Just bought a second hand Benelli 20 ga with the older Mobil type screw in chokes. Coated in black oxide. I’ve never had chokes in black oxide before.

The shotgun is in immaculate condition with virtually no exterior wear, and very little on the internals.

Except for one thing. As clean as the bore is, two of the choke tubes have thick smears of plastic inside. (The only tubes he used, I guess.) Whatever he used on the bore to clean it just wasn’t aggressive enough for the choke tubes.

I haven’t seen this kind of bad fouling on other non-coated choke tubes. Is the black oxide the likely culprit?

It's common.My Muller's do the same thing. Some WD-40 will take it right off.

Common for black oxide you mean?

WD-40 and a bronze brush does the trick on all my other shotguns but it’s heavy going this afternoon with these new to me Benelli chokes. It’s like grinding out concrete. Chukar hunting tomorrow and I want to use this choke.

Try Brake/Carb Cleaner or Acetone with a piece of brown Scotch pad.

Plastic build up is a combination of heat, plastic type, roughness of the choke and cleaning habits to varying degrees. I have some chokes that quickly dirty up to a high degree while others of the same type have not needed cleaning after years of use.

When I do clean my chokes, a couple shots of brake or carb cleaner followed by a wad of paper towel does the trick. In the rare, really bad cases a second shot of cleaner, waiting a minute, and then turning a brush with a drill has been the best means of cleaning for me. I've even heard of some scraping the inside of the choke with a pocket knife but I am not that OCD.

Many moons ago, I had a Rem 1100. When I was first stationed in the UK I ran into a fellow that had a 'Cutts Compensator-like' device on the muzzle of his 1100. I ask what it was and who made it. He told me it was a 'Pro-Point' or something like that. This muzzle device was made of stainless steel, vertically ported and was in fact somewhat oval shaped - not entirely round. He let me try the gun with the 'Pro-Point' fitted barrel. Shooting that gun was a joy. All matter of game and birds died, and clays broke. I was later given that gun and barrel (the UK imposed a magazine capacity on semi-autos and the bloke could not see 'defacing the gun' and I was about to rotate out of country and could take the gun with me), and went on to shoot 1000's of clay targets with it. It was great for skeet doubles. The 'oval-ness' apparently had an effect on lengthening the shot string and made misses into hits.

The fault with this muzzle device was that it had a propensity to 'cake' with plastic from the wads. I could tell when it was caked as it's effectiveness began to fall off. One could literally scrape layers of plastic out of the muzzle with a pocket knife. During my seond tour in the UK (same base) i ran into the bloke that gave me the barrel. I told him of my cleaning 'dilemma'. That's when he said, "You're going about all wrong mate. Petrol (gasoline) is your friend. Fill a liter jar with petrol, stick the barrel (muzzle) in the petrol and let it soak a bit and it'll clean up spotless." I took his advice. After soaking the muzzle for 30 min or so in 'petrol', I pulled the barrel out. As I'm pulling the barrel out of the 'petrol' a long 'sleeve' of plastic slid out of the barrel. That 'sleeve' of plastic was the length of the muzzle device, and as the bloke said it would be, it was spotless inside.

All this said, 'petrol' (gasoline) is a little too volatile to my liking and I wouldn't really recommend it's use on a regular basis as a gun cleaning aid. There are solvents/cleaners that are as effective and less volatile.

The gasoline trick sounds like a good one. I can easily drop the choke tubes into a closed jar.

Since posting, I cleaned the worst of them, the IC, and took it hunting on Saturday. Circumstances prevented me from checking it out on a patterning board first, but it knocked down every bird I shot at, and then the next day, with the F choke, it broke an impressive (for me) number of clays at trap.

So, I guess I'll just put up with the extra effort of cleaning them.