I have one in SS Herman. There is some substantial blowback but it is directed out the cut for the primer carrier. Something could probably be done to minimize the blowback but it really isn't much of a problem with this design. Mine has an excellent trigger and seems to be quite accurate. Very easy to carry and use.
H&R Barrel Accessory Program will explain the situation with barrels. The Huntsman is an SB-1 action so will only accept muzzleloader and shotgun barrels (to 12 gauge). The Handi-Rifle models use the SB-2 action and can be fitted with any of the CF/BP/Shotgun (except 10 gauge I believe) for the prices listed on the link. The actions have to be returned to H&R to have barrels fitted but the pricing seems worth the wait, especially if you sent it during the off-seasons. ONE Encore barrel could easily cost the price of three barrels from H&R.
You can see no clearance in this pic betwen the scope and hammer, but there actually is a very slight amount - just barely enough. Those are Weaver Hi rings on the H&R base. The hammer is wearing the H&R hammer extension. The gap you see at the rear of the barrel is where the tab of the primer carrier protrudes and the blowback vents. Would probably be a bit more of a nuisance for a left-handed shooter.