That's probably what did it. There's a federal statute mandating a 30 year sentence if guns are involved in a drug offense. The Supreme Court even ruled that the gun doesn't need to be fired to qualify.
This is what I found. The federal drug statutes include two types of commonly applied mandatory minimum sentences: drug-amount-based minimums, and recidivism-based minimums. For certain drugs in certain quantities, 21 U.S.C. §§ 841(b) and 960(b) provide minimum sentences of 5 or 10 years imprisonment. The circuits are divided over whether drug amount must be alleged in the indictment and proved to the jury to trigger these mandatory minimum sentences. For a defendant who has previously been convicted of one or more drug offenses, the statutes set out a series of minimum sentences up to life imprisonment. The prior conviction need not be alleged in the indictment or proved at trial; however, the government must follow special notice and hearing procedures prescribed in 21 U.S.C. § 851Firearms offenses. Title 18 U.S.C. § 924, which sets out the penalties for most federal firearm-possession offenses, includes two subsections that require significant minimum prison sentences. One is § 924(c), which punishes firearm possession during a drug-trafficking or violent crime. It provides graduated minimum sentences, starting at 5 years and increasing to life imprisonment, depending on the type of firearm, how it was employed, and whether the defendant has a prior § 924(c) conviction. The minimum sentence of § 924(c) may not be triggered if a greater minimum is otherwise applicable, but a sentence imposed under § 924(c) must run consecutively to any other sentence, including sentences for other § 924(c) counts charged in the same case
Source:
An Introduction to Federal Sentencing
So it is possible that he could get 28 years if he has prior convictions and the weapon in question warrants this type of minimum sentence.