They don’t have the manpower.
We outnumber them, significantly.
All that remains is the will to resist when the time comes.
The real federal power against gun owners will be economic. Just like those who have avoided purchasing medical insurance, once the fed finds outs, it will retain your annual IRS tax refund. Now expand that strategy to what the IRS does to tax cheats - seizure of bank accounts and property. Add to that denial of Social Security and VA benefits. Few will be able to withstand that level of oppression.
Remember, 100% compliance with firearm surrender is not necessary for government tyranny to prevail.