I am trying to change the hand guard of my M400. I have done my research, I thought, and am in the process of stripping my barrel to install a free floating hand guard. I have removed the gas tube roll pin and both holding pins from the block. The block will not budge. I have tried using an open end wrench to twist it. I have tried to tap it loose with a large punch and hammer and I have gently heated the block all with no affect. Can anyone help me with an approach that may work?

Ill offer some advice. I am familiar with the standard and basic AR system. I've never had any of the SIG pattern AR's and don't know what differences there may be between them and standard AR's.

I would recommend you put the barrel in the freezer if you can fit it. A penetrant will also help. If you haven't already, try tapping with the punch on the gas block and knock it toward the muzzle end instead of twisting it or knocking side to side. A commercial "freeze-off" product might work for you if you can find it.

Of course, I would be conservative in this approach in the event that SIG uses some other not-so-common method of attaching the block or uses a locker or sealant.

As you posted, should be two pins(tapered or straight) and the gas block pin only. If these don't work and you don't want to pay a smith to fix it-there are numerous FF HG's that don't require removal of the gas block.

Guess I'll do a little research. I'm curious myself.

Looks like a large hammer and 2x4.

You might try Kroil...that stuff will work into some tight spaces...it might be worth a try...

Oh...and welcome to the forum

Then there is this YouTube video...




Link to original video: https://youtu.be/8RFE7BjaLuI

Thank you! The video was what I needed! I used a floor jack and the bottom of my wood vice, a makeshift press. I knew this would be the place to learn what I needed.

Thanks again!