LEGALLY what happens when you put a stock on a pistol? ala 1911's or Glocks?

it becomes an illegal SBR unless you register it or accompany that stock with a 16"+ bbl.

ETA:  certain exceptions include C&R guns like some Lugers and BHPs.

Quoted: ETA:  certain exceptions include C&R guns like some Lugers and BHPs.

IIRC that only applies to a pistol that you purchase in that mannor, and you may never remove or modify the stock.  SKSs lose any CR status if you replace any part of them for a modern part, such as a hi-cap mag or a sport stock ect. To be C&R the rifle/pistol must remain in its orginal collectors state.

Quoted: Quoted: ETA:  certain exceptions include C&R guns like some Lugers and BHPs. IIRC that only applies to a pistol that you purchase in that mannor, and you may never remove or modify the stock.  SKSs lose any CR status if you replace any part of them for a modern part, such as a hi-cap mag or a sport stock ect. To be C&R the rifle/pistol must remain in its orginal collectors state.

I don't know about the SKS, but on the pistols you can remove the stock, if it's removeable.  The C&R pistols that can legally take a stock, like a Broomhandle Mauser for example, are perfectly legal with the stock on or off.  You can even use a reproduction stock, as long as it conforms to the original.  So while the Mauser is legal with the original-type stock, it wouldn't be legal with a stock that wouldn't be conforming to the original configuration.

There are some BHPs and Lugers that are allowed a shoulder stock as well as an Astra 400, etc.  This is due to collectability and the reason that the original configuration stock is allowed, whereas a non-original config stock is not.  

This doesn't mean that any gun that can accept a stock originally is legal.  Far from it.  My Luger has a 4" barrel, and the stock lug.  However because it is a 4" and not a Navy or Artillery Luger, legally I can't have a stock on it.  Only the Navy and Arty Lugers are allowed if I read the ATF letter correctly.

You can buy a lug for the M1911-type guns.  You may have seen them as a kit with a stock and 16" barrel.  As long as the 16" barrel is installed, you can use the stock.  If it's not, you can't use the stock legally.

For modern guns, like a Glock, etc, you need a 16" barrel, and the total length of the gun with stock has to equal the minimum required (I forgot what it is) as well.  If you use a shorter barrel, you have a SBR and it needs to be registered Class three to be legal.

While I'd admit a Stechkin would be cool, I've shot quite a few stocked handguns, and they are more trouble than they are worth.  You don't really shoot all that better with than without a stock, and carrying the stock around is cumbersome.  The reality is they aren't worth it, and that's why they died off before there were any legal ramifications about them.

Ross