The ELD-X have a thinner jacket than the ELD-M. I don't remember if I took a picture of them when I cut them in half. The M's thicker jacket is to take the rpm of the fast twist barrels typically seen on match guns. I recently listened to a few podcast that Frank Green (owner of Bartlien barrels) ; George Gardner (owner of GA Precision) and Brian Litz (Applied Ballistics for Berger bullets). They talked about how the fast twist barrels would push 400,000 rpm. Also the larger the caliber the more force on the jacket and less rpm it can take. By dropping from a 7 to 8 twist drops the rpm from 400,000 to 300,000. Mr. Litz talked about many match/target bullets have the thicker jackets that a standard cup and core. Mr. Green and Gardner talked about gain twist barrels help with the rotational force applied to the jacket, keeping them together better at higher rpms. They believe that gain twist deformed the bullet less resulting better accuracy and bullets performing as intended. Mr. Litz talked about how bullet design lend to performance. I don't remember if it was a podcast or written, however Mr. Litz also hunts. And what I took from that was that bullet rpm on impact of a animal may by why we see bullet failures on game. If anyone has seen any of the videos of bullets exploding, one thing I have noticed is the distance the video talks about the bullet coming apart. A good porting is 200-400 yards. I wonder if some of the bullet failures we are seeing are bullets that are being over rotated and barely staying together and when they impact the animal they are vaporizing.
On the Berger website there is a twist rate calculator as were as the "No BS BC" there is quite a bit of written information to geek out on.
As we know many of the premium hunting bullets have thicker bullets than match/target bullets. Quite a few years ago I cut Accubonds, A-tips, Scirocco, Aframe, Partition, Core Lokt, Berger Target, Game king and Match king. The cup and core were the thinnest, match medium and premium hunting were thickest.