Here is a selection of 6x49, 6x45, 5.56 x 52, 6 x 45 Brunswick and 6 x 44 SAW case types.
The first 3 items are 6x49. These include a sectioned ball round to show the F.I.E., a NPE with scribe mark for case failure tests and a fired pressure test case which is headstamped FA 72.
The next 6 are some of the more distinctive 6x45 loadings which include a pressure test (FA 72), Aluminum alloy (FA 72), HPT (FA 73), solid steel dummy (no base hole), solid steel dummy which is lacquered and has a hole in the base, and XM733 steel cored loading (FA 73).
The 5.56x52 Special Case was made at Frandford Arsenal between March and April 1972. Reportedly only 800 cases were made and as test barrels were never received it is believed that these cases were never loaded. If seen loaded, they are often found with 5.56 mm FABRL AR-2 type projectiles.
The 6x45 Brunswick Corp. round was an unsolicited submission to FA. This round is headstamped WCC 74 556. The case is based on the 5.56x45 but is slightly longer and with a higher shoulder. They were loaded with commercial projectiles.
The final case type is the 6x44 Pre-SAW which was used at FA as a test case. It is headstamped FA 71. It is also based on the 5.56x45 case, but is slightly shorter and renecked to 6mm.