I do not speak about any export problems in the US. In Germany there will be no legal problems to send it, BUT a customs/postal problem. It is impossible to send weapons parts of any kind, not only barrels, bolts etc, but also magazines, stocks etc, to any country you will need a customs declaration for, i.e. outside the EU, by normal mail with DHL, UPS or any other carrier, except a very expensive special company with special weapons permissions. I did not check it, but I do assume that this will be the case for the other way, from the US, also.