My Colt .22 LR conversion kit has served well, running like a sewing machine atop my Springfield 1911 frame.  Until a couple of days ago, that is.  It stopped going fully into battery.

It wasn't long before I discovered the reason.  There is such a buildup of fouling that the floating chamber cannot be removed from the barrel.  You know how it's supposed to be loose enough to rotate out for removal, once you get the barrel out of the slide?  Well, it's stuck in there as if it were welded to the barrel.  So I can't even clean it.

Here's what I've tried so far:

-Left the barrel/floating chamber assembly in an ultrasonic cleaner for about an hour.
-Soaked it in Hoppe's #9 overnight.
-Soaked it in denatured alcohol for several hours.
-Attempted to twist the floating chamber free while holding the barrel still, using both fingers and heavily padded tools (so as not to mar the finish).

Nothing will budge the floating chamber.

Any ideas?

I thought about applying heat, but I'm not sure that's a good idea.  My blowtorch needs a new gas cylinder anyway.

The Williams type floating chamber is notorious for leading up.
Sometimes it does it quickly with some ammo, and sometimes it'll go a good while, but sooner of later it leads.
Best advice is to try different ammo to find one that doesn't lead as bad.  Often, the better grade copper or brass plated types lead less than the plain waxed lead bullet loads do.

Also, check the piston often to catch it starting to lead.One trick is to send the piston and barrel out and have the piston and it's seat in the barrel hard chrome plated.  This makes it easier to clean and lead sticks less to the hard chrome.
Clean with a "lead-away" cloth.

In this case, your options are:
Use copper or brass padded Vise-Grips on the chamber and the barrel in a padded vise and rotate the chamber.  This won't work well, because the piston is basically soft soldered in place.

Apply heat.  Note that .22 bullets are fairly soft lead and will usually melt at under 450 degrees.  That's not that hot.
You can dip the chamber area in a casting furnace full of lead to heat it up, or you can use a torch to apply heat.
Again, 450 is not that hot.  Don't overheat.
I'd put the middle to front of the barrel in a padded vise and heat the chamber.  When you think it's hot enough, grab quickly with padded pliers and rotate and pull.
You don't have to have it hot enough for the lead to flow, just hot enough to release.
When heating metal to solder or melt lead, most people WAY overheat.

I can't add anything to the remedy suggested above, but for the benefit of those of us who haven't (yet) had the same problem, what ammo "were" you using.  I've been using Federal HV copper washed brick ammo, without a hint of any issues, and have extended the interval between cleanings to 500 rds +, or whenever I feel like it.  Good luck and report back on the progress you're making

Ammo was a mix of CCI Mini Mag, and CCI Blazer.  Lately, I've been shooting only Blazer.

I've shot probably 500 rounds since the last cleaning, possibly more.  There was no indication of a problem until last Thursday, when it stopped working.

Ammo was a mix of CCI Mini Mag, Remington, and CCI Blazer.  Lately, I've been shooting only Blazer.

I've shot probably 500 rounds since the last cleaning, possibly more.  There was no indication of a problem until last Thursday, when it stopped working.

Wondering if you got some brass shavings jammed in between the chamber and barrel.

It's the nature of the Williams floating chamber that you can be shooting along with no trouble and it suddenly stops.
When you disassemble, it's horribly leaded, and you wonder why there was no indication of the problem before it totally leaded up.

Again, all you can do with these is experiment to find a brand/type of ammo that works better than others.  Also again, the plated more expensive ammo tends to lead less, but even some of it will fail fast.
There's no rhyme or reason to leading in these kits, so recommendations on ammo to use is nothing more than experience in one unit.  What works great in mine may lead yours up in 50 rounds.
In all cases, you have to inspect and clean more often than 500 rounds.
Once it does start to lead up, it usually leads up badly fast.
Also, you can't depend on the brand you find to work well not to suddenly lead up horribly for unknown reasons.

These Colt units are fun, reasonably accurate, and cheap shooting, but the erratic leading can make you crazy.

So, I got it fixed, finally.

As I half-expected, the floating chamber was quite literally soldered into the barrel by lead accumulation.  I stuck the barrel in a vise with a piece of leather wrapped around it, so that it wouldn't melt the padding on the vise jaws.  With careful application of a blowtorch and use of a brass punch & brass hammer, I got the chamber free.

A combination of 1500 grit sandpaper, a small screwdriver, and elbow grease cleaned up lead stuck to the floating chamber piece.  Inside the barrel piece, there was a ring of lead where the cartridge gases would normally vent, just ahead of the chamber.  After I had scraped away some of the lead, the rest fell out in one piece.  

Both barrel & floating chamber now have a nice case-hardened look to them, due to application of fire.  I don't think they are any worse for wear.

Obviously, I need to check this thing more often, perhaps every trip to the range.

Again, a great way to keep these clean is to buy a "lead-away" cloth.  These will literally wipe the leading off, but be warned they will also wipe bluing right off.

Having the piston and inside chamber area of the barrel hard chrome plated reduces leading problems and makes clean up much faster and easier.
Many of the professional platers offer small parts plating at reduced prices.

However, the best way to keep these working is careful experimentation to find a brand/type of ammo that leads less, and watch it a lot closer.

One thing about learning the hard way, you will not forget this. Glad you got it out.

FWIW I found the culprit.  Starting with a completely clean conversion kit, I fired two magazines (20 rounds) of Blazer.  Then I took apart the gun.  The floating chamber was already starting to get stuck!  When I pulled it out, there were two small lead deposits which had formed just that quickly.

So, no more Blazer could be the solution.  I suppose an Ace kit should only be fed plated .22 LR.

Plated sure helps.  Put about 100 rounds of Federal plated .22 through the Ace kit yesterday.  Took it apart afterwards.  It was dirty, but the chamber was completely free to move.

lube the floating chamber with synthetic motor oil, I use Mobil 1, but any one will do. When you clean it wipe the extension with motor oil and the chamber area of the barrel, and just before you shoot it pull the slide back slightly let the chamber slide back and put a drop of motor oil on the floating chamber. It will not stick and all the carbon and lead will wipe right off.