What is this switch on the sg12 forend?

[u/rastamasta45]

Bottom of the hand guard end of the pump handle before magazine tube extension. Spas12 clone

[u/NormalBill76]

To change the gas settings? It’s right next to the plug

[u/IAMURBUNKLE]

Silencer activation 

[u/One_Salary_9068 → u/IAMURBUNKLE]

Switch caliber 🤌🏼

[u/rastamasta45 → u/One_Salary_9068]

The mythical double shot from half life???

[u/Comfortable-Moose492]

Shoulder thing that goes up 👍 hope this helps

[u/pphresh204 → u/Comfortable-Moose492]

a barrel shroud?

[u/Oogaboooganator]

Adverse conditions/dirty setting?

[u/Mercy_Jordan]

Some of my semi auto shotguns uses a system that has selector for lighter rounds like birdshot and for heavier rounds like buckshot or slugs and magnums or what not. Take it to the range and see if it cycles properly or not.

[u/MacPapRonin]

Do you own the shotgun? If so, did it come with a manual?

I would check the manual.

If it's similar to the original Spas-12, that would be the selector between pump action and semi-automatic fire. [edit] watching a couple of videos, it seems that's probably not correct - the switch between semi and auto is a button on the bottom of the slide.

As others have guessed at - perhaps a gas system switch?

[u/rastamasta45 → u/MacPapRonin]

Checked the manual, says nothing

[u/MacPapRonin → u/rastamasta45]

Are there by any chance markings on one side vs. the other, perhaps S on one side and M on the other, or something similar?

Perhaps with snap cap shell in the chamber and a couple in the tube, try manually cycling the pump, pulling the trigger, then repeating, and seeing if you can work the pump action with the switch on one side vs. the other?

[u/Xaxxus → u/MacPapRonin]

The manual for this gun is probably about as useful as guessing what these things do on your own. One of the worst manuals I’ve ever read

[u/Opening_Pizza]

This guy switches it to the left for disassembly. But he doesnt mention it.... https://www.youtube.com/watch?v=soQD_8ZG6vI

[u/613mitch]

It switches the action from pump to semi. Look at the handguard and youll see a path that activates the switch when you switch modes.

[u/King_Merovingian]

Secret hidden giggle switch. Play with it and giggle. 🤭

[u/ceaddl]

On the sg-12 this is the gas valve, when you lock it into semi auto this valve gets moved into position, when you switch to pump the valve is disengaged and closes. You can see this if you flip the gin over and look in there as you lock it into semi.

[u/mywaaaaife]

Full auto

[u/-based-bot-]

It’s the flux capacitor switch

[u/Agent_1812]

Fully semi auto

[u/Danlabss]

Bump stock 3 million rounds per minute button

[u/Ustauk]

Here's what the Google Gemini Large Language Learning Model said when I asked your question:

"On the Sulun Arms SPAS-12 clone (often sold as the SG-12 or SPASS-12), the switch or button located at the bottom of the handguard/forend right before the magazine tube extension functions as the forend/slide release (or action lock release).

Here is what it does and why it is there:

• Unlocking the Action: Unlike a standard pump-action shotgun where you pull the slide back after firing, a dual-mode hybrid shotgun locks the action closed when a round is chambered in semi-automatic mode (or when the gun is in battery) to ensure proper gas operation.
• Clearing the Chamber Safely: If you have a live round in the chamber and the magazine tube, and you want to unload the shotgun without firing it, pulling back on the pump handle won't work immediately because the action is locked. Depressing that specific button on the bottom of the handguard disengages this lock, allowing you to manually rack the slide rearward to clear the chamber.

(Note: On the original Franchi SPAS-12, a similar lever/button sits underneath the forend to let you selectively isolate or hold back the feed mechanism or unlock the slide depending on the context of clearing/loading)."