I am not sure what the rg rating is on the Black Hammer which was the first Urethane that they made and was for medium to long oil and flared about 1 to 1-.5 inchs but you guys have forgotten about the solid red hammer which was the second Urethane hammer and it did flare 2 to 4 inches and it was my best ball for a very long time. I loved that darn ball but it was not produce very long because they had trouble with getting the red to grip the inter core,So they change it to the light blue ball ,but for some reason it just did not hit like the red ball.I drill most of the Hammer balls on the reactive side in the early days and the only one i like was the navy blue hammer.One last thing about the red hammer it was a dull ball but you could make it shine like a red apple and use it on short oil but you would have to take it to 2000 grit to make it shine like that.If you had crappy back ends like we did back in the day you could scoot brite it and man you could score like know one,Then the abc said you could not do that any longer but if you did it in the beginning of the night before league play it was good for the night.   

2.6 range and .020 range

If this is any help,This is from the original hammer website
(which you can find using the Internet archive wayback machine)

https://web.archive.org/web/19990506080648/http://www.faball.com:80/nails.htm



Technical Specifications - Blue Hammer
Hook Potential 1 – 20------10
Back End 1 – 15------7
Radius of Gyration------low
Coefficient of Friction------medium
Hardness ( D-Scale Durometer )------75-78
Flare Potential------2"-5"
Lane Conditions (Oil)------Medium to Heavy
Pin Distance from C.G.------0"-4"
Top Weight Range------2 to 4 ounces
Surface Finish------Factory Textured (600 Grit)
Available Weights / Core Type    
13 - 16 lb. Hammer Core
10 – 12 lb. Elliptical

Technical Specifications - Burgundy Hammer (yellow lettering) (Org. is white which is what I have)
Hook Potential 1 – 20------11
Back End 1 – 15------8
Radius of Gyration------Low
Coefficient of Friction------Medium
Hardness ( D-Scale Durometer )------75-78
Flare Potential------2"-5"
Lane Conditions (Oil)------Medium to Heavy
Pin Distance from C.G.------0"-4"
Top Weight Range------2-4 ounces
Surface Finish------Factory Textured (600 Grit)

Available Weights / Core Type    
13 - 16 lb. Hammer Core
10 – 12 lb. Elliptical


As for what does RG-low mean. Heres a couple of the old scales.

Simple RG scale (there are others):
Low RG: 2.460" - 2.570"
Med. RG: 2.570" - 2.680"
High RG: 2.680" - 2.800"

Here's another:
Low RG = 2.430 to 2.540
Med RG = 2.541 to 2.690
High RG = 2.691 to 2.80

Now Hammerheads, it's time for a little secret. Y'all can pick your all time favorite hammer from the above list, but as good as they all were, there was another that was better. Yes - better than the Blue, better than the Black. The Red Razor!  Since I finally managed to find my 15# Red Razor, I can spill the beans. The Red Razor got no respect - it was overshadowed by the release of zillions of reactive balls. But it is an awesome ball. It overcomes the one problem I had with the blue hammer - early hook. The high RG core in the Razor gets it through the heads pretty good, and the aggressive urethane cover gives it a monster back end - with no reactive flippiness. Here's a 1996 BTM review:

“There are balls and there are Balls, but the Red Razor was one of the true surprises of 1995. This is truly another of the unconventional urethanes. Although covered in a tweaked urethane name HPF (High Performance), this is one conventional that thinks it’s reactive. The Red Razor is a high RG ball that goes very long, but unlike the earlier generation of urethanes, this ball makes a definite snap to the pocket. It doesn’t hook in the class with the newer Brunswick, Track, Columbia, and Ebonite reactives, but nothing out there – reactive or not – throws more pins around than this Red Razor. And, one of the features that reactive snobs will like is that the Red Razor tracks like a reactive. No gentle arc to the hole. This one goes down and turns hard and nothing – oil or pins – stand in its way. If you are a bowler who is stuck on a condition where reactives keep you in serious trouble, but you don’t want to sacrifice power to gain control, give a good look at the Red Razor. This is Faball at its best. Control and power is tough to beat and this ball will give you both and on some of the trickiest conditions around. Appropriate for all but the oiliest conditions. Suitable for virtually anyone looking for a strong urethane ball.”

Granted this a massively zombie thread but was thinking of getting a red razor (to go with Burgundy I just got 2nd hand) but they are almost all 16lbs.  Also I came across this - http://www.ballreviews.com/faball/lichsteins-1997-ball-guide-faball-only-t257158.0.html - by same poster of comment.  Looks to me like the Red Razor is not stronger than the (old) Burgundy just more of the pearl like version (in behavior not actual cover stock) with more motion on the backend with equal or a bit less total hook (also 3 piece vs 2 piece of Burgundy).  I am thinking it probably behaves similar to my new version Blue Hammer with perhaps a bit more carry.  If that's the case probably only need one Faball in my arsenal.  They look nice though but getting close to spare ball strength (but not carry) on modern oil I fear (all synthetic lanes where I live).  Will see when I plug and redrill my Burgundy.

Cool old school Faball advertisement found on ebay.

Finally rolled the old Burgundy and I can see why it has such a legendary status.  Took a 240 grit brown scotch brite by hand to it and with surface on a house shot it was only about 5 boards weaker than The Crow.  The carry was close but The Crow was still a little bit better.  Still not bad for a 20 year old ball.  Will probably take a bit of surface off it and use for a full step under The Crow.  Can't wait to try the Red Razor on the way.  Thinking more and more I am going to try at least with league on house shot going with an all urethane and psuedo urethane arsenal (old Burgundy, Red Razor, new Burgundy, new Blue Hammer, The Crow and plastic spare ball, could probably use one of the urethanes but gotten real comfortable with now).  I love urethane, even the smell is cool as hell.

I love urethane as well!
I have:

From Visionary:
The Crow
The Judge
The Midnight Scorcher

From Hammer:
Black Widow
Purple Hammer (new)
Burgundy Hammer (new, not urethane, but really rolls like urethane)

From Brunswick:
The Grizz
True Motion

From AMF:
AMF Angle Plus

I love them all!
They really make bowling fun.
I generally hate resin and the resin reaction.

I dont think there was anything in the low 2.5 range prior to the ceramic cores which came out mych later.   My guess is closer to 2.6 rg on the original urethane hammers