AT pro , how to be sure headphone and coil plugs are in all the way

Once you get to compressing the o-ring there is quite a bit of resistance. Just make sure you watch carefully that you don't shear off any part of the o-ring. Plus silicone grease works wonders for lubing the o-ring. The cheapest and thickest grease I've found is at Lowe's. It's in the plumbing section under plumber's grease. Just make sure it's the silicone type. Should be about $3.00 for a nice size container.

i get my silicon grease from a dive shop, it's the stuff they use on regulators.

anyway, after you tighten the locking rings, just try pushing the connector in some more and then check to see if the locking ring has gained any slack. if so, tighten it some more. i do find there's not a whole lot of room for big fingers when trying to turn those rings.
also, check those rings periodically when you're out in the field or before or after a hunt. if they weren't tight initially, they can work a bit loose.

Pete