First, note that in the PRK, they've increased the minimum required length to 30" (or it's an assault weapon, regardless of other features), and in the PRK, measurements are taken with the stock FOLDED/COLLAPSED, unlike federal law, which is 26"/extended. Of course, with an AR, this is moot, because your AR is either already a PRK-registered "assault weapon", or it's already illegal.
Second, as long as you meet the length requirement, BATF/DOJ doesn't care how long your stock actually is. But HOW you make a previously collapsable stock into a non-collapsable stock IS a big deal. Basically, the only ones to win approval have the buffer sticking out to the end of the stock, regardless of where the stock is. In other words, you'd need to add material (i.e., an aluminum pipe extension) to the end of an existing buffer tube.
Note that BATF is always stricter about converting a "bad" object into a "good" object than they are about something designed totally from scratch.
Read this thread:
[url]www.ar15.com/forums/topic.html?id=56665[/url]
-Troy