Yesterday I was digging through some collected brass which included my stash of 1943 50 cal brass (my favorite year). I discovered a casing that is comparable to a 50 top and bottom but is 7/8 inch shorter. Any clues as to what it might be be?

With enough precise measurements, it might be possible to identify it with the charts in a Cartridges of the World book. Some pictures, including of the headstamp, might help as well.

There's the 12.7×81mm round used by the WW2-era British .50 Vickers HMG/AA guns.

Its case is 3.2 inches long, compared to .50 BMG's 3.9 inches.

Vickers 12.7x81mm on top
Browning 12.7x99mm/.50 BMG on bottom

This message has been edited. Last edited by: RogueJSK,

Thanks, we're close but the case measures 3 inches exactly. (77mm)
It's marked:
1000 - F
1400 - A
1900 - 6
1700 - 0
Suspect these are U.S. markings. The short case base is 19mm while the long case is 20mm

Sure it isn't 76mm?

At 12.7x76mm, it'd be from the M48 spotter-tracer rounds for the M8C spotting rifle mounted on a 105mm M40 recoilless rifle.

The headstamp reflect manufacture by the Frankford Arsenal in 1960, so it's definitely US, and in the right time frame for M8C use.

I think we may have a winner. It is 76mm in length. The case mouth is damaged enough to prevent accurate measure.
I have been around some 105RR firings, so that may be where it came from.