Barnes bullets are solid coppers. Copper weighs less than lead, in composite bullets.
I'll get straight to the point. Barnes 70 TSX, in 5.56. That turned into a SOF round, the "Optimized Brown TIp" round, that was deadlier than the Mk262 load, a 77 MatchKing OTM projectile.
If you compare the length of the Barnes 70TSX to the length of the 77 SMK OTM - the Barnes bullet is lighter - but longer - then the 77 SMK. Solid copper. 98% weight retention, in the TSX, which means it expands, doesn't break apart and fragment all over. Maintains it's weight, and drives through. Believe, or not believe. Maybe that was what Spomer was talking about - quote what he said, or the article he said it in.
I posted this picture here on this board on 25 Aug 2017, just to get the point across...
Here's the thread I posted that in:
You can believe, or not believe. I can explain it to you, but I can't understand it for you...