It is a federal slug load....and it is prob 5-10 years old ( I hunt with this load- have killed a bunch of deer with this load since the 70's).....I have a bunch of WW & Remington slugs as well....that are current mfgr.....I haven't dissected any of those, but will when I have the time..Deer shotgun season is coming here soon and when I am at the store I will pick up a couple boxes of "current" slugs and we will see......I also have 16 ga and 20 ga slugs as well and when I have the opp I am going to dissect a couple of them and compare them to my full choke 20's and 16's as well.....frankly, I was surprised myself when the slug rattled down the barrel and plopped out of the full choke....goes to show you....regardless of how long you have been involved in this....always something to learn....I will let you know the results of my further investigations.
I will also break out the calipers and obtain some dimensions.