Understood. It's True That It Hasn't Been Officially Stated In The Manga, But I Mean, Does It Really Need To Be? This Is Madara Uchiha, A Shinobi Who's Been Alive A Lot Longer Than Sasuke, And Thus, Has Had Much More Time In Terms Of Increasing His Chakra Reserves Through Training, And Combat. In My Opinion, Some Things Can Only Be Speculated Upon, So You Can't/Shouldn't Expect Kishimoto To Elaborate On Minor Details Like This, Especially Considering The Many Inconsistencies He's Left Unchecked Throughout The Course of The Series As Of This Point In Time(i.e. How Kakashi Awakened His MS, What Exactly Happened To Orochimaru's Parents, Hashirama's Battle With Madara). In Terms Of Madara's Chakra Reserves In Comparison To Sasuke's, Just Look At His Battle With The Five Kage Soo Far; Most Of The Techniques He's Used Must Require Incredible Amounts Of Chakra, Yet He Still Remains Unfazed, And To Some Degree Even Seems To Enjoy Using Such High Level Techniques. Now, Could You Honestly Look At Sasuke's Character Currently And Say He Could Use Techniques With Similar Amounts Of Chakra Consumption Without Being Tired Out? I'm Not Saying He Doesn't Possess A Large Chakra Reserve; He Does. But It's Just Not On Par With Madara's; Not Yet Anyway.