What do you mean in terms of shape. size, colour? As I said in a previous post when CAL interviewed Dr Vanezis he suggested the marks were dark due to the fact NB was dead, or nearly dead, when they occurred.
If JB was the perp and murdered out of greed why would he hang around heating up an instrument to inflict burns? If SC was the perp why would she single NB out for such treatment?
Hot casings make perfect sense to me. We don't hear about such burns in this country as those that have access to firearms are usually well protected by clothing. The females in the clips were all wearing skimpy tops which could be considered akin to NB's pyjama top especially if his head was forward thus exposing his neck.
Casings burns don't look like the marks on Nevill. They are shaped like the casing itself and are much more superficial than Nevill's burns. The casings eject to the right which means they would be in front of Nevill's head not to the left of his body let alone to go down his shirt. This is your typical casing burn:

Sometimes the shape of the case is very well defined like this other times less well defined you just see a red mark but it doesn't burn through in the way Nevill's skin is singed this is more of a tattoo so to speak.

We know Jeremy was staging the scene. He moved Sheila and stuck the gun on her, he moved the Bible around eventually placing it in the pool of her blood. It certainly looks like his body was staged and that he didn't get in the position he died in naturally. The cushions were used to try to keep the blood flow in check. What he had in mind with the burns will go to the grave with him because no one has been able to figure out for sure what he was trying to accomplish. There is no way to get inside his head to see what his frame of reference was. Obviously whatever he was hoping to convey failed because everyone has been baffled for decades.
For all we know he erroneously thought the gun could burn flesh like that after being fired so burned him with the poker, hid the poker in the closet with the moderator and was hoping police would think she was marching him at gunpoint with the rifle in his back. When criminals have wrong ideas it often screws them but sometime police remain mystified and never figure out what the intention was.
We can guess the Bible was supposed to suggest she killed out of some crazy religious motive but why did he open it, get blood on it then close it and reopen it to the same page creating a mirror image and then stick it in the pool of blood? It would have been better by her waist because that is what someone would do if reading it then putting it down. He just associated reading with face so stuck it near her face it seems. What was with the opening and closing? Was it intentional or an accident? Who the hell knows what he was thinking for sure.