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fs2000 front grip: I should take some pictures of where this installs. Technically it'd be very easy to install - when you field strip the FS2000, the front handguard section pops right out so that you can install forward grips, grenade launchers, tactical lights, etc. I also need to review 922(r) to see if this would be allowable...
Brief Answers
how to convert a ps90 magazine: The 30rd mag is the same as the 50rd mag, except that there's a spacer inside which prevents the follower from moving down past the 30rd position. You can cut the spacer down to allow full travel within the magazine. This is not true for the 10rd mag; there's some epoxy which is meant to prevent the mag from being disassembled.
raa saiga shotguns in calif: Cold War Shooters now sells Saiga shotguns, pre-configured with a bullet button style magazine lock.
can you leave bullets in a hot car: Absolutely yes. Unless your definition of "hot" actually involves the car being on fire, the bullets will not 'cook off'. The only consideration here would be, if you're planning to leave them in the car for defensive purposes, that you should shoot the bullets once or twice a year and replace them with new ones to ensure that the powder doesn't begin to break down from the heat. Other than this, an occasional stop in a car really isn't going to hurt your ammunition any.
is it legal to have a pistol grip on an m1 carbine in ca: Not unless you've locked the magazine in place or disabled the gas operating system so that it's no longer semi-automatic. If you've locked the mag, pistol grips are perfectly legal.
how to apply for a gun permit in california: As restrictive as California law is, there are no "gun permits" like the ones in Illinois or New York City. There is an HSC card, which is required only for purchase of handguns, not for possession.
ar-10 rifles legal for cal: Yes, there are two types of AR-10 compatible receivers which are not banned by make and model. One is by Aero Precision, and the other is by Noveske. Both are functionally identical to the banned Armalite AR-10 receivers.
dpms lr-308 california legal: DPMS's LR-308 rifles are, unfortunately, still stamped "Panther", which is listed. However, Fulton Armory's receivers (stamped "US Rifle") are off-list versions of the DPMS receiver. So - the LR-308 rifle is not California-legal, but you can substitute a Fulton receiver for the DPMS receiver and have an identical rifle.
9mm ar 15 lower receiver print: 9mm AR-15 receivers are the same as 223 AR receivers, with the exception of an installed magazine adapter. These adapters are typically designed to be very difficult to remove (so they don't fall out accidentally), but by no means are 9mm receivers different at the core.
how old do you have to be to buy a pistol in california: 21 to buy it yourself. 18 to receive it as a gift from a parent or grandparent.
are pistol caliber carbines ca legal: There's no legal distinction between long guns based upon their caliber, unless it happens to be 50 BMG. 50 BMG is the only case where a rifle's caliber changes the legality of a rifle in California. Of course, calibers larger than 50 BMG (such as 20mm, etc) are federally regulated.
Questions to Answer
california state law allows armored car to drive with a loaded gun: Pretty sure this is the case, but must make sure.