The chrome lining isn't necessary for "hardened" lead shot but if it's your criteria you are limited mostly to Pedersoli for a production smoothbore. You can put choke tubes in any barrel with ample muzzle thickness, even the chrome lined barrel(s). You will need to seek out a shotgunsmith that has a cutter for the chrome lined barrel(s) but there are plenty of them. How much shot do you want to use and how serious or competitive are you? I use a Pedersoli 20b (which uses 19b components) that has a Mod choke designation in the left barrel. With one to one and one sixteenth ounce of shot I can break trap targets just fine. I admit my score is just a little lower than a conventional shotgun, but not entirely due to shot/choke. The moderns are fitted a bit better, loads have slightly more consistent velocity and I do use one and one-eighth ounce loads. I'm talking 20/25 instead of 25/25. The 20 gauge is available in flintlock or percussion.
Now, with my Pedersoli 12b I have choke tubes. Forget what they say on them, I use the one that demonstrates the best pattern (on paper at 40-yards) and I use one and one-eighth ounce "hard" lead shot. I have "fit" that stock for my cast, drop and length using the 16-yard method. With this shotgun/choke selection and load I can shoot as well as my modern shotguns on trap and skeet (different chokes and loads for skeet).
If you're sticking to trap, a single barrel should serve you're need and keep the cost of choking down. Again, Pedersoli makes one in flintlock and percussion.
Nothing wrong with jug choking. It can produce the results you want. One draw-back is that you can't keep tweaking it. You can cut a jug choke and pattern. If it isn't what you want, you can cut again and pattern again. If you don't get what you want after the second cut you are going down-hill. Whatever you start with, you will still need to experiment with loads to get the pattern you want. The difference with a choke tube is that you can stick to one load and go through patterning with multiple choke constrictions. Then you can change the load if you're not satisfied and go through the tube selection again on the pattern board. There are just more combinations available changing loads and chokes than jug-choking and just changing loads.
You can try different "modern" wads that will effect your patterns. With more traditional loads you are depending on the charge/shot ratio and choke to produce the pattern. With the modern wad, you are adding another influencing variable that you can experiment with to make even more change to the pattern.
Here's an unrealistic and hard to replicate scenario just for demonstrative purposes. These are round numbers just for the example. Lets say your best trap gun has a .725 bore for 28 inches of barrel length and chokes to .700 for the last two inches. Your favorite modern ammo loaded at the factory gets X FPS at the muzzle. If you made a barrel with the same exact tube diameters at the same lengths, then took the wad and shot out of your modern cartridge and figured out how much BP to make it the exact same FPS at the muzzle - in theory you have created the same exact conditions for the wad full of shot and it should produce an almost identical pattern. Because this is far from probable, you have to compare the two patterns from the modern and ML differently. You have to shoot one pattern with the modern that you are satisfied with and then work to replicate that pattern from the ML changing one thing at a time until it happens. How it happens doesn't really matter. If the end result is a nearly identical pattern, either shotgun is providing you the external results you want.
For what you are doing, gun-fit and pattern are really important. You are not going to get the velocity or consistency (standard deviation) of premium modern ammunition from your ML. You can just about replicate the performance parameters of the classic Win AA Trap loads with your ML up to the 1200 FPS with the right components, so there is not disadvantage there. However the pattern from your ML will be greatly influenced by velocity and you may find the ML patterns best with a velocity 100-200 FPS less.
- Light Target Load: 1145 fps
- Heavy Target Load: 1165 fps
- Xtra-Lite Target Load: 1180 fps
- Heavy Target Load: 1200 fps
- Super-Handicap Heavy Target Load: 1250 fps
- Lite Handicap Target Load: 1290 fps
Pick the gun you like, get it fitted and start experimenting with BP loads before you mess with choke. If you can't reach your goal, decide jug-choke or choke tube and start experimenting with loads again until the pattern you are after is achieved.