Gunsmithing: barrel lengths and legal issues?

IT Sounds like you May "KNOW" the answer to your question...unconsciously! Most States like California require the minimum barrel length of 18 inches. You know the saying " If it is to good to be true...it Is!" Maybe (Surely) this is WHY you received a "Deal." As for the barrel. Your stuck with that one. You Would have to purchase a new (or re-built/reworked) one from a reputable gun dealer. Not...Not at a Gun Show. You could check the NRA web site for gun smiths and or the Dozens of gun magazines available. Do Not cut corners on this issue. You could have a catastrophic failure of the weapon with tragic consequences to you or anyone around you when you discharge this weapon. Additionally, depending on the state assault weapons are legal to own or Not. You did not ID your state. California, most are illegal. Some states (Kentucky) you can own just about anything short of a B52 Bomber!

If that rifle you are talking about has the flash suppressor still attached and the barrel is still within legal length I would have it heli-arc welded back up and live with it or sell it.

Others are assuming that the flash suppressor is off and the barrel is now less than legal length, but I am reading that it may be still attached. You said;..."then TRIED to remove it with a router tool" leaves doubt that the suppressor is on or off.

You currently have a gun than could get you 10 years in federal prison. You don't say what rifle it is but if you can remove the barrel I would do so and destroy it.

Make an appointment with a gunsmith to have the barrel replaced.

Having an appointment may do you some good if you get caught with it on the way because it goes to show intent at your felony trial.

Without the necessary federal permit, your rifle is currently illegal, AND was illegal to sell as anything other than a "parts" weapon.

Replace the barrel.