You must blow at internetting then:

https://www.united.com/web/en-US/content/travel/baggage/sports.aspx?Mobile=1

Firearms United accepts shooting equipment as checked baggage in hard-sided shooting equipment cases.

Firearms will be accepted only from a customer who is 18 years of age or older. International firearm regulations and laws vary by destination and transiting country. Contact appropriate consulates or embassies to obtain specific entry requirements applicable to destination(s). United is not liable for any assistance or information relating to such regulations or compliance with such laws provided by any United employee or agent to any customers, or for the consequences to any customer resulting from his or her failure to comply with such regulations or laws. Firearms are not accepted to and from Bahrain, Israel, Nigeria, Philippines, Qatar, the United Arab Emirates and Vietnam. Customers traveling to Guatemala City, Guatemala (GUA) with checked firearms and/or ammunition must be in possession of a gun import license or a temporary transportation permit, which must be certified and validated by a Guatemalan Consulate. >Customers traveling with checked firearms and/or ammunition through Guatemala City do not require a permit as long as their bag does not leave the airport controlled area. Customers must ensure they have all the necessary documents required at their final destination. Customers traveling to or through Milan, Italy (MXP) or Rome, Italy (FCO) with checked firearms/ammunition are subject to police clearance at their first point of entry into Italy. Security staff will take the firearms/ammunition to the police office for inspection. Firearms and ammunition must be packed in separate containers. Customers traveling to or through Amsterdam, Netherlands (AMS) with checked firearms/ammunition must obtain permission from the Netherlands Consulate/Embassy in their country of origin prior to departure. Weapons are subject to confiscation in Amsterdam unless the owner can show all required permits. Customers traveling on military orders with checked firearms may do so without prior consent from Dutch Customs. Checked military ammunition is forbidden. For travel to and from the United Kingdom, pistols, rifles and shotguns must be packed in a hard-sided rifle case. Customers must have the appropriate license or certificate in addition to a British Visitor's Permit (BVP). A Great Britain resident will need to act as a sponsor and submit a BVP application to their local firearms licensing department on your behalf. Curbside check-in of a firearm is not permitted. Firearms must be packed in a hard-sided container with a lock. The container must be locked at the time of acceptance by United Airlines and the key or combination must remain in the customer's possession. If a hard-sided container is needed, see the container section of this site. Handguns must be packed in a hard-sided container with a lock. The container must be locked at the time of acceptance by United Airlines and the key or combination must remain in the customer’s possession. The locked hard-sized container holding the handgun may be placed inside an unlocked soft-side piece of luggage. The firearm will be transported in a section of the aircraft that is inaccessible to the customer. Proof of registration is not required. Firearms carried in addition to the free baggage allowance will be assessed at the current excess baggage charge. No more than 11 pounds of ammunition may be carried. The ammunition may be packed in the same container as the firearm or in a separate container. Ammunition must be packed in the manufacturer's original package or securely packed in fiber, wood or metal containers. The ammunition inside the container must be protected against shock and secured against movement. First or second checked bag service charges may apply.

Note: Customer must sign and date a Firearm Declaration Tag declaring that the firearm is not loaded.