What is the 12.7x42mm cartridge? Is it the same as .50 Beowulf?

The short answer is that they are the same thing. The bullet’s diameter is 0.50″ which is 12.7mm and the case length is 1.65″ or 42mm. The reason you see some vendors say they have something to sell in 12.7x42mm is they are trying to avoid a trademark problem with Alexander Arms. In other words, they are the same thing and people are trying to avoid a trademark infringement lawsuit.

Bill Alexander, of Alexander Arms, did all the engineering to bring to life both the round and the AR components to use it. He trademarked the term “.50 Beowulf”. As such, anybody who wants to sell something and refers to it as being for .50 Beowulf would need to get the permission and/or license the use of “.50 Beowulf” to avoid legal problems. So, a lot of vendors use the generic metric designation of 12.7×42 to avoid legal hassles.

With that said, bear in mind that not all engineering is equal. I have never had a problem with Alexander Arms parts but myself and others have had plenty of headaches with 12.7×42 components from budget AR vendors who haven’t done the engineering so buyer beware and research a vendor and their offering before you buy plus make sure they are reputable in general in case you need support.

So, short post this time. 12.7×42 and .50 Beowulf are the same round with different descriptions. but be cautious to check out vendors selling parts using the metric designation.


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My apologies but I have no way to filter out items that the vendors have sold out such as ammo. For example, most places sell out of the ammo fast but you should keep an eye on both Midway USA and going to Underwood Ammo directly – Underwood makes very good ammo by the way. I usually run Alexander Arms ammo but they are sold out most places and while you can place an order directly, you will need to wait quite a while for it to be made and shipped.