Gyrojet 13mm 2-Port


I have several 13mm 2-port gyrojets as shown in the photo below.

Previously, I have only see 4-port gyrojets. Is the 2-port version less common than the 4-port? Did the 2-port precede the 4-port version?

Can a gyrojet be sent through the US Post Office or does it need to go Parcel Post?

Any help and information would be greatly appreciated.



A Gyroject is small arms ammunition, and can’t be mailed. Parcel Post is mail. It can’t be sent that way. UPS or FED X is about it.

It’s a long story. Right now, I’m on page 314 of my gyrojet book.

The two-port rockets came after the four-port versions, and are seen in 13mm (12.94mm average outside diameter) and 12mm (12.54mm average outside diameter) rockets. Your magnet will confirm that these are copper-plated steel.

Briefly, two young engineers came to Robert Mainhardt at MBA to announce that they had invented a machine that would drill four ports simultaneously. Didn’t work, but the machine drilled two, which was good enough. Mainhardt bought the machine for the 13mm Gyro-Flares and discovered that the two ports worked well with the rocket ammunition.

Gyrojet rockets are small arms ammunition. UPS or FedEx.


John and Mel,

Thank you very much for the information.