Well I just happen to have a CSM 21 in a 20/28 gauge with 30" barrels. I also have just purchased a Fox CE made in 94 in a 20 gauge. Both are fantastic guns and I am happy with both. The 21 is my dove and clays gun and the Fox will be my upland gun.
I know a guy who just ordered a CSM 21 in 28/410 with 31" barrels and yes it will have double triggers!
Lou at CSM can do just about anything you want. One thing though, they seem to deal better on a 21 but will not budge on a Fox, beleive me I tried. Lou says it takes more hand work in the Fox.
