I am fixing my Bravo upper and it has a Timken 387 AB bearing and 383A race, I have a timken 387A bearing in the shelf and it appears to be the same , I can buy a 387A all day but not finding a AB even on Timkens website, anyone know the difference if there is one?

No difference . load it up

The B must stand for Bravo!!

or BROKE

Blowup

I went to a bearing store and bought a Timken 387 AB this week, they had them in stock

I saw a master bearing Catalog at auto parts store yesterday, the 387a had more radius on the back side where it would seat, the 387as had even more radius but no 387 ab listed , there is virtually no fillet radius on the xr pinion gear anyways so its irrevlevant. Fwiw too my old bearings I dug out from last time I been thru drive had just a 387 with no letters, Smitty

Try calling one of your local bearing suppliers.

Its all in the radius, and the radius isnt needed anyways so any of them will work, thats what I found, Smitty

No radius? maybe thats why they are quick disconnect shafts.