Below are some measurements of D166, Sierra 174 HPBT and Bulgarian 1971. One of the five samples of Bulgarian is an odd ball - dimensionally larger and out of round compared to the rest. If have measure this stuff before and not observe this issue. Anybody shooting a lot of Milsurp knows there are the occasional rounds which take off in random directions for no reason - perhaps this is why. Otherwise, Bulgarian ammunition is very good. I have had a few FTF but always fire on the second strike and very few split cases. It is capable of 3-4 inches @ 100 consistently.
The chart is a little hard to read; looks fine until you hit save - sorry
D166 bullet diameter. Sierra 174 FMJBT Bulgarian 147 1971
sample OD (mm) OD (inch) sample OD (mm) OD (inch) sample OD (mm) OD (inch) TIR(mm) TIR(inch)
1 7.862 0.3095 1 7.911 0.3115 1 7.859 0.3094
2 7.860 0.3095 2 7.91 0.3114 2 7.863 0.3096
3 7.862 0.3095 3 7.913 0.3115 3 7.864 0.3096
4 7.856 0.3093 4 7.911 0.3115
4 7.883 0.3104 0.019 0.0075
5 7.860 0.3095 5 7.911 0.3115 5 7.858 0.3094
1 mm = 0.03937 inch
inch rounded to 4 decimal places
D166 and Milsurp.indicating micrometer set 7.850 (6.5+1.35 Grade "B" gauge blocks) (0.30955)
Sierra (and #4 Milsurp) indicating micrometer set 7.900 (6.50 + 1.40 Grade 2 gauge blocks)(0.31102)
micrometer resolution 0.001 mm.