I'm toying with buying an NJ compliant Ruger AR556 for use as a range toy. Within the next 2 years I'll probably be moving to America (PA specifically) and I am wondering

if the rifle can be then converted back to a normal configuration. Would it be possible and/or cost effective to thread the end of the barrel to accept a flash supressor?

I think that the pinned stock can be changed out easily, but I'm not sure if there is anything that might be a show stopper.

Any input appreciated.

Enjoy your freedom!

Honestly - just sell the upper and get what you want.  You can take off the buffer tube and change that and the stock easily.

Threading the barrel will probably cost 50-100$ then the cost of whatever muzzle device you want. You can buy a kit and do it yourself as another option. Drilling out the pin in a stock is easy.

The short answer is it probably isn't worth it.  A lot of makers for ban states don't even give adjustable stocks to be pinned.  They are bolted or glued to the buffer tube (Sig I know does this for sure) so you can't even unpin it and then make it adjustable.  You can buy a new tube cheap and stock and replace the old one.  The upper barrel can be threaded but why?

Threading the barrel will probably cost 50-100$ then the cost of whatever muzzle device you want. You can buy a kit and do it yourself as another option. Drilling out the pin in a stock is easy.

A lot of NJ compliant AR's aren't pinned they just look like adjustable stocks but aren't really.  Sig and Stag both do this.  I am not sure about Ruger.  

S&W M&P 15 and 15-22 compliant models are pinned to the full extended position and use proprietary buffer tubes/Stocks IIRC - easier just to change the entire buffer tube/stock.

A lot of NJ compliant AR's aren't pinned they just look like adjustable stocks but aren't really.  Sig and Stag both do this.  I am not sure about Ruger.  

S&W and Windham as well.....