It's a subscription magazine with the history and some technical descriptions + a manual for building the model + the parts necessary to build the described steps in the magazine.
`And it's a bloody expensive way to build a model.
To be brutally honest, the "subscribe to our magazine and build a model" always feels a bit like a scam to pull more money out of unsuspecting buyers. The resulting models are usually none-too-bad, but not outstanding, or worth the price of the subscription.

If You really want a gun like that, I wouldn't be surprised there's a reasonably accurate garage kit of it somewhere for a fraction of the price.