These are impossible pictures to make much of... however because this is an interesting subject I will "guess" at the markings.
The SDP bulls-eye comes in two forms, one the a "W" in the center and the other with "Steyr" in the center, sometimes-usually both are on the barrel together, these seem to date the late 1942-early 1943 and typically in ordnance work or as sub-contracted to Gustloff Weimar (bcd) in the c-block of 1943. There is an early bnz/42 with such a barrel but it has later features that suggest extensive ordnance work. (and the bulls-eye barrels earliest appearance in bnz production is the b-block of 1942, ending mid-late 1943 numeric lots giving way to alphabetic in the k-block of 43).
In any case this is a 1942-1943 barrel, application was "probably" ordnance or as a sub-contracted barrel, you could try clear and sharp pictures to offer more clues, capturing all markings, front sight or any associated component and maybe a better guess could made, but this is not a late-war barrel.
** I have never seen a lot higher than mid-200's on a SDP made barrel (bulls-eye), so the 742 is a mystery with these pictures, maybe a rifle serial number or a waffenamt (e/749?), bcd/43's that have such barrels also carry the e/749 waffenamt.
