[Vplayer]

It could be a combination of things, mainly mechanics. We all have the same skeletal structure, but we all have different mechanics in the way we move, reach, and other things. A good example is walking: we all walk with the same two legs moving the exact same muscles. Yet everyone's walk looks different. Same with the rest of the body structure. Your issue could be flexibility, or even the type of muscle fibers. Or both. One of my friend's biceps muscles are such that he gets an extreme pump just holding the bar for squats. As a result, he hardly ever trains biceps, yet they are absolutely huge. He just won the overall novice at the Ronnie Coleman Classic if you want to look him up.

There's several things you can do, starting with something called resistance stretching. It's not static stretching, it's much much safer. Get a a little more flexibilty in there and if that doesnt do the trick, there's things you can buy like Dave Draper's Top Squat that will take your arms out of the equation. Just a couple ideas, bro.