Raimey, all I know 248 was for early 7mm caliber rifles, as soon as their bore was a bit tighter, than military ones.
Later after 1912 the same caliber shown as 6,8 or 6,9 mm and it stands for plugs and again later Germans began to put on bbls the real caliber indication such as '7mm 57'
Also I never saw small bore listing for pre-1912 gauges smaller, than 172,28.
My thoughts German used indication of plugs in gauges for rifles smaller than 172,28, i.e. <.300

Geno.