Good answer! Damn. There's really not much left to say now, so about my hunting trip...just kidding!
The one thing Harry mentioned that I especially wanted to comment on, is a wrestling match. I have been fortunate enough to never have been in any real combat, but in training, I have found that, if you have to wrestle around, you (gg) are probably screwed, or at least a much higher percentile than one would like. Make it work fast
As I have mentioned previously, one method that the perp does not usually anticipate at close quarters, is being punched or "speared" with the gun barrel. One very effective grappling/strike move the Bujinkan teaches is in response to a arm grab and pull attack, presumably to be followed by a strike. The perp/uke/attacker expects resistance, and generally puts a good bit of force into the pull. If the defender can just touch
the opponent's grabbing hand with the back of their free hand, they will subtly lock it in place long enough to not only not resist the pull, but to step with it, driving the elbow of their "captured" arm into the sternum of the attacker. Ow. In the same manner, if the opponent viciously pulls your longarm towards him, go with it. Add some momentum. There are obvious targets in the upper body. If the opponent's arm is down during the pull, and the primary weapon is pulled at a downward angle, this spearing attack I am mentioning can be directed toward the pelvic area, above the pubic bone. A good strike anywhere in this area will tend to fold the attacker. If one manages to strike where the hips join the pelvis, it both produces an excruciating strike, and spins the attacker's upper body away.
Depending on the legal mores of your situation, and the stupidity of your attacker, one has another choice. Again, the circumstances will dictate if this is an option, but one has the option of letting your opponent shoot himself with your weapon, if the attacker has the muzzle in line with his body. Heck of a retention technique. (I used this one when I was 7 against a much older, and stupider, opponent. The BB hit him just
above the eye.)