What Duane Hull said .....
"This "acclimation" sounds more like drive building than desensitization."
that makes sense, he thinks there is a reward coming and your not giving it to him. so he is making his own reward. I'd just correct with NO and then wait him out till he stops. You may need to say NO several times until he figures it out. BUt when he does reinforce with "gooood"
Sometimes the only "reward" is just a verbal "good".
That only works if they have a strong understanding of the markers. And it's probably not something an e collar will fix.
Take him all the way back to markers for a few weeks/months with toy rewards before introducing any gun.
tough situation to try and fix especially when you can't visualize.

i'd like to know what happens if you bring the gun out , go through all the motions as if you are going to fire it, but don't ?

I'm with those that see it as an obedience exercise. If your doing obedience when the gun is fired then the correction is for ignoring the command and not the gun.
Still start at a distance from whoever is shooting the gun.

i believe it's an obedience issue. 30 years ago chicago p.d. head trainer(at that time a 50 dog unit) explained how he trains dogs around gun fire. he would take the dog/s to the range start out a good distance away. as the officer's fire, then working his way closer all the time doing obedience giving the dog/s something else to think about. over the years i have seen handlers from other dept's bitten by the own dog during gunfire training i /we always used a muzzle if unsure of dog/s reaction. use Blanks just to be safe. me personally i would never allow a dog to grab a weapon good luck

bob i started typing about 10 pm lol any way what bob say's work's

 Quote: steve strom

I just think the first thing is to make him stop it. Set him up and let him know he can't touch the gun. Period. Since for the most part its when he see's it, I don't think you need to fire it in the beginning. Teach him to control himself, then think about the desensitizing.

Depending on your situation and child access, I'd have those firearms popping up everywhere around the dog - sitting on the coffee table, on the floor, on my side as we're out for a walk. Maybe even sitting in eyesight of his food bowl.

At the same time training a very consistent "leave it" command.

Pulling it out/picking it up and aiming (safely and possibly empty of course) on a daily, conditioning basis.

Go to the field with no intentions to shoot or fire at anything, simply bringing it out to train the dog.

 Quote: John Stopps

He's fine as long as I don't fire at anything, but as soon as I draw a handgun or put a rifle to my shoulder, he's trotting around the gun and making half-hearted attempts to grab it. If I fire, he'll go after it.

I don't want to get into anything big about the sensitivities of our dogs but there's a point of heightened awareness (excitement if you want to call it that), in us, where the target is in sight and our skills are on the line as to whether or not our aim is going to connect that bullet to it's intended target while maintaining the safety of everything else around it.

Matching that smooth draw, our positioning and aim without giving the dog any clues can be a rewarding effort in calm self-control.

And I'm not in any way insinuating any kind of emotional control issue but dogs can teach us a ton of stuff about our own actions. Figuring those out can be an eye opener for improvement in ourselves as well.

JMHO and two cents worth.