Jeep, all allen magnum and allen express cartridges are based on just about all you can get from a certain bullet diameter.
The 277, 7mm, allen mag and the 300 allen express are based on the 338 lapua mag.
They all get the kirby treatment, sharp shouldered, and min. body taper.
Here is a list of the parent cartridges for the different allen cartridge designs
224 Allen Magnum...........270 WSM
257 Allen Xpress...........300 Dakota
6.5mm Allen Xpress.........300 Dakota
270 Allen Xpress...........300 Dakota
257 Allen Magnum...........338 RUM
6.5mm Allen Magnum.........338 RUM
270 Allen Magnum...........7mm or 300 RUM
277 Allen Magnum...........338 Lapua
7mm Allen Magnum...........338 Lapua
300 Allen Xpress...........338 Lapua *
300 Allen Magnum...........408 Chey Tac *
338 Allen Magnum...........408 Chey Tac
375 Allen Magnum...........408 Chey Tac *
458 Allen Magnum...........408 Chey Tac *
50 Allen Tactical.........408 Chey Tac
510 Allen Magnum...........50 BMG
a pic of various cartridges with a 7mm AM 4rth from the right, its beside a 7mm STW

RR