Scavenging shotgun shells for powder and lead is completely safe as I started it on a regular basis.
I live in an latin country in South America where powder is not legally availlable but all other reloading components yes. So scavenging is the only way there is to reload in my country.
I just recently started reloading as slowly arrives my equipment. Rigth now I am set up for 9 mm Luger but soon will be able to reload 38 spl and 357 magnum. Till now I have reloaded about 80 9 mm shells from scavenged shotshell powder.
Here is the math:
Currency= Pesos (which is any given currency unit in order to disguise/hyde my location).
1 12 ga shotshell costs 3000 Pesos. I get about 6 9mm charges from 1 12 ga shotshell brand Orbea. I use WSP (Winchester) primers and FMJ Winchester 115 grain bullets (for now. I am going to cast all bullets since it is way cheaper and lead is readily availlable). I have an S&W SD9VE 9mm pistol which cycles reliably on an powder charge of 4.3 grain (Lymans Reload Manual puts as minimal charge 4.5 grains but this shotshell powder is a little quicker burning as Unique). I have an 17 lbs Galloway spring in that pistol. 3.5 grain does not eject all cartridges. 4 grain does eject all cartridges but gives a few stove pipes. 4.4 grain cycles perfectly but as powder is rare and has to be economizised I settled on 4.3 grains. Today I shot a middle size ostrich with my 4.3 grain reloads from a distance of 110 meters on the field. I never expected to hit him but he dropped at the spot (I guess lung shot). That gives me lots of respect for the 9mm round since it seemed have passed rigth through the ostrich (although I could not find an Exit wound it had blood stream on the entrance and Exit wound, so there must be an Exit wound). To be on the safe side I contacted Nobel Sports and another shotshell manufacturer whose shotshells I scavenge and they inclusive gave me an burn rate Chart and both powders (as well those argentinian shotshells) are very Close to Unique from Alliant Powders in burn rate (they actually burn a Little quicker). So if you have Unique reload data you should be safe to use it but have to download a Little bit (allways work your loads up).
Scavenging shotshells for powder and lead is completely safe as Long as you know what you are doing and investigate lots on the Internet.
Scavenging shotshells is the only source of powder lots of People have but it is a viable and feasable source (but Labor intensive).