Any advantage of Rimmed over rimless?

[ssblair]

I have several calibers, shoot a fair bit, and am well aware of the difficulties posed by rimmed cartridges when used in box magazines, but I thought that I saw an excerpt of an article somewhere once that suggested that Rimmed cartridges have an advantage over rimless cartridges in that they don't grow with reloading as much, or the brass is supposed to last longer or something.

I reload 7.62x54R and 30-40 Krag but was curious if rimmed cartridges really do have any durability advantages over rimless cases (like. 308)

Thx

 

[mac45]

Interesting......
My first impression is no. I do believe that brass stretches from just above the head of the case. This is why you can sometimes feel a small groove on the inside before a head separation.
I might be misremembering here. I'm sure someone with more experience loading for rifle will be along shortly if I am.

It would be easy enough to confirm or disprove.
There's a few cartridges that have a rimmed version. .307/.308, 8mmJ/8mmJR. Build identical loads for each, and measure.

I'm actually curious now. If anyone knows of such a test ever being done, I'd like to know about it. Not that I really see any practical use for the results, but it is interesting.

 

[karl77]

thinking of straight wall vs. tapered case. the straight wall doesn't stretch as much when fired.

the biggest deference is how the cartridge headspaces: the rimmed is off the rim and the rimless off the case mouth.

 

[billybob44]

the rimmed is off the rim and the rimless off the case mouth.

thinking of straight wall vs. tapered case. the straight wall doesn't stretch as much when fired.

the biggest deference is how the cartridge headspaces: the rimmed is off the rim and the rimless off the case mouth.

Close, but not quite.

Most/if not all BOTTLE NECK rimless loads headspace off of the case SHOULDER-not off of the case MOUTH..Bill.

Edit:I am addressing rifle loads-you may be addressing pistol loads??

 

[IndyDave1776]

As a rule rimmed cartridges go hand in hand with older, lower pressure calibers. If I were to speculate in the event that there is a difference, this would be the first place I would look.

 

[ssblair]

Well, specifically I'm looking at 7.62x54R, which I dont think anyone would call a 'slouch' of a round (or at least the Com-Bloc folks dont think so, as it is still their GP MG round).

I recognize that the rimmed cartg headspaces off of the rim, but I'm inclined to believe that as a case neck stretches towards the muzzle, eventually the shoulders are going to need to be set back otherwise the cartg will cease to fit in the chamber as the shoulder begins to interfere with the neck of the chamber. Am I right?

Might there be an advantage in that the head of the case is not "weakened" by an extractor groove? Or maybe it's just more efficient case capacity?

 

[SSGSAD]

I may be talking apples, and oranges, but .357, and .41, .44 mag all have a "groove" right above the rim. I have NOT noticed any problems, when reloading any straight walled or rimmed, weather revolver, pistol, or rifle, I load .223, and .308, as well as the 3 above... Andrew would be the ONE to talk to...

 

[45fan]

I dont reload any of the rimmed rifle rounds you speak of, but a thought that came to me, might the pressure of the round play more of a role in how quickly the case stretches, rather than the headspace method? I know the 45 colt that I reload lasts quite a bit longer than the 44 mag brass that I have, the only real difference being the 45 colt is loaded to low cowboy action velocities, and the 44 gets loaded for max velocity with much slower powders.

 

[Broom_jm]

Wow, lots going on here!

First of all, a rimmed cartridge, that also is bottle-necked, should headspace on the shoulder, not the rim. To resize the case in any other fashion would result in short case life and, possibly, reduced accuracy. Rimmed cases that are straight-walled typically headspace on the rim.

The majority of case stretching, in bottle-necked cases, occurs during the resizing operation, NOT during firing. During the firing sequence, cases expand to fill the chamber and then (mostly) spring back, allowing for easy extraction. The amount a case grows in length during this process is most often quite nominal. (They may even shrink a bit.) That is why you can frequently neck-size cases and fire them again, in that chamber...they haven't grown appreciably.

Rimmed cases are desirable in a standing breech firearm for several reasons. During the initial firing, the rim acts as positive headspace and allows the case to "fire-form" to the chamber, with minimal stretching at the web. The rim allows for positive extraction from a firearm that lacks the camming power of a bolt-action. In cold weather, the rim makes it easier to grip the rounds so loading and unloading the gun with gloves on is not as difficult.

There are plenty of very powerful, high-pressure rimmed cartridges. The rim is not a limiting factor in this respect. In fact, many of the most commonly-used dangerous game cartridges are rimmed; they are certainly not under-powered! The most powerful lever-action rounds, like the 348 Winchester and 338MX, are rimmed.

There is no strength advantage between a rimmed or rimless design and there is also no capacity advantage. The main difference has to do with feeding and extracting cases. Rimless cases feed better and rimmed cases extract better, particularly from certain action types.

 

[Iroquois]

One factor that I haven't seen in this thread is gun design. A reciever with rear lockup will actually
stretch when fired. In some cases enough to shorten brass life. The old SMLE is a good example.
A Mauser style bolt that locks up right behind the cartridge stretches less. The rimmed 303
British probably suffers from this, not sure about the 30-30, but I'd guess the same is true
for it. If you're reloading an old Krag the chamber may be wallowed out and resizing is taking a toll
on your brass. Mine was a salute rifle for years and blanks have eroded the chamber neck.