I need help identifying this 1.10 caliber projectile

If anyone could help me identify this projectile it would be vey much appreciated. The research I have done leads me to believe it was ammunition for the 1.1"/75 (28mm) Mark 1 and Mark 2 WWII era anti-aircraft gun (also known as the “Chicago Piano”). The caliber is correct but the length and weights do not match the descriptions for the weapon’s ammunition on this site: http://www.navweaps.com/Weapons/WNUS_1-1-75_mk1.php This site shows the length of the projectile at 5.8" and a weight of 0.917 lbs.

Measurements taken with a caliper:
1.109" at the base (below the rotating band)
3.455" total length
7.995 oz. total weight

Rotating band material is copper

Is it possible that this is a practice round for the Mark 1 or Mark 2 weapon?

Could the different corrosion at the tip be an indicator of the munition type? My uneducated guess is that it has something to do with a cap that was once on top the round, like an armor piercing cap (APC) like what is described on this site.
Any insight at all or any reference material that you can provide would be very helpful. I have more photos if that helps but I can only post 1 at a time on this board because I am a new user. Thanks everyone in advance!!


Welcome to the Forum!

The 1.1" 75 Cal. projectiles have some very distinct features that differ from your item including a very wide rotating band and an appendage at the base to house the tracer element as shown below.

These are the only three types of projectiles for this ammunition that I am aware of.

Hopefully someone else can help id your find.


This is very helpful, now I know to stop barking up that tree. Thank you for your insights, it is much appreciated!

I have found a similar looking round on a couple message boards (including this one). My round looks very much like the 30MM T328 discussed here: https://forum.cartridgecollectors.org/t/30mm-t328-ap/9771 and here: https://www.ar15.com/forums/general/What_30mm_projectile_do_I_have_here_/5-1878582/

From what I have gathered it seems the T328 was experimented with in the 1950s.
The examples I have seen online look very similar to mine (although none corroded like mine), except for the rotating band. The rotating band on mine has evenly spaced, rectangular shaped flares. The examples of the T328 I’ve seen have a smooth band with wording and numbers impressed.

Is anyone familiar with the 30mm T328? Thanks again for any input you may be able to provide!

it looks to me like the “evenly spaced, rectangular shaped flares” are rifling marks from being fired. The propose of a rotating band is the take the rifling, provide gas sealing, and impart spin with out generating excess wear to the rifling which would occur by imparting spin on the typical steel body of a projectile.

Forgive me if I’m telling you something you are already aware of.


Thank you for taking the time to help me out! I was aware of purpose of the rotating band, but I was not aware of the rifling marks left on the band after firing. I suppose this what is being referred to when law enforcement and CSI investigators match bullets fired from specific guns? Thanks again!

Yes the forensics folks use rifling marks, (and other markings) to match firearms to evidence found at crime scenes.

Although on small bore (typical hand guns & shoulder fired rifles) rounds the bullet jacket is not naked steel as is normal / typical in large bore projectiles but has a gilding metal or cupro-nickel coat over the steel jacket to serve as a lubricant & not wear out the barrel too fast. Thus no need for a rotating band.


The T328 projectile is very close in length, diameter and profile to the item you show. The advanced corrosion and the fact that it was fired likely into something may explain the lack of any defined flat nose.

Any idea where this was recovered?


Be aware that this projectile could contain explosive material.

Just because an item is old or corroded, it does not mean that it is inert. In fact some types of explosive become more unstable with age.

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Sorry, probably not the right place for this, but just joined after researching my find today. I came across 5 ammo containers for the 1.1 /75 cal. Thought I might find someone with some interest in them. Not sure how to post a pictures yet.