This is a list of search terms which I believe deserve answers (or better answers than they received when the user clicked on them). I'll be undertaking this endeavor soon. There may be a few other questions added as well; this contains the results of analyzing the search terms for October.
replacing sks pinned barrel: Unfortunately, any replacement barrel for an SKS would have to be turned from a blank and more or less made from scratch. The issue here is that not only are replacement barrels unavailable, but that a lot of effort would be necessary to change a barrel from being a blank, into being an actual SKS barrel.
legally acquire threaded handgun barrel in california: Just like a pistol grip for a rifle, you may own the part all you want. However, it is a felony to install it on your pistol, unless a 10rd magazine is fixed in place.
install a off list lower on your ak-47: If you have a listed receiver, you could indeed cut it, remove the parts from it, and rebuild the rifle with an off-list receiver. That having been said, it will require considerable metal work and is not for the faint of heart.
primer size for .223/5.56 rifle: All the Boxer-primed brass I've seen has used small rifle primers. There's some Berdan out there, though.
how many handguns can be legally transported into california: There is no limit, however you must register all handguns that you transport in when moving into the state. See LegalCaliforniaMovingTo.
convert automatic ps90: No, this is never going to be answered.
bushmaster m17s california illegal: Sadly, yes. It's a real pity, because I've wanted one myself for some time.
ar 5.7 rifles conversions: Rhineland Arms AR-57.
batf 922(r) saiga 7.62: The Saiga is entirely made from imported parts. It is not necessary to alter one to be 922(r) compliant, unless you're modifying the rifle from its original imported configuration. If this is what you're up to, I recommend using the AK-47 922(r) checklist. You won't have to count the pistol grip as an imported part, because this is not a part of Saiga rifles.
california handguns magazine outside pistol grip: If it's detachable, this is a felony in California. A fixed magazine, such as a locked AK pistol mag or a Mauser pistol's internal magazine, is allowable.
removing a pinned and welded flash suppressor: To do so, you'd have to drill or punch out the pin, and cut the weld off using either a dremel or other tool. Breaking welds is, by its very nature, guaranteed to cut into the original barrel. It's also necessary to ensure that your desired result is actually legal in your state and country. Pinned and welded flash hiders are usually used to bring rifles up to 26" overall length, or barrels up to 16", when otherwise too short by federal law.