Its an SMK DB4.

I couldnt get any grouping with mine less than 3 or 4 inches, so i drowned my barrel in bisley gun oil, and cleaned it all out, and for some reason i managed to get 1 holers consistantly at 25 yards using air arms field 5.52
(i suppose it god rid of all the cheap quility storage grease.)

god knows how i did it!