Nice gun you have there.
Mine is stock. Havent tuned it in any way.
Tested it some more over the chrony to day, and the temp was ca 22 C .
The velocity with H&N FTT was a high 638 fts, and a low 621 fts. Most of the shots (16) was aprox 627 fts.
Great guns these 850s, thats for shure