Okay, so I wanted to be sure I understand this feat correctly. Say you're using a class Hit Die smaller than a D10, and you have a +5 Con modifier. Per Durable's wording:

"When you roll a Hit Die to regain hit points, the minimum number of hit points you regain from the roll equals twice your Constitution modifier (minimum of 2)."

Does this mean that even if your hit die is a 6, you'd heal 10 for the die roll plus 5 for the usual con modifier healing for a total of 15?

No, the minimum includes what you gain from your constitution. If your hit die is a d6 and you have a +5 Con, the minimum amount of hit points you could gain from a roll is 10. So effectively, any roll on the hit die other than a 6 gives you 10 hit points.

In essence, Durable shortens the range of your Hit Die to the upper end so if you roll poorly, you still end up with a higher amount. You have a d6 for hit die, your con modifier is +5. Under normal circumstances your range would be 6 (1+5) to 11 (6+5). Durable turns that range into 10 (5 doubled) to 11 (6+5). If say you had the all mighty d12, normal range would be 6 (1+5) to 17 (12+5). Durable makes that, again, a range of 10 (5 doubled) to 17 (12+5).

It's basically to give you a safety net so when you roll a hit die it is not giving a subpar amount.

See, that's exactly what I thought the balanced version would be. But it's not worded that way, it just says "the roll", not "the roll plus your modifier". So it was just confusion once again due to the eternal enemy of RAW vs RAI.

It's...a poorly worded feat which is why it's one that people are uncertain about/avoid. The best way to look at it is sort of like a Rogue's Reliable Talent feature in which they, the Rogue, cannot roll less than a 10 for skill checks they are proficient in. The only difference is that still permits them to add their modifier on top of the d20 roll.

Durable just gives you that net to shorten the range of what you end up with when spending hit dice so what you spend becomes better and better. It obviously better rewards those with decent Con modifiers versus those that ignored their Con.

Quote from Dawodakida >>

See, that's exactly what I thought the balanced version would be. But it's not worded that way, it just says "the roll", not "the roll plus your modifier". So it was just confusion once again due to the eternal enemy of RAW vs RAI.

 Yes. It could be read either way.

However, "When you roll a Hit Die to regain hit points, the minimum number of hit points you regain from the roll equals twice your Constitution modifier (minimum of 2)."

If you refer to the short rest rules:

"A character can spend one or more Hit Dice at the end of a short rest, up to the character’s maximum number of Hit Dice, which is equal to the character’s level. For each Hit Die spent in this way, the player rolls the die and adds the character’s Constitution modifier to it. The character regains hit points equal to the total (minimum of 0). The player can decide to spend an additional Hit Die after each roll. A character regains some spent Hit Dice upon finishing a long rest, as explained below."

When you spend a Hit Die, the number of hit points restored implicitly includes your con modifier in damage healed by the Hit Die roll. So when Durable refers to "roll" in the context of Hit Die it is including both the actual die roll and the con modifier since the die roll by itself doesn't restore any hit points.

Still the Feat does not properly work on the Charsheet. Which further increases the misundersstanding of said feat 

With a 20 Con Fighter and the Durable Feat I can do a Short Rest it rolls a 3+5 and Increases my HP by 8, which is the Result of the Roll. Completely ignoring that I have said Feat which would actually force the Result of said Roll to be a minimum of 10.

To me, it doesn't feel like this one should be very confusing.  The "roll" often refers to the total including all modifiers.  It's written this way pretty consistently throughout the rules of the game.  For example:

Attack Rolls

When you make an attack, your attack roll determines whether the attack hits or misses. To make an attack roll, roll a d20 and add the appropriate modifiers.

The concept above is just called an "attack roll".  It's not called an "attack roll plus your modifiers" or even an "attack roll total".  It's just called an "attack roll".  Same thing here with the hit dice healing.

Quote from HaraiseTenshi >>

Still the Feat does not properly work on the Charsheet. Which further increases the misundersstanding of said feat 

 

With a 20 Con Fighter and the Durable Feat I can do a Short Rest it rolls a 3+5 and Increases my HP by 8, which is the Result of the Roll. Completely ignoring that I have said Feat which would actually force the Result of said Roll to be a minimum of 10.

 You are right. The feature does not work when rolling hit dice in the character sheet. However, if you look at the Features and Traits section of the character sheet, scroll down to the bottom where it lists your feats, the description of the Durable feat will state correctly that the minimum number of hit points received is 2 x your con modifier. It just doesn't seem to actually do that when rolling dice.

A Hit Dice roll is your HD + CON modifier.

What if you have a d6 hit die and a +7 con modifier?

The normal maximum is 13 and the new minimum is 14.  Does that mean that you get more than the full hit die amount or less than the minimum feat amount?

Quote from Flying_Dominion>>

What if you have a d6 hit die and a +7 con modifier?

The normal maximum is 13 and the new minimum is 14.  Does that mean that you get more than the full hit die amount or less than the minimum feat amount?

If you have a d6 hit die and a +7 con modifier, then you a) are a beefed out Wizard and b) the minimum amount of hp that you could restore when rolling a hit die would be 14, which means no matter what you roll on the d6 it will be raised to the minimum of 14.

X = 1d? + Con Mod

If X is less than 2x Con Mod then heal 2x Con Mod, if not then heal X.