I've never shot PRB's from a smoothie but have put a lot of shot downrange and there are more snake oil recipe's for patterning than there are enough guns to use them on.
Bird shot and rifles both like the smoothest bore you can get and highly polished chrome lined bores are one way to get it. I've lapped many a rifle bore both CF and ML to get rid of roughness, get rid of sharp edges on rifling, remove rust/fouling, ect. I don't really favor any one lap over another, my choice depends on what needs doing to what. I use leather, cotton, scotch pad, lead and rubber the most. Lead laps are limited to rifle/pistol bores, smooth bores I use a flexible rotary lap turning at least 650 rpm for heavy work and no less than 2200 for polishing. Combinations of lap materials can prove very effective as well, leather on each end, scotch pad to the inside and a double thick leather or single rubber in the center. The scotch pad will hold a lot of abrasive compound and as you move up and down the bore it will dispense evenly to the rubber and leather laps.
I like my compound on the thin side and prefer mixing my own starting with a base of commercial compound and modifying it to my likes. I use clover brand simply because it's what I have on hand and can get easily. I'll thin the compound with Rigid brand dark cutting oil until it gets almost runny but not quite, just about to pancake batter consistency. I wipe the bore with cutting oil prior to starting and add more oil as necessary during the lapping to keep things flowing nicely. Generally, if you're not making a mess, you're asking for problems. Gummed up laps can do way more harm than good and thus is why you need to keep the laps free of build-up to ensure even cutting at all points. Less of a concern when using a rotary lap but the practice is good to keep. When doing a rifled bore, it is critical to rotate the lap one rifling groove at least every 10 strokes to ensure even cutting. If using a non-formed lap like scotch pad or steel wool, rotate 10 degrees every 10 strokes. Lapping is not difficult but can take a good barrel that needs only a little TLC and turn it into scrap iron quickly if done wrong. Biggest thing is getting the bore clean after lapping. I prefer to shove at least one end into a bucket of #1 or #2 oil (kerosene/diesel) and scrubbing it out letting the oil wash out all the compound then follow with a de-greasing solvent (I use non-chlorinated brake clean) till you get nothing but a clean patch then just give a light coat of oil. Mineral spirits will work in a pinch too.
Jug chokes have been around for a long time and were just re-born with new names in the late 1970's or early 80's. Browning and others trying to corner the market with "super chokes" and "special trap chokes" and so on. Nothing more than what was being done 150 or more years prior to this, just given a new name and lots of advertizing. No one choke will pattern well for all shot sizes either. A rather minimal jug of .002" over bore diameter may work great for shot sizes 8&9 while a .004" will work best with 7.5 and 6. From what I've seen in practice, the more you go over the bore diameter with the jug, the better the patterns will get with larger shot out to around .009" for BB size shot. There is a lot of debate on the length the expanded section should be but most agree on 1.5 to 2 times the length of the shot charge within the bore.
I think that most pattern problems can be cured much easier by adjusting powder/shot charges and the wad column. Plastic shot cups and "pushin' cushion" wads may be easy loading and save the bore from steel shot but beyond that I think they're useless. I'll bet you dollars to dog cookies that you can take any gun with any plastic wad you want and I'll show you a better pattern with card and fiber wads. Slower loading but if you really want to dial a pattern in, it's the only way to go.
Buffer agents can also be used to provide pattern control. The buffer does two jobs, one in helping prevent pellets from deforming by squashing each other on firing and two to help keep pellets riding against the bore from imparting a spin. Commercial buffer agents (normally virgin PVC powder) can not only cost you on average 90% more than buying the same stuff from an industrial supply but usually make a considerable mess. Static electricity will have it sticking to everything except the shot pellets. While it's a little more crude and old, the flour/cornmean mixture has been proven to work and be very cheap and easy to deal with. 1 cup all purpose flour to 3 cups powdered corn meal. For the ML I pre-load film containers with shot charge and pre-measured amount of buffer, quick shake to ensure even mixture before dumping down the bore. Cartridges are somewhat easier, drop the shot as normal and then spoon some buffer on top and touch the casing to the lyman turbo cleaner to vibrate the buffer into the shot. Unless you get exceptionally tight crimps on casings, it's best to use a .025" OS card under the crimp to keep from getting pockets full buffer.
Cu and Ni plated shot will usually pattern better simply because they are harder and resist damage better. The rounder and harder the shot, the better the patterns will be. I prefer using Cu or Ni for turkeys and other tough game but regular "magnum/chilled" shot works good for everything else. Interesting fact is that using the same exact load for plated and unplated hard shot of the same size will result in no noticable pattern difference. Field experience does indicate better penetration with plated shot.
My personal feeling is that for shooting shot or bullets, you can't get a bore slick enough.
