Hi Briony,
I'm glad that you haven't given up with this

There really is a lot to learn through doing a 52 and you're guaranteed plenty of feedback and support.
And I happen to think that there's a lot to like with your rifle image

It's a good interpretation of the theme, lovely & sharp and there's some very interesting detail in there.
In terms of how it could be improved, John has already summed up what I wanted to say (as usual

)
To make it more interesting.. if you can... stand it up, put the camera low down, as if you were sighting along it, got for a relative small number on the Aperture, and get in quite close and see what comes out... Maybe play with the aperture a bit.. focus on different parts of the firing mechanism and barrel etc.
With this type of shot, experiment with some different viewpoints and angles. Get in closer to some of the detail, tweak the aperture settings to see what effects you get. It's a great way to get used to the different capabilities of your camera.
And then we have "Play" : (Your BIF)
OK . . . all this time you've been telling us you can't do it and you want to give up . . . and then you go and post something as brilliant as this
I know absolutely nothing about bird photography, but I'd be very happy to get something like this.
Wildlife and animal photography is obviously your passion, so why not see if you can try to incorporate it into the rest of your 52?
The themes are just there to prompt you to get out with the camera and give you a bit of inspiration. It really doesn't matter if there's only a tenuous link to the theme (although you might come in for some playful teasing for it)
Have a look at Leanne's (Shorty's) 52 thread from last year.
She really wanted to work on her pet photography, so you can see how she fitted this into some of the themes. You'll also see how her pet portraits improved over the course of the year.
Part 1 and
Part 2 here.