I was attempting to remove a pinned muzzle brake off a 16" barrel and ran into a problem.  I cut the weld off with a dremel and was able to get some of the pin out, but it looks like the pin broke in half and some of it's still left inside the hole.  I tried a magnet hoping what's left of the pin would come out, but that didn't work, although it wasn't a very strong magnet.  Also put barrel in vice and tried twisting the brake back and forth hoping to break the remainder of the pin free, but no luck.  Any ideas?

The part of the pin that came out is what's above the barrel in this pic.

You are going to have to get the right sized drill bit and drill a small amount into the part still in the barrel and then basically reef the hell out of it to get it started, most of the pins I have done and have seen have been just about 1/16th of an inch, which is going to be tough, but you don't have to drill very far into the piece in the barrel.

Do not attempt to hold the upper with an upper vise block, you are going to need barrel blocks very close to the muzzle device, so you are not imparting any torque on that upper, if you have a drill press that can handle that small a bit, all the better, it can be done with a dremel and a very small carbide dremel bit as well.

Just take it very slow and realize you may have to dress the threads when you are done and before you put the new muzzle device on it.

If you are not comfortable, I would be happy to get it off for you, I have the tools to do it and I will send it back to you for just the cost of postage, then you can put your new muzzle device on it.

What brand are you dealing with, I know for a fact that some of the Bushmaster stuff has two pin and welds on them, they are a real bitch and their pins are pressed in.

More grinding.  I had one much worse than that. 

Or if really bad, click here and scroll down about 2/3 of the page.

Turn over tap fast with small hammer.
or
Drill all the way through the pin.
or
Grind all the muzzle brake off around the pin until it is not an issue.

Are you %100 certain that it's broken? That may be all that's there.
My pws brake with the flatspot used a considerably shorter pin than my a2.

Thanks all for the replies! No I'm not certain if that's all of the pin or not, which is why I'm worried about trying to drill it out further. I tried removing the brake, but I couldn't get it to turn. Although I don't have a barrel block, just an upper receiver block, so didn't want to apply too much torque and possibly damage the upper or index pin. I also tried putting barrel in vice with some plastic jaws I have, but the barrel kept turning.

Any tricks for making an easy barrel block? Could I just wrap barrel in some bike tire inner tube and put that in vice? Would that protect barrel well enough?

I also emailed ADCO, who pinned that barrel, and Steve said it looks like that's the whole pin. So it might just be that I need to secure the barrel better and apply more torque to twist brake off.

If it is an ADCO job, then you got it all and just need to be able to hold the barrel better so it does not turn.

Just curious if it is common to pin a 16" barrel.  Never heard of such a thing.

Try heating it up before attempting to loosen.

Its not too common.  Some states require it i believe due to their current gun laws, but OP is not in one of those states.  He said ADCO did it, curious as to the reason it was pinned as well

That brake was pinned because I used to live in a ban state where that was required. Now that I don't anymore no need for it to be pinned and I want to remove it as I want to change the handguard.

So I tried securing barrel in vice with bike innertube and then leather strips and it still kept rotating when I tried to remove brake. Also tried hitting top of it with hammer and using compressed air to get out anything blocking brake from turning, but no luck.

I emailed ADCO and Steve said he'd remove it for just cost of return shipping so I sent it off a few days ago. I guess it was delivered today as I just got tracking notification email from ADCO that it's already on the way back to me!

So a big +1 for Steve and ADCO...and a -1 for me at failing to get brake off myself