my first 6.5 G build, not going into battery

[grayfox]

Yes, check the mag. Particularly the front edge, if the bullet esp the case mouth, is hitting that edge then it misfeeds into the chamber. More recoil/feeding energy can overcome, but this is 1 possibility. If it is the front edge then a dremel to lower it 0.1-0.15" should do the trick.

If the spring might be too strong, then try loading up with 1 or 2 less than full load... see if any difference.