Max - I am not quite sure what your polyethlene-filled HP bullet is. I have the SP-8 cartridge, headstamped “38 87” and the eip is similar to your bullet. I note the case that came with your bullet is dated “83” however. But, I also have a pulled bullet, complete with red case-mouth seal, and my bullet is shorter and does not have the shallow boat-tail of your bullet. Mine is flat based. Measurements as follows:
Height (Length of bullet): 0.441" (11.2 mm)
Diameter: 0.3625" (9.2 mm)
Weight: 61.5 grains (3.98 grams)
Overall cartridge weight: 118.5 grains (7.69 grams)
My round seems to match very closely the SP-8 cartridge developed for tractical groups of the KGB by TSNIITOCHMASH. However, the SP-8 is usually described as having a purple-paint bullet tip, and mine does NOT.
The SP-7 has been described to me by Russian sources as “High Velocity Cartridge, with plastic core, flat bullet meplat, violet or black tip. No hollow point is included in that description, and the “flat meplat” sounds like a flat-nose FMJ bullet to me. I have a round in my collection, headstamped “38 70” that side from having no color tip, somewhat matches the description of the SP-7. I am loathe to ull the bullet, since this appears to be a very rare cartridge. Mine has the usual red primer seal from Yuryusan, but no case mouth seal. However, neither case nor bullet show any signs of tampering. The bullet must be very light, perhaps around 55 grains (3.57 grams) because the overall cartridge weight is only 11.4 grains (7.22 grams). The bullet is GM (non-magnetic) FMJ flat point, with the sides of the bullet having a rounded ogive. The bullet measures 9.15 mm (.0.3605”) measured at the case mouth. The flat tip is 5.70 mm (0.2245") in diameter. The projectile has almost an identical shap to the cartridge we believe is the SP-8, with exposed polyethlene core. The overall cartridge length is 24.11 mm (0.2245") as close as I can measure it.
As I mentioned, this second round matchs well with the description of the SP-7 that I received, with the exception of having no tip color. It is only fair to mention here that Yuri, when I wrote him about this cartridge, had no knowledge of it and felt it might not be a factory round. I tend to disagree with that assumption. It is hard for me NOT to blieve that this round is related to the round described above, that I believe to be a form of the SP-8 round. The belief that the SP-8 rounds were evidently developed and loaded by Klimovsk on Yuryusan cases makes the headstamp dates less significant.
I would welcome any other opinions on these rounds.
To sum up Max, I am not familiar at all with the polyethrene-core bullet you have, but again, it could also be part of the development of the SP-8.