Doc hasn't chimed in yet on 410, so I'll regurgitate what I think I know without any supporting evidence:
410 slugs out of a shotgun are in the same ballistic range as a 357 Magnum handgun (on the high end, like Buffalo Bore loads), and fragment badly upon impact leading to low penetration.
Maybe that's a product of soft lead and a quality slug design could fix it, but even if it had harder lead you're still using a longarm to throw 90-110gr slugs downrange with the power of a hot 357 handgun. Smoke'em if ya got'em, but if buying new you might as well just buy a pistol caliber carbine instead or get a real shotgun.
"Are you ready? Okay. Let's roll."- Last words of Todd Beamer
One of thos eFYI things: Gila May-Hayes, out at the Firearms Academy of Seattle, has been teaching shotgunning for over a decade using the 20 gauge. She might be a really good source of info on the topic.
"PLAN FOR YOUR TRAINING TO BE A REFLECTION OF REAL LIFE INSTEAD OF HOPING THAT REAL LIFE WILL BE A REFLECTION OF YOUR TRAINING!"
I missed this thread the first time around, so I will say this for Tam and the others that that talked about female shooters. I taught female agents Shot gun, Rifle and Pistol for a few years, and the one thing that I learned is that rifle and shotgun fit is very very important. Female agents were really bruised by using full size stocks.
They were unable to get the butt of the gun into the shoulder properly and the pain off shooting like that caused most to be afraid of the gun.
I don,t know if a youth stock would fit a mature female or not, however I would suggest that you have someone that knows what they are doing fit you for length of pull and pitch. both of which can be adjusted by fitting a recoil pad.
I am kind of late on this, but wife has no use for a 12 gauge 870, and it has nothing to do with recoil. It is the weight of the 12 gauge 870, and her ability to hold the shotgun easily with one hand doing manipulations like loading, one hand shooting, etc. We set up a youth model 20 gauge 870 for her with Brockman aperture sights, a short LOP, etc. and she loves it (well as much as she loves any shotgun as she prefers a 45-70 lever gun, bolt or AR) since she can run it with one hand on account of the lighter weight. She has bird shot and buck, but her go to load is a Brenneke slug. I think the difference in terminal performance between the Brenneke 12 and 20 gauge slugs falls into the category of inconsequential increments.
I have a really-IBO that has trouble with my 10 year old's SG stock. It's a frustrating process.
I run a youth model stock on my 870. It works great to bring the action parts of the gun closer to the power area, and aides in manipulations and reloads for sure. I also shoot with my face off the receiver for both rifle and shotgun, thus eliminating any concern about getting a kiss from glass or optics.