Learn't a trick many years ago from a friend who was as anal on shotgun patterns as I am. It might help you guys with them sillydneder bores, wont cost more than a dollar or so to do and you'll have enough material to do several guns.
Go down to the hardward store and buy a sheet of 220 grit wet and dry sandin' paper, the stuff with the black grit. Take a bit of it and roll it round yer finger a time or two and insert it in the barrel. (If I have to tell you to unload the durn thing yer just plain dumb.
) Now roll that round and round a couple of times about 1/2 to 3/4 inches back and get a good scratch ring in there. That keeps the wad from ramming the back of the shot column because the wad slows down just a hair. The usable pattern will not change, but the worthless ones that fly way to the side will be decressed some. I wouldn't own a shotgun with out this.
Not a CAS gun, but my beloved and well worn 870 28 ga with the 0.005 restriction in the barrel started making patterns worth sendin' home for ma to hang on the icebox. With 7/8 oz hard #7 shot , (no I did not forget the 1/2) it will drop a Chinese Chicken stone cold dead at 35 yards if you do your part. There is no denser center, it is even clear to the edge and seldom even one flyer.
Never tried it, but that pop gun would most likey take any yer knockdowns down cold.
Myself if I owned a sillydender gun I'd take it to a shotgun plumber and ask for 0.005 to 0.0010 jug choking. If he asked what is jug chocking I'd say sorry, I was lookin' fer the gunsmith and go elsewhere. The cost should be far less than them screw in devices invented by the devil and much harder to foul up. Fact is I've known folks with access to a barrel mike doing it with a brake cyinder hone in their garage, The Ruskie use an impoved version on thier Olymic guns.
I have some ideas on getting tighter patterns out of a straight cylinder gun. I don't own one right now and with my recent medial problems I won't be buying one for a while, but if anyone in the area has a old 12 gauge single shot with out a choke or one they would be willing to whack to choke off of for science and would loan to me for a while I would be glad to conduct some spearments. I think it would be possible for one to get close to a modified pattern out of one with black, it is possible with nitro powder. Just some food for thought. I'll be at the NCOWS Conv. but only on Sunday. There are many ways to tighten patterns with load development. I have 25 years of notes on it, but they use nitro powder.
One thought, since plastic wads have problems, what would happen if one made up some semi-heavy shot containers out of heavy rag paper, the English did it in the muzzle-loading era, plus some that were even more complex. They bedded shot with bone meal, today the plastic sawdust is used with nitro. Perhaps grits or cornmeal, bedded loads shoot so much better, I have used them in hunting loads since the late 70's. Also high antimony shot does not distort going down the bore and most is rounder out of the bag. Round shot flies truer and less goes to the side where it is worthless.
If anyone is interest let me know. I'm just anal enough about patterns to give it a good try.
With nitro powder, patterns are improved by using the slowest powder possible to get the job done, the slower push upon ignition does not damage the back of the shot column as much, most flyers, given round shot and less barrel scrubbing come out of the back. Would Fg powder do better?