I can do 405 for a couple of reps (2-3), my grip is very weak and I won't wear a strap..
to be honest I don't think that I have the form right..I think that I am bending my knees too much. I look at that Coleman clip and his form is interesting, barely a knee bend..also I make it a point to never curve my back
the fucking trainers at my gym are totally useless asking them would be pointless...and no one at my gym does them with any serious weight so there is no one ask questions of.
The back is the biggest muscle group in the (upper) body and you need to use straps to properly exhaust it mate - you need to move a lot of poundage to stimulate growth and thickness and you shouldn't be worrying about your grip or your forearms.
You should just train forearms separately. When it comes to back day, you need to use straps and if needed, a belt. And forget things like pulldowns and seated cable rows - they are good for getting some blood in there, but to get a lot of mass and thickness, you need to deadlift, bent-over row and Tbar row heavy weights.
As for doing deadlifts - to be honest I think that a lot of the trainers have it wrong. They can tell you what the correct form is if you are doing 1 plate a side, but when you're lifting upwards of 400 or 500 lbs, you are going to be rounding your back a little. By the time you get to that level, you'll know if you're doing something wrong (although not always, of course).
If you have thick spinal erectors, you can round your back a bit and it's not going to kill you. Of course, I'm not saying just use whatever form without worrying, but just that don't be afraid to let your body assume whatever stance it does when it's moving a lot of weight - it's an inbuilt mechanism that you'll know only if you've lifted heavy and not some fancy thing you read about in Mens Fitness