Buy two Skeet choke tubes, shoot bottom barrel first.
Works for me too !
For many shooting 16 yard Trap singles, Modified or Imp. Modified seems to work out pretty well.
For Sporting, depending on the individual station layouts, Skeet and I.Cyl. or I.Cyl and Light Modified or Modified will cover most situations. A few Clubs like to feature some really long birds ... I've used Imp.Mod and occassionally even Full for some presentations (40 yards +) with 1-1/8 oz. - 7-1/2's.
I.Cyl and Modified have long been a favourite combination for many hunting situations. The range at which you expect to take your birds has much to do with choke... for grouse and woodcock for instance, I like Cyl. and Imp.Cyl., but for sharptails and Huns, I think I'd go to Mod. & Full as they're often
up well in front of the gun. Pheasant, typically I.Cyl and Mod. and for waterfowl with steel, I.Cyl. and Mod is also a pretty good choice.
You really should pattern your shotgun, initially to ensure first, if "it's shooting where you're looking" (most do this at 16 yards with either Mod. or Full) and then secondly with the specific cartridge/choke combination you intend to use at various distances. For Skeet, 21 yards works, for Trap 35 yards is favoured by quite a few, as most shooters tend to break their 16 yard targets at something between 32 and 37 yards. This same 35 yard distance is also often encountered in both hunting & Sporting Clays situations.
Forty yards with the densest portion of the pattern enclosed within a 30" circle is the standard in determining choke pattern percentage performance.
What's marked on the choke and what you actually achieve can be two different things entirely.
One degree of choke either way within reasonable range is generally neither here nor there. Select the appropriate cartridge for the clay target sport or game you intend to hunt - and focus on good shooting technique, gun fit and balance ... you'll be way ahead of agonizing over "which choke" !
