Gunslinger full round action
I'm having trouble understanding some things when it comes to being a Musket Master and full round actions. I'm a level 7 MM, so that archetype gives me Rapid Reload at lvl 1, allowing me to reload a 2 handed firearm as if it is a 1 handed (full round action>standard action), then Fast Musket at lvl 3 allowing me to treat my musket as a one handed weapon while reloading (standard action>move action), and then if I use alchemical cartridges, that reduces the reload time again (move action>free action). As I understand, that allows me to move, shoot, and reload all within a normal turn. However, when one gets to level 6 and is able to get multiple attacks as a full round action, according to other forums a gunslinger only gets those bonuses if wielding pistols or a multi-barreled gun, but not when reloading is a free action, or with Rapid Shot or any other feat to boost fire rate, so no matter what a single barrel 2 handed firearm can only fire once per round? I understand this train of thought as a musket- or rifle-wielding gunslinger can be quite OP having to only beat a target touch AC instead of regular AC like other classes within proper range, but that's not how I've been interpreting it...
Even the deed Dead Shot uses an example of a MM using "both attacks":
Dead Shot (Ex): At 7th level, as a full-round action, the gunslinger can take careful aim and pool all of her attack potential into a single, deadly shot. When she does this, she shoots the firearm at a single target, but makes as many attack rolls as she can, based on her base attack bonus. She makes the attack rolls in order from highest bonus to lowest, as if she were making a full attack. If any of the attack rolls hit the target, the gunslinger’s single attack is considered to have hit. For each additional successful attack roll beyond the first, the gunslinger increases the damage of the shot by the base damage dice of the firearm. For instance, if a 7th-level gunslinger firing a musket hits with both attacks, she does 2d12 points of damage with the shot, instead of 1d12 points of damage, before adding any damage modifiers. Precision damage and extra damage from weapon special abilities (such as flaming) are added with damage modifiers and are not increased by this deed. If one or more rolls are critical threats, she confirms the critical once using her highest base attack bonus –5. For each critical threat beyond the first, she reduces this penalty by 1 (to a maximum of 0). The gunslinger only misfires on a dead shot if all the attack rolls are misfires. She cannot perform this deed with a blunderbuss or other scatter weapon when attacking creatures in a cone. The gunslinger must spend 1 grit point to perform this deed.
So, does the extra attack gained at lvl 6 count as an opportunity for an extra attack, or is Dead Shot illustrating the use of a pepperbox rifle or something (it would be odd that it didn't specify an important detail like that, IMO)?
Others also point out that the crit multiplier, large damage die, and ranged touch AC attacks make it too OP, but I thought other downsides were the enormous misfire range (1-4), the fact if you misfire twice (without feats to counter it) the weapon explodes, and the price of just about anything associated with firearms was pretty steep. I still understand the concept of limiting the fire rate, but are my interpretations that far off?