I have a Remington 870 Tac-14 receiver I need to send out.  Have the gun stripped, but I cannot seem to get the mag tube to release.  I have taken a blow torch to where the threads would be to screw it into the receiver, but nada (this is the method to do the same with the Mossberg 590, but  it actually works).  I have YouTubed looking for an answer, but have found nothing.  All the videos I have found are covering unscrewing the cap on the front and adding an extension to the existing tube, removing it.

Ideas?

Iirc it is brazed on.

Supposedly a factory only item to work on/remove/replace

IF you did manage to get one off, you will then need an alignment jig to get it back on again
From my research into the design, it's not threaded - so removal is a case of heating to break the seal/glue/solder

Have you got the Kuhnhausen book on gunsmithing the Remington shotguns?

If it's like every other 870 mag tube then it's brazed into the receiver. Get it hot enough using an oxy-acetylene torch and it'll come out.

Some people use jigs to replace them, but I've viced them carefully, so the tube location is indexed against a front rest... Then when the new tube goes in it's resting against the same spot so you know it's aligned the same.

High-temp solder can be used for the replacement.

Shit.

Well now I know it wasn't for lack of effort.

Thanks for all the quick answer!

It's really not terrible to remove for replacement - or to braze a new one on in the case of a particular example I fixed. My "jig" ended up being a chunk of aluminum round I turned on the lathe. Took only a few minutes to whip up.

The shell stops and the ejector assembly have to be removed before heating.  The high heat will destroy the stops and ejector if left in place.  The stops and ejector are springs that don't withstand that level of heat.
The high heat also ruins the receiver finish which along with having to rivet the ejector and shell stops back in requires a refinish.

As above, the factory uses a precision alignment jig to hold the receiver and tube in perfect alignment.
If alignment is even slightly off, you may not be able to install the barrel, or off-center pressure can cause the gun to shoot off target.

At one time, Remington sold a pre-shaped piece of brazing alloy to be used to braze in a new tube.  Brownell's may still carry it.

I hear ya.  The only reason I want to do this is I am sending the receiver in for Form 1 engraving.

Yeah, nah. Just get a longer box.

Engrave the barrel, thats what I did for my SBS.

Same here.