"Lower"- no, no, no.
"new stripped receiver"- yes. As in a receiver, new (virgin receiver), never been built into anything or had a stock attatched. You need to document it was a stripped rec. by getting letter from factory that it was a stripped rec and never built into a rifle. But usually if you tell factory you building pistol, they frown on this. Asked one manufacturer and they said that their stripped rec. "needs to built into rifle"...and that's what they were ment for. Not going to mention who.
It can be registered as a pistol, but to built it into a pistol is a totally different subject. The AR pistols you see in shotgun news (kits) are....illegal, if it was built onto a receiver. As a parts kit, it's legal.
Feds made some evil features on pistols illegal. Look at the Professional Ordance Carbon 15 pistol. That's POST ban legal. Look at the pre ban AR pistols. Note the differences.
Post ban can not have more then two(if I get all of them) or it's called an Assult Weopon, and it's a no no
* no forward handguard
* weight less then 50 oz
* no threaded barrel or flash hider
* can't be copy of full auto version
* detachable mag outside grip
and more, but I don't have list w/ me right now
If you want a (post ban) AR pistol, the Carbon 15 and some others are the only way to go. Or go buy a pre ban for 1500-$2000. That's the going price for a Patriot pre ban.
Registering it as a pistol. Noticing you're from WA, this only applies (if I understand right) on the form that you fill out for pistols in WA (state level). The federal (yellow) form it gets listed as a part and pistol is checked. Usually it's the state that requires things to be registered if it's a pistol....that's my understanding.