It depends on the part. Actions are not allowed in most situations. Depending on State laws, one must have a Federal Firearms License to receive guns (or actions). The BATF would be a good resource.
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Everything except a receiver/action can be mailed anywhere in the united states. State laws don't enter into it. A receiver is considered the part of the firearm that houses the trigger works (whether they are included or not) and bears the manufacturers serial number. This applies to antique firearms as well that may not have serial numbers. Contact the US postal service first, the BATF may not be the best source for mailing considerations.
If you want to Send a Frame or a Receiver go to a local gun shop and ask what they Charge to use there FFL I have a FFL and Charge $15 for a Long gun and $25 for a Pistol, all Pistols are 2 day or Overnight, by Fed ex or UPS I believe it is a Federal Law. Many States are now collecting Sales Tax on the Shipped Pistol, Rifle, Shotgun or Reciever or Frame.
Gun Parts Corp. E-Mail www.gunpartscorp.com.
You might try mail ordering parts from numrich gun parts in New York.
You can mail a BB gun via UPS.
Gun Parts Corporation is the main supplier of Numrich gun parts. On eBay, one can find Numrich gun parts. On Amazon, one can find a few Numrich gun parts.
One can get spare parts for a Nikko shotgun at some local gun retailers or through gun manufacturers. Gun parts can also be found through gun classifieds and gun auctions.
The the "Gun Parts Corporation" or Gun Broker in the parts catagories
You might try Gun parts Corp.or try the internet,gun stores in your area etc.
try numrich gun parts
Gun parts .com
Numrich gun parts can be purchased from the official 'Numrich Gun Part Corporation' website. One can purchase a number of parts including safety buttons and magazines.
An Airsoft gun
gun shop, ebay, gunpartscorp