Older urethane balls had more urethane in them than do "modern" urethanes, which are really blends of urethane and resin, in order to get more length.

Older urethanes tend to hook fairly early requiring more ball speed to enable them to conserve some energy. Modern ones get more length, more like resins, to allow you to use them better. Bowlers who never used older urethanes also prefer the better length and feel comfortable, mentally and physically, using them. I think older players feels more comfortable using the earlier rolling, older urethanes.

Charlest is our resident technical expert on covers and all things bowling balls!

However, from a layman's point of view.......when you are able to "lock-in" on a release and breakpoint using the older urethanes.......regardless of how the pattern breaks down.....these balls remain remarkably consistent in motion, arc shape and carry! That's just my 2 cents.

I have a Blue, Black, and Burgundy urethane Hammer(s) from the 80's.

No most core numbers then are used now. The karma urethane is a very early urethane ball. It is also dull. Many of today's urethane are polished, pearls, or have a box finish near 4000 grit. Many older urethanes were much duller at box finish. Not all, but many. Adjust surface of today's urethane and see a difference.

So, the cover/core combo in several older urethane balls is better than the modern ones?

I think the specifications for manufacturing bowling balls in the late 1980s and the early 1990s allowed for lower RG than now. I read somewhere that these ball specifications were altered in 1994. No details about these altered specs, though.

Not better, in general, just different. I think that whether you think the older or the newer ones are better depends on your games, what oil conditions you face and your bowling reaction references.

Many of the newer ones are quite eary reacting, just like the old ones; The include the Columbia U2, Brunswick Karma urethane, AMF Hype Urethane (had one; VERY, VERY early rolling), RG Grenade, Storm Natural, a few others.
Please don't tell me yours, if included in the above list, doesn't roll early if you have 20 mph ball speed and 250 rpms.)

The urethane/resin blends of today tend to go longer than the dull, sanded solid urethanes of the 1980s. The resin part allows the ball to get more length, save more energy and have ore backend than many of the older urethanes.

Most/many of the older ones had simple pancakes core and even the Hammer cores, while being more dynamic than a pancake core, still flared very little compared to the newer ones.

The RG minimum was recently (last 5 years or so) changed from a low of 2.44 to a low of 2.46 or 2.47. I don't recall as the change was of so little importance that it was no change at all. In any case, as someone already said, most of the older ones never had RGs that low. Their hooking ability came almost strictly from the cover, not the core.

The old Hammers started turning as soon as they hit the lane. I got rid of all of mine in the mid 1990's when I accepted the fact that I couldn't hit the head pin with them. They hooked so early and so much that they hit really soft due to the expended energy. I have a hard time believing they would work on the standard house shot today. I know I couldn't throw one because I need my ball to skid.

I am very good friends who works with one of the big companies out there. I have had this talk with him. Charlest kind of had it right when saying the older ones had more urethane in them. Not even talking about cores the main difference is the chemicals used to make the urethane have changed. The chemicals used back then are either not available now or are at such a high price that they are not feasible to purchase and use for bowling balls. I am a chemist and doing my job over the past 15 years (having nothing to do with bowling) have seen chemical prices change and even not be available as easily as they once were. So changes have to be made to produce the next best option

Likely because there has been so little urethane available that many bought up or found what they wanted at bowling alley racks, pawn shops, garage sales, ect.

As far as cores, like mentioned most were pancake at first before going to light bulb shaped cores ect. The JPF Axe and Brunswick Phantoms had the most advanced of cores for that time.

The original blue hammer core

http://www.bowlingballvault.com/companies/12-hammer/1052-blue-hammer

http://www.bowlingballvault.com/companies/12-hammer/1054-burgandy-hammer

the new release blue hammer

http://www.bowlingballvault.com/companies/12-hammer/1529-blue-hammer-remake

Similar cores specs, one is 800 grit one is 4000 grit. Big difference on the lanes.

The more advanced urethane cores, the Phantom

http://www.bowlingballvault.com/companies/3-brunswick/580-phantom

But, you don't see many people using them. You want early, any of todays bowling balls at 800 grit will give you early. Many on most conditions will give you hook stop reaction urethane like from years ago.