Just a bit of clarification, the .38 Mk IV Webley is NOT the same gun as the .455 Mk IV Webley.
the older, larger .45 cal MkIV is a black powder (only) gun. I believe the first Webley approved (proofed) for smokeless ammo (cordite?) was the Mk V, and the Mk V was only produced for a couple years, before changing to the Mk VI.
The LATER .38s were called the Mk IV (perhaps Ruger got their penchant for confusing model names from the British???) for reasons I never understood.
"I hear these guns kick the shells out into the air if you open them. Any truth to this?"
I think it depends on the quality of the springs, which apparently varied a little bit during the war because of, well, the war.
Yes, and no.
EJECTION of the shells has nothing to do with the springs. The spring actually works the opposite way, just like the cylinder spring in DA S&Ws, and Colts, etc.
When you open a Webley, the "ejector rod" rides over a cam in the hinge, pushing it UP, lifting the shells. If things are not too worn, the shells are lifted a bit further than the length of the fired cases. At that point, empties fall out. Just past that point as you continue to open the gun, the rod rides over the lobe of the cam, and its spring snaps it back down, flush with the cylinder face, for reloading.
How "smartly" you open the gun affects whether the empties, "fly out" or not. And, of course, this applies when the gun is held level when opened. Tilt or tip in any direction aids empties, or loaded rounds falling out. You can, by holding the gun perfectly level and opening it very slowly, get a malfunction, where the cases don't (all) clear the cylinder, and loaded rounds may even drop back into the chambers when the extractor star snaps back down.
You will have to work at it, for this to happen, though.
The bulk of the .38 "Webleys" you will see are actually Enfields, though true Webleys are out there. The Enfield looks almost identical, though there are small differences.
The "official" story is that Webley couldn't supply as many as wanted, the unofficial story is that the Crown didn't want to pay Webley prices (anymore,) and had the guns built at govt arsenal(s). (Enfield)
The .38s became the issue sidearm after the first world war, but a lot of the .45s were retained, and used during WW II. From what I've read, and a couple of people I've talked to, generally the troops had greater faith and confidence in the .45 over the .38.
I know I would pick the .455 over the .38 given a choice.
Enjoy your Webley, it's a neat piece of history.