My mother-in-law had an odd assortment of guns up in the attic. When the wife bought my birthday present (SA Mil-Spec), my mother-in-law expressed surprise that I was interested in guns. Long story short, she gave me all the ones she had up in the attic.

So now I'm the proud owner of an old Winchester Model 12 in 20 ga. I have downloaded some disassembly instructions from the NRA to assist me in my new find. However, troubleshooting info is hard to find. 1911s and AR-15 I know, shotguns I'm fuzzy on. Any help would be appreciated.

When I load the tube up, the shells won't stay in the tube. The last one pops right back out. If I shake the gun a little bit, not working the action or anything, the next one will pop out as well. Any ideas on what's causing this and how to fix it? Failing that, any one know a good gunsmith in the Houston area that might be able to help? Other than that, there's nothing wrong with it that I can see aside from a bit of funk on the buttpad. I haven't fired it yet because of the feeding problem.

As a further question, is what I hear about working the slide with the trigger held back true? If so, should I be paranoid about displaying that trick in front of people lest someone think it qualifies as full-auto?

Chances are the action is full of years and years of dried up lube and probably fouling, grit, and gunk.
For some reason, many people seem to think that shotguns need NO cleaning, so they don't.

I'd guess the shell release (Winchester calls it a Cartridge cut off) is either stuck, broken, missing, bent, or otherwise fouled.

I'd start with a good cleaning and lubing.  Be sure to get all the gunk out from around the shell release.

Here's a good exploded view:
www.again.net/~steve/ipb-winchester-12.html

The Model 12 doesn't have a disconnecter, so if you hold the trigger back and pump the gun, it will fire.
This looks "COOL" but it's HARD on the gun, and you can't hit anything.
In other words, it's a range stunt that isn't good for a fine old gun.

Some of these old Winchester Model 12's are worth a fair amount of cash.  Get it fixed and don't abuse it.

That looks like the exploded view I found at the NRA. I'm using the instructions here to disassemble and I'm stumped.

Before attempting to remove the breech bolt, be sure the action slide is disengaged. Depress the rearmost arms of the breech bolt retaining lever (33) and slide the breech bolt almost all the way to its rearmost position.

How do I disengage the action slide? Or am I not interpreting this correctly? Am I supposed to depress the breech bolt retaining lever to disengage the action slide? That retaining lever ain't moving at all. I've almost reached the point where I don't want to dick with it further for fear of damaging it.

The gun is in amazingly pristine shape, given it has been sitting in an attic in Houston for the past 30 years.  There's no powder fouling or any other gunk in the gun, just a little bit of rust that shouldn't be a problem to clean up. My mother-in-law tells me her dad bought it, shot it once, and put it away.

Anyway, I think the original problem is simply a little bit of rust. The catridge cutoff should apparently swivel a bit in place, and it was stuck. If I can ever get the thing completely apart to clean it up, it should run like a champ.