5-IN-51 Cal MK3 Catapult

I was recently given 2 casings from WWII. A 3 inch and a 5 Inch. I am interested in finding out about the 5 inch 51 cal. How it was used and how common is it. The full stamping on the base is 5-IN-51 CAL MK3 CATAPULT N.S -3-1942 - JCA (US anchor symbol) Lot 49.
The primer has been removed but I do have the cork cap. I’ll upload some photos as soon as I can



Welcome to the forum.

The basics: 5” 51 cal. case length is 33” & rim diameter is 7.4”, designated the 5” MK 3 cartridge case, for the Navy 5"/51 caliber gun (barrel length is 51 x 5" = 255 inches).
What is the length of your cartridge case?
With the “catapult” designation in the headstamp, the case was possibly repurposed to be used in catapult launching of seaplanes off of Navy ships.


Thanks for the replay, The rim is 7.4 and length is 33 inches. The top of the casing is about 6 3/8 in diameter.

We had a thread about this subject, and to my surprise all the links and pictures posted are still working after 5 years.