M220 Target Practice Tracer projectile for 20x102mm Vulcan M50

This is probably a 20x110mm US Navy projectile. It says “M221 GLN80K001-002” and what looks like multiple “T” along the periphery. Nothing on the rotating band. Someone sheared a small portion and put 4 little drill holes. Why?

The red T’s indicate tracer!


Its not 20 x 110USN.

This proj, (TP-T) conforms to the M55 style, M221 USN designation (20x103)

Info below from Aviation Ordnanceman (USN)



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Many thanks to both of you. I’ll weigh it tomorrow at work.

What looks like “little drill holes” are in my opinion Brinell hardness measurements (spherical). To obtain correct readings, the paint was removed.


Cool, so somebody did not trust someone’s supplier, otherwise they’d test it before applying paint (if that were their own metal) https://www.youtube.com/watch?v=RJXJpeH78iU.

Might just be an inspection or investigation if their had been an incident involving that batch. Wouldn’t normally do that to a loaded (albeit tracer) projectile.


This projectile weighs 97.84 grammes which is 1509.9019 grains. It also lost some weight because of that Brinell site. The table above indicates that the weight is 1470 grains. Is that a normal (standard) deviation from an average weight?

100% agree - hardness testing. USG contract might have required testing at the LAP facility. They are trying to buy off certifications more these days, however 10 plus years ago they often wanted you to double check.

Also, if you got some weird issue in production or test firing someone would have said to double check the hardness. They typically buy a tracer pellet and then press it into the projectile. The tonnage is enormous and if something caused a problem (bad tracer because the pellet cracked) they might suspect the projo of expansion and contractions.


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