By then he should be over the pop shyness. Make him relate the pop to something he likes and wants.
By then he should be over 150 pounds...not trying to discredit 2MANY's method here (it obviously works for him) but I think you'd be hard pressed to find any professional trainer that uses the Oscar Meyer method to cure any possible gunshyness.
Yes, it is important to make him relate the "pop" with something he likes and wants, but that "something" should be birds and/or retrieving, not food. When the pup is young it is recommended to make noise while
they are eating, like banging pots and pans and slamming cupboards and such. Personally I wouldn't introduce the food bowl to any portion of field training. The food bowl is for dinner, period.
I ran across this dog joke a while back that pretty much illustrates just how easy it is to train a lab versus other breeds. They are perhaps the most eager to please.... How Many Dogs Does it Take to Change a Light Bulb?
Australian Shepherd: Just one. While the rest herd the property for any more light bulbs or even light switches that need to be replaced.
Pit Bull: As long as I'm here, nobody can change ANYTHING. Not as long as I'm breathing. NO WAY.
Golden Retriever: It doesn't matter. Even if someone breaks in, I will find the flashlight for them and show off all of my toys and will play fetch nonstop. I still got lots of toys that squeak.
Labrador: Oh me, me! Huh? Huh? Pleeeeeeeeease let me change it! Can I? Can I? You sure you only want me to change it? Too bad these bulbs float, or else I would even change the ones from way under the pool.
German Shepherd: Roger that. First of all, I need to see if that is truly a light bulb or a bomb. Second, I'll check for any intruders still left in the premises.
Maltese: Let the German Shepherd do it. Cocky bastard. You can fix my hair.
Border Collie: Just one. And then I'll replace any wiring, check for any hazards, and let you know how long that light bulb will actually last.
Siberian Husky: You mean just yank it out of that ceiling and take off with it for miles without even looking back?
Jack Russell Terrier: Dude, I have cats to chase, rabbits to hunt, and make my owners catch me if you can game. Besides, I will pop it again with my constant bouncing around anyway.
Bassett Hound: Leave that thing off. I am so tired and sleepy and I love it when it's pitch dark. Too much light hurts my eyes.
Poodle: Oh come on. Give me a break. Who wants to mess up the hair for a stupid light bulb? What if the minute I even try to install it, it fries my awesome fro.
Doberman: Let them break in. I always wait in that corner and never make a sound. By the time they notice me, my teeth will meet their crotch. Then we’ll talk about who’s really going to get neutered tonight. GRRRRRRRRR.
Beagle: Light bulb? I don't sniff any light bulbs? What's the point. I will pop it again with my long piercing barks anyway.
Chihuahua: Yo quiero TACO BULB?
Bulldog: No way Jose! Last time I tried that crap, I landed flat on my nose.
Pointer: I see it. There it is. That one right? Yep I see it. There it is. Right there.. hmm.. although it is not moving.