The base offense level for a prohibited person in possession of a firearm is relatively low. Advisory Sentencing Guideline 2k2.1 calls for a base offense level of 14 if a person is prohibited by law from firearm possession, which along with a 3 point reduction for acceptance of responsibility yields an advisory base offense level of 11. With no criminal history (category I), that is an advisory guidelines range of 8-14 months in the federal penitentiary.
A common guidelines enhancement, however, is a 4 point enhancement for possession of the firearm “in connection” with another felony offense, which is large for an offense conduct enhancement. Courts have interpreted this enhancement very broadly, so if one were possessing felony drugs at the time of the firearm offense, or committing felony evading arrest, or committing any other felony offense in which a firearm would conceivably contribute, this enhancement applies. These 4 points alone could bump an 8-14 sentence to an 18-24 month sentence, more than doubling the lower end of the guidelines. These 4 points are even more costly for people with higher guidelines ranges.
Also, the price of poker goes up higher if you have one or two previous convictions for a “controlled substance offense” (drug delivery or possession with intent to deliver etc), or a “crime of violence” (a crime involving the use, attempted use or threatened use of physical force, or burglary of a dwelling, arson, extortion, uses explosives, or other conduct that presents serious risk of physical injury). One prior conviction for a crime of violence or controlled substance offense raises the base offense level to 20. Assuming a criminal history II category, although its likely to be III or higher, this yields a base sentencing range of 27-33 months, 30-37 months if category 3. (Assuming acceptance of responsibility points). Two prior convictions for a crime of violence and/or a controlled substance offense raises the base offense level to 24. At criminal history level III that yields a range of 46-57 months, 57-71 months for a category IV, and 70-87 months for a category V.