.50 McMillan FatMac - need Informations


I heard that the .50 McMillan FatMac was made out of a 20mm case. The primer pocket has been modified to accept a steel insert for a .50 BMG primer and had a flash tube to.

–> Which 20mm cases are used (20x102)?
–> Case dimensions , drawing would be fine
–> Picture of the Ammo/Case/Cutaway and the weapon
–> Only reloaded Ammo avaiable or factory Ammo to?

Thanks a lot, Mhistory



The 50 Fat Mac is history. The experiment never yielded the results that Gale McMillan had hoped for and it was eventually abandonded. The brass, dies, etc were sold and the new owners have yet to resurrect the idea as far as I know. Cartridge specimens are rare. Beware of fakes!

The Fat Mac is a highly modified 20mm Vulcan case. The primer is replaced with a screw-in primer pocket/flash tube unit. As far as I know, only one of the specially made receivers was chambered for the Fat Mac. It is still owned by Gale’s sons.

Here’s a photo of the one in my collection that I got from Gale hisself. The venerable 30-06 alongside. And a few other big Fifties.



Ray, would you please so kind and post a picture from the casehead - i



I’d have to get the cartridge out and set it up to be photographed in the relentless Arizona sunlight, which I will gladly do if you so ask. But here are two photos from my picture file of a 334 OKH wildcat that has the exact same treatment. Will this do?




Here 'tis.



Ray, thanks a lot for the interresting pictures, especially for the 334 OKH wildcat. I never had seen a flashtube picture from OKH before.

…whish you and yours a Happy New Year



Thought ALL the OKH rounds had the flash tube soldered to the inside of the case. Not so ?



I didn’t mean to imply that the cartridge shown was one made by O, K, or H, only that it was a 334 OKH wildcat. The Fat Mac flash tube was originally made to be a press fit but was later changed to the screw in unit which proved to be much stronger.

Charlie O’Neil’s patent for the forward ignition cartridges shows three different methods for installing the flash tube. None of the three involve soldering. (Just off the top of my head I would think soldering would be the least attractive alternative, for a lot of reasons.) A screw in tube, either by itself or a combination tube and primer pocket, is the most common and was also used by Rocky Gibbs.

While on this subject, I’m still trying to identify both the maker and user of the flash tube cases shown in the last JOURNAL.



Taking Pepper’s advice, I went back to earlier threads and found this one I missed. Just had to say, “HOW COOL IS THE 50 FATMAC” round. WOW! I never heard of that one before.


Here’s a copy of a short article I did back in 1999.


Very interesting Paul. Thank you. I really like learning about the history behind these items.


The bullet that Paul mentioned in his article is one of several that Gale tried. The one in my photograph is one that Gale made and is similar to the later Hornady A Max. None of the bullets were successful. They either came apart in flight or badly fouled the bore (or both). For his own reasons, Gale would not try moly coated bullets. He either didn’t like moly or thought that it would not work anyway. Personally, I think that by that time he had lost all patience and was ready to abandon the project. He probably knew that it wasn’t going to work, regardless, and moly would have been just one more failure.



Cool indeed! Great pictures and info.


So I take it that this would be concidered a very rare round? It is awesome! Is case hand made?


Yes, cases were hand made from brass 20mm Vulcan. Also, all dies, barrels, actions etc etc, and many of the bullets.

I suppose “rare” is relevant. Gale made many of the cases but sold the lot of them along with the dies. So in number they are probably not rare but certainly uncommon and seldom encountered. There are a few fakes floating around since anyone with a lathe can make one but without a chamber to fire-form them they almost have to be made in two pieces and glued together.



Interesting! Thanks Ron.