Choosing rifled shotgun barell length

[olegburn]

Does anyone has links or refferences,articles on choosing rifled shotgun barell length?
I saw H&R Ultra Slug Hunter Compact in 20 ga for $225.00 and thought it might be nice handy sluggun.
www.hr1871.com/Images/photo_slughunter_youth.jpg
It has 22" heavy barell and trigger felt pretty good despite hearing their triggers are heavy... .
Their adult models have 24" bbl but Compact model felt so much nicer.
I don't know much about these and hunted with smoothbores few times before but switched to Savage for better accuracy and range.
Now I'm hearing the saboted slugs have started catching up and I started looking some.
My question is this: .22lr I hear has optimal bbl length of 16-17 inches,past that it is just extra weight,do shotgun have any kind of formulas?
Any info be appreciated!
During shotgun season in the woods I can picture this shotgun with 2.5x scope being nice set-up. Ranges less than a 100.
olegburn

[12ptdroptine]

I have the 20ga ultra with a Nikon Omega standard reticle scope on it. Today was my first outing with it. So far the best load is the 5/8 lightfield's.They shot a 2 hole, three shot group today at 100yds with a spread less than an inch.