Depends on the law where you are, and whether it is legal to have a gun, and what you were doing with it. Without that information, we cannot even guess at an answer. Sort of like "what is penalty of having car?"
in MOST of the US, there is no requirement to register a gun.
I know of no gun registeration in Maryland. No such thing as a unregistered gun.
None.
There is no Federal law requiring registration of guns. MOST states also do not require it. No penalty.
As long as you legally possess the gun, none. Texas does not require registration of ordinary Title I firearms.
It can get you vioated and sent back to serve out the rest of your sentence.
PA doesn't require registration ofordinary Title I firearms, to include handguns.
Federal prison time
0 to the Death Penalty depending on circumstances
You're more likely to get shot by a gun in a state with loose gun control and without death penalty.
There is no general requirement to register guns in Virginia. Only a few states in the United States require guns to be registered; some states have made it illegal to register guns, as the United States has made it illegal to create a national gun registry.
The only form of penalty is possibly having to pay the defendant's court costs if you lose.