Line Drawings of 20mm to 30mm Cannon Rounds & Others, Experimental (1970's Texas Bull Shooter Bulletin)

I decided to post these drawings from the old Texas Bull Shooter since they provide good basic information on a number of US experimental cannon rounds dating from the 1950s to the 1970s. Most if not all of the drawings were probably done by Robert Mellichamp and much of the information was provided by Bob Leiendecker (Past head of the Large Bore And Artillery section of the ICCA Bulletin) and Ralph Meyer.

Image quality- Keep in mind these are photos taken straight from the bulletin pages which in turn were produced via 1970’s vintage photocopiers.

30/20mm USN Exp., 30mm Grenade Cartridge, 20mm Caseless


30 x 120mmRB & 30 x 137mmRB SURE Gun U.S. Experimental


27mm-30mm Exp. Cartridges


26 x 130mm Colt


30 mm Cartridges Manufactured By AMRON


Some information on 30mm Aircraft Cannon Rounds, 1974


30 x 173mm GAU-8




Thanks ,thats great.
I actually have one of the 30/20 USN rounds, if not the one the drawing was made from. Everything is the same, though i always thought it was a dummy of some kind as the 30/20 adaptor only provides a seated friction fit, no option for crimping.
I guess Tony W will be keen on the 30mm WECOM drawings .20USN 30


Brian, thanks for these drawings!

Takapu, the adaptor was probably to be soldered and your case might be unfinished.
Also the adaptor appears to be solid brass (if this is the original design). Means there is a good chance that it will not separate from the case anyways as it will stay in the chamber when fired and later will be extracted together with the case.
Just my thoughts.
Of course it would be better to have the documentation on this one rather than guessing.

Missed one intended for the post above (20mm Davy Crockett Spotter) so posting it here-



Yes, the adaptor is turned brass, sweated to the case. My comment was more the projectile is just a friction fit, though i guess it could have been glued?.

Thanks Brian!

The one which interests me most is the 30 x 111 bottlenecked one in the third page down, identified as being a Bushmaster - that was, in fact, the first iteration of the WECOM. Still no info about it…

…or about the one shown below, which has a steel 25 x 137 case necked down to 20 mm. Anyone know anything about it?


Tony, is this 20mm still 137mm long?


There is no headstamp or any other form of markings anywhere.

I have one of these. It was labeled “Raptor F22 XPTL”.

Knowing next to nothing on the subject, the necked-down case in your picture has a very chunky rim, is there a reason for it to be thus ?


Do you mean the 20 mm or 25 mm version?

I have no idea, Peter. The usual reason for a thick rim is to survive violent extraction forces, but I don’t know why that would be, if it was being used in a rotary gun.


The 25 mm steelcase necked down to 20 mm

Thanks - did the “Raptor F22 XPTL” look official, or was it just hand-written?

Hand written informal. Probably embellishment by the seller :)

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