The bullet jacket splitting is from swelling of the tracer compound. I don’t know the scientific aspects of it, but know it does happen, as the others have said better than I. I have notice the same thing in the .45 and .30 Carbine flare cartridges made by National Fireworks Inc. during WWII - of course I imagine it takes less pressure to crack the plastic “bullet” of those rounds than to crack a GM or GMCS bullet jacket.
I am pretty sure those tracers are original and from Remington as tracers. They made the military type round (FMJ Spitzer bullet) in ball and dummy, as well as blanks that may or may not have been for the same contract. I think the tracers go right in with that grouping. I was never able to find the tracer round when they were still legal for me to have, but have seen some at Woodin Laboratory, as well as what is reported here.