I stand corrected. Having to buy special tax stamps ($200) sounds far less burdensome than having to get a license. Good to know, and sorry I provided bad info.
Here's a good document I found on the web:
http://www.silencerresearch.com/Silencerguide.pdf with
all of the details outlined. If that document is up to date, it's legal in 34 states, and illegal in the rest. The following paragraphs is from that document:
"The following states allow civilian ownership of silencers. AL, AR, AK, AZ, CO, CT, FL, GA, ID, IN, KY, LA, ME, MD, MS, MT, NE, NV, NH, NM, NC, OH, OK, OR, PA, SC, SD, TN, TX, UT, VA, WA, WI, and WY. If your state isn’t listed here, you will not be able to own a silencer. It is my understanding that Washington State allows possession, but not the use of silencers."
State laws may add some other wrinkles, too.