I own an AWC Amphibian S and without this devolving in to a "Should got a user serviceable suppressor", I'm curious as to the best available method of cleaning the baffles and the can short of sending it back to AWC.

I would take a very rough guess that this pistol has fired somewhere between 3K-4K rounds. Every shot fired has been CCI copper plated ammo. In that time I have not observed any degradation of suppression. Doesn't mean it hasn't happened, just means I haven't noticed any. It's been a great pistol and is very quiet.

For a can like this, what's the best way to remove as much funk from inside the can as possible without returning it to AWC? A soak is something for a day or two and then hit it with compressed air? An ultrasonic cleaner?

At one time, just about every can sold was sealed and non user serviceable and the world did not come off its axis. I have an original Gemtech Outback from when they were first released over a decade ago. Shot the piss out of it and then at some point paid the under $200 to have it rebuilt with the Outback II baffles and have been shooting the piss out of it since then. Rimfire does get nasty though. Not sure if the AWC is aluminum, but that would prevent use of an ultrasonic.

Gemtech and other can makers used to recommend a soak overnight in 'Ed's Red' slosh it around a bit, and then blow out with compressed air just to get the unburnt powder and crap out of it. It is not going to dissolve lead deposits though. What I did just for sh**ts and giggles, is get an accurate weight of the can (in your case the Ruger upper) and just monitor that weight to see how much crap it is "absorbing". Below are the instructions I have used for years to make Ed's Red. I just keep a tiny parts washer full of it and regularly toss any gun crap in it. Before I had the parts cleaner, I just got pipe sized to the suppressor and capped one end to soak the can.

CONTENTS: Ed's Red Bore Cleaner

1 part Dexron II, IIe or III ATF, GM Spec. D-20265 or later.
1 part Kerosene - deodorized, K1
1 part Aliphatic Mineral Spirits, Fed. Spec. TT-T-2981F, CAS
#64741-49-9, or may substitute "Stoddard Solvent", CAS #8052-41-3, or
equivalent, (aka "Varsol")
1 part Acetone, CAS #67-64-1.

(Optional up to 1 lb. of Lanolin, Anhydrous, USP per gallon, OK to
substitute Lanolin, Modified, Topical Lubricant, from the drug store)

MIXING INSTRUCTIONS FOR "ER" BORE CLEANER:

Mix outdoors, in good ventilation. Use a clean 1 gallon metal,
chemical-resistant, heavy gage PET or PVC plastic container. NFPA
approved plastic gasoline storage containers are also OK. Do NOT use
HDPE, which is permeable, because the acetone will eventually evaporate.
The acetone in ER will also attack HDPE, causing the container to
collapse, making a heck of a mess!

Add the ATF first. Use the empty container to measure the other
components, so that it is thoroughly rinsed. If you incorporate the
lanolin into the mixture, melt this carefully in a double boiler, taking
precautions against fire. Pour the melted lanolin it into a larger
container, rinsing the lanolin container with the bore cleaner mix, and
stirring until it is all dissolved.

I recommend diverting a small quantity, up to 4 ozs. per quart of the
50-50 ATF/kerosene mix for optional use as an "ER-compatible" gun oil.
This can be done without impairing the effectiveness of the remaining
mix.

Thanks for this info.

I called AWC and was told a 50/50 mix of white vinegar and hydrogen peroxide works well. A 2 hour soak followed by vigorous shaking, borebrush and compressed air will blow out a lot of goo. We'll see. They also said ultrasonic cleaning is very helpful if I have access to a machine.

Apparently they'll clean it for $90, and for $600 they will convert it to user serviceable by creating an end cap. The guy I talked to felt the round count needed to degrade suppression was 10,000+.