More humor than seriousnous.. a coworker brought this up, and he's never looked at rounds before and had watch tales of the gun last night... so he asked

"why is a belted mag not considered to be a rebated rim"

I thought about this, and couldn't give him a "good answer" that he couldn't just get a pair of calipers and SHOW me the casehead is smaller than the body... at least at the belt. dang engineers

anyone care to help me explain WHY to him?

jeffe

I just measured the belt diameter and rim diameter on 7 different calibers of belted magnums.Some of them measured up to .0015 smaller on the rim,some measured up to .0015 smaller on the belt,and some measured the same on both belt and rim.Both belts and rims measured from .5245-.5315.

I measured about 25 different calibers of rimless ammo,mostly the rim was from .0015-.005 larger tham the case head although some measured the same and 2 had a rim about .0005 smaller than the head.

There seems to be quite a large manufacturing tolerance on
cartridge cases.

All of the ammo was factory loaded unfirid.

WC

Jeffe,
You can always tell an engineer ............... but you can't tell them much. And I are one.

A belted mag is not a rebated rim because the case was designed with that size rim to begin with. Generally, cases that are classified as having a rebated rim, began life as something else, then they turned down the rim to fit a smaller bolt face. Like the Remington Ultra Mags for instance. (Based on a 404 Jeff. with a rebated rim). That's my theory on it anyway.

A belted magnum is not a rebated rim because the rim is not smaller than the base of the cartridge in front of the extraction groove. The rim and the belt are "specked" at nominally the same size. Now, the case body ahead of the belt is smaller, but that makes the body "rebated", not the rim.

A true rebated case has a rim that is more than nominally smaller than the base of the case in front of the extractor groove. Examples are the .284 Winchester (rim .473, body about .500) the Ultramag, short mag, and WSM series (rim nominally .530 and case body about .550) and the .425 Westley Richards with a rim of about .470 and a case much larger (don't have the specs in front of me). There are also a couple of cartridges for automatic pistols that exhibit enough difference to be classed as rebated, the .41 Action Epress with its 9mm Luger rim and .41 body being one example.

Actually, a belted magnum case comes closer to being "classable" as a RIMMED cartridge, because a rimmed cartridge has a rim that is LARGER than the case body.

You know, a few years ago, a new shooter asked me about rebated rims and I told him not to worry about it, as he would likely never see one except as an oddity.

Now, as has been pointed out, we have the "new cartridges" coming online.

What the heck do I know?

Jeffesso,

I would tell him it was a rebated rim, but I'm a salesman that sells to Engineers.