Says the published Federal Sentencing Guidelines. I don't make this stuff up, it's based on actually knowing how the criminal justice system is set up and operates.
For giggles I looked this up to today. Now keep in mind we only know part of the facts involved in determining where he falls in the sentencing guidelines, so there could be some significant departures. Also, I don't regularly calculate these things, that's something the courts do, and I have never even looked at it for this crime before, so my calculations could be off a little.
That being said:
1st, it's a crime involving a firearm as defined in 26USC5845, which makes it base level 18 points.
2nd, a guilty plea and acceptance of responsibility could get him a 2 or 3 point downward departure. However, it's likely on the advice of counsel he did everything necessary to get the 3 point departure. Putting him at 15 points.
3rd, if he has no criminal record he is 0 point, or Level I offender for sentencing.
All of that puts him at 15 points, and at the very bottom of sentencing in Zone D. Zone D is the highest sentencing category. A 15 point, Level I offender in Zone D must serve a minimum of 18 months according to the sentencing guidelines.
However, there may be facts unknown based on the news reporting that could be mitigating factors allowing for a further downward departure. If he gets a couple more points shaved off he could get into Zone C and only be looking at a minimum of 8 months. If he could get a total of 5 more points, he'd be in Zone B, and could possibly do zero time in prison.
Jail time or not, someone in this situation will serve a period of probation/supervised release.
Assuming he stays at offense level 15 he would also be looking at a fine anywhere from $4000 to $40000, and will have to pay a special assessment of $100 for the felony conviction.
Also, there are some things which could create an upward departure, but there is nothing in the story which indicates he would face any upward departure. Further, based on a recent Supreme Court ruling judges are no longer strictly bound by the sentencing guidelines, but it is rare that they don't follow them.
All of the above is the same whether the person was a cop or not.