475 Ackley / OKH Magnum

Looking through my junk I found what I assume to be 475 Ackley /OKH Magnum NPE made from a 375 H&H Magnum. It’s has a 4 overstamped on the 3. Is this overstamping a common thing to do and if so why go to all the trouble?


I can’t answer your question but you have a PM

Altering headstamps on wildcat cartridges is not common. Reasons for doing so range from vanity to possible liability.

What is with the neck???


Ray, they also placed a cannellure on the neck about .4" down for the case mouth.


What is the case lenght?Some say it is identical to the 470 Capstick but the bullet weight,other say it is longer.

I have asked the same question in another thread but nobody answered me…

The case length is 2.736 inches (69.5mm) Neck diameter 0.491" (12.4mm).


I think that you have a 475 Barnes supreme,not a 475 Ackley.
Case lenght match Barnes’ dimensions.The Ackley round should be longer ( more than 72 mm)

That could be. The only dimension I had were from CoTW which listed the case length for Ackley/OKH as 2.739". It also states “Both can be formed by necking up 375 H&H brass with out any other changes”. They listed the case lenght for 375 H&H as 2.85". Is the Ackley trimmed? I guess I’ll see if I can find some information some where else.


Donnely reports a case lenght of 2,85" ( from a Ackley book)

Take a look to municion.org website

Fellows, don’t forget that all of the cartridges mentioned were originally wildcats. Most still are. They were made from 375 H&H or cylindrical brass that had a nominal length of 2.85". Cases made from 375 H&H could lose considerable length in the fire-forming process and so it is not uncommon to find examples shorter than what the books say.

Bottom line - putting a label on any of those nearly identical cartridges is a crapshoot at best. Unless you had the box they came out of.



Well…straight wildcats caliber 458" or 475" are a bit difficult to identify.
I found 3 case lenghts for the 475 Ackley with differences of about 5 mm !

It’s like my 458 lott samples.The one made from 375 brass is shorter than the A-Square factory made round