Yeah I saw that one and it shows you what's inside of the M855A1 but not the M855. The M855A1 is a bit different from an M855 round. The M855A1 has a steel tip that is inside and outside of the jacketing. Most of these cutaways show great detail of the insides of M855 but don't tell you what they materials are. Been dealing with M855 for years and never really locked into my brain what they're made of.
Here is an interesting article about the M855 round.
https://www.google.com/amp/www.thet...he-truth-about-m855-5-56-nato-ammunition/amp/