VERY limited experience here, but directly relevant:
I just got my first one last fall - a Liberty Mystic for an 18" 357 Mag Carbine.
Having read about the "first round pop," I was worried that I'd just spent the money and was in for the wait, only to have something louder than my cat-sneeze loads.
All for naught.
Once I shot it with the loads I intended to use in it, I got no FRP. Sounds like popping a tire chuck off a compressed air hose - if that. My main/most used load is a 148 grain WC with 3.3 grains of Unique (over 2,100 loads from a pound of powder) to keep it just sub-sonic in the carbine barrel, but still be a useful load in the 3" revolvers. I've not chronographed the load in either yet, but I should be getting about 750 from the revolvers and just over 1kfps from the carbine. It's STILL a tad "too much" for close-up varmint/vermin use and will exit 'coons with enough force to put quite a gouge in the sod.
I believe that the small amount of fast(ish) pistol powder is used up way before the bullet ever clears the muzzle and there's just no fire left to consume any oxygen in the can. THAT is my GUESS, because I've never personally experienced FRP, so haven't had to experiment/deal with it to know when it will or won't happen.
I've shot some 180 and 158 grain bullets out of it at maybe 1200 fps, and I do hear the sonic crack, which is about like a 22 short in a 16" rifle barrel, noise-wise, but can't distinguish any FRP even then, but I'm still using mo more than 6 grains of Unique in that load. Haven't messed with full-house 357 Mag loads, but then the sonic crack would likely be louder at that point and FRP would be a moot point.
I let a friend shoot it in his woods a while back and he was "sawing" a small dead log in two with it (grinning like an iduit the whole time) when I suggested he put one into the wet mud bank on the other side of a nearly drained pond. We had gotten used to the "PFFU-CHUNK" sound, but when the WC hit that mud, it was LOUD, almost like someone fired a 4" 22 pistol. Left quite a hole in the mud too.