Now that the legal niceties are explained, the reality sets in.
You can do it, but the cost of new lowers is so cheap, it's impractical.
The AR is compared to Legos, said to be modular, etc, but taking it apart and putting it all back together in another form tends to increase the wear and tear on it. I have a complete rifle - and a complete pistol. The additional cost to make one or the other complete was about the cost of the assembled lower.
In my case, about $40 for a stripped lower, and another $40 for a LPK. Add shipping.
To have gone from one to the other, add in the cost of the parts sitting around not being useful. At this point it strays into that kind of accounting we don't consider, but it's still there - we spent money on parts and if we can't use them, it's an expense.
You wind up with only one working gun. Sum total of parts is now higher - which means you really don't "save" any money. And the next issue is what happens to the parts? In most cases, we buy another lower anyway and reassemble them into their own complete gun again. Why? Because we really aren't going to swap parts back and forth to take one to the range. We would prefer to take both and have two running guns.
Guns are like that - same reason every place setting on the table at Thanksgiving has it's own knife, plus another to carve the turkey. And they aren't that interchangeable.
Just because you can doesn't mean we do, or, you should. I would press the point for a lot of shooters that if they think they can't afford another lower to finish a complete build, they aren't really prioritizing their expenses. Bring up the cost of the cell phone plan and suggest they could switch to a pay per minute and they immediately go into shock. Suggest they could defer the cost of expensive custom parts and get the commodity priced milspec ones and their fantasy is attacked. They get real defensive about the expense of freefloats and stocks - the reality being neither contribute to accuracy simply because they have the current style or are CNC'd with the Hole of the Month on them.
Been there - converted my AR from dissipator to free float with a $140 tube and guess what, no increase in incremental accuracy. It can't shoot better than the barrel, what it does it look cooler to me and I recognize that the cool factor was what I paid for.
The pistol got B5 drop in 'barrel shields' and I will contend not only shoots just as well, but cost $100 less and looks better.
There's my point - had I budgeted a mandatory part and expense into the build, it would cover the cost of a lower with LPK. Most AR builders realize that after the second or third build and the fantasy of the AR as Legos able to transform itself from one to the other becomes appreciated as that - something we talk about on the internet.
As far as the gun safe, it's just talk in the long run. Both will be sitting there eventually.
