Is there a difference between 'old' urethane and 'new' urethane?
I think its more likely that the cores of the new balls simply create more flare than the old cores.
Wood is much softer than any synthetic lane. If you own an old Hammer and still have a place in town with wood lanes, the reaction is still as dramatic as it was in the 70's. If you take that same ball and throw it on a synthetic lane, it pretty much goes straight.
Modern cores weigh around 11 pounds. That's almost 75% of a 15 pound ball's weight. Back in the 70's, the cores were nowhere near that heavy and didn't have nearly the impact on the ball's reaction as they do now.
I have an old Faball Black Hammer drilled leverage weighted and it only creates an inch or so of flare on wood. On synthetic lanes, it doesn't flare at all. I might as well be throwing an 'ACE'.
It is more than the core.
It is really the coverstock that makes the big difference.
I have an AMF Angle Plus urethane that has a pancake weight block, but...Ron Machniak of Precision Bowling gave me a layout that is the equivalent of the PBA Plastic Ball layout, but for Full Roller.
This ball flares as much as my Widow Urethane, about 5 inches!
At Poway it is virtually unusable because it is so strong.
But on normal synthetic house shots it will not grab at all.
This cover was created for conditions of the 80's.
The oil is too slick today.
If the volume was real low it would work ok on synthetic lanes.
But House Shot volume is too high and too slick.
Same happens with The Judge, spare ball on normal synthetic house shots, but monster on low volume.
The one standout is The Grizz.
This ball at 320 grit will roll on modern house shots and with the simple CG in palm drilling I have on it, it does not flare more than one inch.
It is a pretty cool urethane ball.
I bowled a no-tap 300 with it at Poway and I actually had 7 real strikes in a row in that no tap.
I was using it at some new lanes and it was grabbing enough that I had to move in and play a 12 to 10 tip shot keeping it in the oil the whole way.
When the ball came back it had basically no oil on it.
I was puzzled and figured there was no oil on the lane and that is why I had to move in with the Grizz.
So I pulled out my rubber ball and made an up second arrow shot and the rubber ball hit the right side of the 3 pin.
It never moved an inch.
When I got my rubber ball back after that first throw it was drenched!
So what I learned is The Grizz was sucking up the oil like a thirsty Grizzly Bear!
It actually was absorbing the oil.
I really love The Grizz because it has such a tiny move left that I have total control with it and it keeps me way out of trouble.
Again this ball rolls hard but has virtually zero flare.
Here is a video showing it in action on the lanes I mentioned.
Watch how subtle this ball is in its overall movement.
It is the least moving ball I have, yet I favor this type of reaction.
This is why I love urethane.https://youtu.be/A3py5SauDXE