It appears latent fingerprints are notoriously difficult to lift from some surfaces; firearms being one?
It depend son how the weapon is used. If there is a beating with it then you are more likely to find prints particularly when the weapon gets blood on it. The typical handgun you have less chance of leaving prints than a rifle which you hold in two different places. If you are beating someone with a handgun then you have more chances of touching other areas and leaving prints.
The weapon got blood on it from beating Nevill so the killer stood a good chance of leaving their prints in blood if not wearing gloves. Moreover there is no way the gun is the only thing that got hit with spatter so did the killer so the killer was hit with Nevill's spatter. Worse still the rifle butt broke where the killer's hand would be. At minimum the killer would have been scratched by this if not outright cut. Only gloves would prevent that from happening. Subsequent to it breaking the killer had to place their hand on the broken area to shoot the gun. Blood was found on that area and obviously it got there because the killer's hand had blood on it. No prints were left it is obvious the killer had a bloody glove that transferred it. This and the evidence Sheila didn't load a gun is supportive of Sheila not being responsible. The coup de grace though is the evidence she can't have killed herself. When you add this to that evidence it paints a complete picture of Sheila not doing anything and being framed as opposes to saying she had a helper who stabbed her in the back and then escaped.
The non-fatal shot is highly significant for a reason most people fail to appreciate. That non-fatal shot caused her neck to fill with blood and that is what ensured that drawback would occur. Because drawback would occur that means her blood would get in the muzzle of the weapon directly if no moderator was used or in the moderator if it was used. If she was killed with one shot then drawback would not have been sure to occur. So it was an important screwup.
Maybe the jury would have convicted anyway based on Julie's claims in combination with everything else but maybe no we have no way to know.