You have experienced the chalanges in photographing long guns, which include the following:
1. To get the entire rifle, you need to distance the lens sufficently from the subject until you get the entire length of the rifle in the frame. Of course the amount of distance depends on the focal length of your lens, more for longer (Telephoto) lenses and smaller for shorter (wide angle) lenses. Remember that no mater what the focal length of the lens, the actual size of the whole rifle shown in the resulting picture will be about the same - small compared to the overall size of the photo.
2. Because the small size of the object in relation to a standard photo frame (4x6, 4x5 or 8x10), the only way to show the object in grater detail is to increase the size ot the photo - say increasing the frame to 13x20, or to crop the photo to show only part of the rifle while keeping the same photo size. Of course the former fix is not an option when posting the picture on this (or an) Forum.
3. Another problem in any acceptable viewing format is what to do with the extra vertical space in the photo you have when photographing the entire rifle. If you crop the photo to show just the rifle you end up with a very oblong photo.
How you meet these challenges is a personal choice. It helps to see how others resolve these issues by looking at coffee table books and magazines.
Below are some of the approaches I personally like.
I try to arrange the items in the picture to fill out the standard 4x6, 4x5 or 8x10 format as in the in picture of Win. Mod, 1890's below.
If I want to show a rifle in greater detail, I need to crop the rifle and retain the original size as demonstrated by the picture below.
If I want to picture the entire rifle in a single photo, I try to fill additional vertical space with additional objects as illustrated by the picture of the Bullard rifle below.
My preference for rifle pictures is to have a larger partial picture coupled with accessories as illustrated. below.
As I say, how you resolve these challenges is your personal choice. I have not found a single answer to be appropriate in all circumstances.