the cartridge is cheap and easy to produce, plus the rifles and handguns that fire it can be made at less expense. The steel does not have to be as hard, locking can be less solid, and semi-auto rifles and pistols can be made straight blowback rather than locked breech. In addition, the .22 rimfire has limited range and can be used indoors or in areas where use of a powerful center-fire round would not be appropriate. Also, the light recoil and relatively low noise of the .22 make it an ideal gun for a beginner.

Jim

JohnBT
August 30, 2005, 08:19 PM
Why bother with .22?

Because you can get a Cooper M57 Custom Classic. :D

http://www.cooperfirearms.com/custom_classic_big.jpg

Taurus 66
August 30, 2005, 11:30 PM
Let's say rimfires are inherintly more efficient than centerfire cartridges and now rimfire is universal, in a time when centerfire no longer exists. Would reseating primers be possible out of the factory?

carebear
August 30, 2005, 11:35 PM
Off the top of my head....

Assuming you could clean out the residue from the case I assume you could spin more compound into the case using a centrifuge.

Assuming you could safely buy, store and load liquid priming compound.

There'd be the risk of a dead spot if the firing pin happened to strike the already crushed part of the rim though.

:confused:

Taurus 66
August 30, 2005, 11:47 PM
Good. Then rimfires are less efficient than centerfires in regards to reloading. I think either way the primer to powder results during tests would closely parallel.

Sheldon
August 31, 2005, 02:59 AM
The 22 lr bullet is either a lead or very lightly copper plated bullet which does not take as much power to get down a barrel versus a real copper jacketed bullet.

Jim K
August 31, 2005, 11:45 AM
Rimfires are not reloadable as a practical matter. But I have reloaded them using ground up and dampened match tips (from the old strike-anywhere matches), pushing the mixture into the rim with a dental pick. It takes patience and doesn't always work. I used Bullseye powder and .22 pellets. You have to make sure that you load the case so the firing pin will not hit the old dent. And the phosphorus and ground glass in the match heads raises heck with barrels, so it would have to be a pretty dire emergency to go to that trouble.

Jim

BigG
August 31, 2005, 12:28 PM
What you are noting is the law of diminishing returns. Up to a certain point more input = more output. Past that point it provides less output for a given increase in input. Or something like that.

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