I'm trying to determine if I could run a Para Ordnance Warthog in BUG-S. As far as I can tell, it meets every dimensional requirement, but has a barrel with no bushing. Does that make it a "heavy" barrel and thus excluded from BUG-S? As far as I can tell, only BUG-R has exemptions for heavy barrels.
Edit: Found my own answer. 8.2.8.2 states that ESP rules apply, and heavy barrels are allowed provided that they're shorter than 4.25". So, good to go.