I didn't feel like critiquing your squat because honestly it was very solid lift, but like anything there are things you can do to improve it.
I can't see your toe flare in the video so all I can say there is make sure your toes have a good 25-35 degrees of flare. This takes stress off the knees even if you currently don't notice any stress there.
Alright so this is how I would critique your squat.
1. IMO, I think you went about the whole process abit rushed, but I know you were amped for a pr.
2. Bring the bar lower on your traps. You are essentially squatting with an athletic squat width yet using a high bar placement. You would be stronger bringing the bar down another 2-3 inches on your traps. Ideally the bar would appear to almost be sitting on the rear delts or slight higher up.
3. Tighten up more in the upper back. It appears the weight is sitting comfortable on your upper traps, but I can tell you aren't fully tight in the upper back. Squeeze your elbows together as if you are pulling them towards each other and also try to raise them up in the back. Notice how your elbows are almost straight down the whole time. You can't get maximal upperback contraction like that.
4. Take 2 steps total when unracking the weight and setting your squat stance. You take 3 back and then 2 tiny little side steps to position your feet. This is burning energy even if you don't notice it. This weight for you while being a pr is not way up there in the stratosphere of what your max potential is. When you have to walk out 600 or more pounds the walkout can tax quite abit of your strength so being as proficient as you can in walking it out efficiently will only aid you in time.
Take 1 step back with the toes of the foot being in line or a couples inches behind of the heel of the other foot. Notice this is a small step back compared to how you see most people walk the weight out. Also work on setting your foot angle when you step back. No try to step back with the other foot and set it at the proper width and angle in 1 shot. Now make any last second adjustments to toe flare. If you walkout perfectly you can do it in 2 step with no extra positioning of the feet. TRUST ME this will make a HUGE difference when you really get into BIG weights Glad.
5. Your descent was very good. The speed at which you went down was controlled, but not too slow. The depth was a "tad" questionable. That would have passed most pl federations depth, but aim to break parallel with the top of your thigh. I would say you hit parallel, but if you can learn to squat an inch or 2 lower it will only benefit you and also place greater load on your hamstrings and glutes.
6. Your head position throughout the lift was good and I wouldn't change it. The only thing I would say is make sure you are looking slightly up throughout the whole lift. I can't tell, but it seems you are looking forward. Looking up reinforced upright posture.
7. This is the BIG one. Everything else I have mentioned is just little tweaks that will aid you when squatting heavy weights. When I said to tighten the upperback and pull the elbows together and up higher it really comes into play when you start rising out of the hole. If you are purposely trying to hold your elbows up as you descend into the hole as soon as you hit depth you can then cock them forward hard as you go up. This reinforces the chest up position and counteracts the effect of the weight wanting to bend you over. This combined with looking up the whole time both greatly help in maintaining good form while rising up.
8. Take a big breath into the lungs and the tighten your stomach. Then squat down. I saw you do 2 little short breaths, but you did not inhale into the chest. Creating a big chest and purposely tightening your abs again reinforces position when you start to rise. Because of your shirt I cannot tell if you were squeezing your abs.
9. Breath out through pursed lips/teeth as you rise up. This seems to help for some reason. Until recently I would hold my breath through the whole lift and now that I release a little air on the way up it seems to aid in stomach tension.
Well that's the jist of it. I wrote a very thorough writeup on the squat in my log which pretty much says the same things.
This is all minor stuff Glad. Your squat overall was good and far better than most videos I see posted. IF you take this to heart and work on these things it will only help to improve your squat form more which in turn will pay dividends as you squat bigger and bigger weights.
I myself have only recently learned alot of these subtleties with squat technique and they help tremendously.
One last thing to not is that the more you perfect your technique from setup, to walkout, to stance, bar placement, breathing, elbows etc the less you will think about the weight and the more you will be focused on performing a clean lift. This helps psychologically when handling bigger weights. My 405 squat was a pr and I wasn't thinking about the weight at allm but technique.
Hope this helps bro.
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