Interesting 300 H&H cartridge

[RCS]

I have had this cartridge for a long time and decided to try and identify this loading. The cartridge has the normal 300 H&H profile and headstamp - but the case appears to be aluminum with some type of partial black coating. The bullet looks to be plastic and there also appears to be a half charge of powder in the case

Any help would be appreciated

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Information

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[Lee Enfield]

the stained bullet and base resembles a proof load.

I'm not sure what is going on with the case? perhaps the stain has reacted with the case material in some way??

sometimes high pressure proof load cases were tinned.

[Sunray]

Gotta better picture of the head stamp? It say Super-X? That's a Western Cartridge Co., East Alton, IL head stamp. Winchester uses it too. They introduced two loadings, 180 grains at 3,060 fps and 220 grains at 2,730 fps. That case is one of 'em. No idea which.
There's a picture of that exact cartridge here. No other info provided.
300 HOLLAND HOLLAND MAGNUM | Cartridgecollector.net

[RCS]

Sunray, thanks for finding a picture of my cartridge, the head stamp reads SUPER-X 300 H&H MAG. Keep in mind the case is aluminum and
the bullet is plastic not a normal copper jacket.

Any indication what this cartridge is used for ?

[Merle]

Sunray, thanks for finding a picture of my cartridge, the head stamp reads SUPER-X 300 H&H MAG. Keep in mind the case is aluminum and
the bullet is plastic not a normal copper jacket.

Any indication what this cartridge is used for ?

my guess would be a short range gallery cartridge....

[Lee Enfield]

Sunray, thanks for finding a picture of my cartridge, the head stamp reads SUPER-X 300 H&H MAG. Keep in mind the case is aluminum and
the bullet is plastic not a normal copper jacket.

Any indication what this cartridge is used for ?

A red base and bullet is the common indicator of a high pressure factory proof load.

http://www.ammo-one.com/Proof-300H-H.html