I'm not even sure if this is necessary - as I've never shot backyard clay with my new-to-me 18" 870, only done that with my uncles 28".  Mine is obviously a HD shotgun, but I want to have a little more fun than just shooting slugs and 00 buck at paper.  The barrel is tapped already, and has the Remington tactical cylinder bore choke in it.  Should I pick up new choke? Or will the distances (however far the clay can be thrown) not really require a restriction?  Or maybe a certain # shot?  Or both?  Can I get some recommendations please?  The internet is loaded with people saying "You need a 28"+ bla bla" or "I do it all the time with my 18." I'm not finding any details about if these 18" barrel guys are using a particular shot, or choke...
Again, just blasting backyard clay here.  MAYBE putting a plug in and shooting a bird, maybe.  I have no interest in trap or shotgunning at any club at this time.  Thanks!

You can never go wrong with a modified choke.

https://www.hunter-ed.com/montana/studyGuide/Shotgun-Choke-and-Shot-Pattern/201027_700048225/

Back when I shot a lot of skeet I used an O/U with Improved in the first bbl and Modified in the second.

I suggest getting both () and seeing which one works best for you.  The Mod will (should) have a tighter pattern at longer ranges.

Bust'em quick and close. My 18" cylinder barrel works fine for the backyard hand thrower occasions. If they are flying out fast and far I grab one of my longer field guns, usually modified choke

hope this helps!

would recommend a MOD choke, before I bought my Browning I was using my M4 to shoot skeet with a MOD choke

Improved Cylinder will break clays decisively out to 40 yards.  Plenty for backyard clays, and it still allow a large enough pattern for closer shots.

Thanks guys!  I'll start looking around to see what I can get my hands on.

a light modified is permanent in my 21"....

I agree with the advice above.  I have used my 20" HD with cylinder bore with good success on up close shooting.  Shooting skeet, I used a skeet choke, which is pretty open.  If you are taking long shots like trap, a modified works pretty good.

The good thing is that the Remington chokes are pretty inexpensive.  They are not hard to find used for $10 to $15.  Buy a few and see what works for you.

You're a Kurt Miller disciple aint you?

Improved Cylinder, Modified and Full have been the standards for years, they are still good enough today (and unless your clay thrower is wwwaaayyy out there I'll bet the Improved Cylinder tube will do what you need)

GunCat... yes... met Kurt around 1995 at the first or second North Carolina Tactical match I shot....

Meh - I'd just stick with the cylinder bore in there now and have fun.    

Improved cylinder is a very useful all around choke.   In my opinion modified is too tight if you just screwing around.    It's good for trap, some people use it for sporting clays.  Opinions vary.

Quoted for truth.  Improved cylinder for skeet distances.  Better yet is "skeet" choke, which is slightly more open than improved cylinder.

1 1/8 oz or 1 oz loads in #7.5 or #8 shot.  1200-1350 fps will be fine for clay targets.