7mmGUY,
I don't think it's a case of shoddy workmanship, nor of either model not functioning properly. As I've speculated in previous threads, Remington may have different production standards for the various 870 models. The reported "rougher" chambers in the Expresses may be will within its specifications.
What are Remington's standards for "barrel straightness" and are they stricter of the Wingmasters? -- they don't advertise such things. If there are different standards, might not the Wingmaster slug barrels be more accurate? We expect the higher grade rifle to be more accurate, why not the same thing with slug guns?
With shotguns, "accuracy" is not as obvious as with rifles. Many people don't pattern their smooth bores. And, with the price of sabots, often a rifled bore is taken to the range for just enough shooting to verify zero. How many shooters know exactly how their favorite deer rifle will perform, but don't have a clue about their shotgun?