I bought a few hundred bmg.  looks like most of the ammo hav no paint markings left.

does the fmj have a lead butt plug (about 3/36" of a inch diameter after the mild steel
AP has the copper fmj hole with no lead

tracer should have the foil backer correct?  doe it have the same mild steel as the fmj?

thanks

Lots to cover here......

First, remember that the headstamp only tells you when the BRASS was made and where.  If it's an original round, yeah, that's the place and date of mfgr of the cartridge, but there's a ton of ammo out there that's reloaded, so what load it is, who made it, when, etc. is up for grabs.

The lead in the base plug for Ball, refers to Ball M33, 1951 or to current production.  The predecessor Ball M2 just had an exposed steel core base, with the bullet jacket rolled and wrapped up around it.

API M8 also has a lead base plug (white or silver tip, depending on year of production).  AP M2 (Black tip) is like Ball M2 in that it has the exposed steel core base with rolled over jacket.

Early tracers did not have any kind of base cover, till the 1950's, then the foil or plastic cap comes into favor.  Prior to the 50's, it was just exposed tracer powder.  They found during WW2 that tracers only traced till about 18 months after production, then they wouldn't burn any more.  Research found that the compound absorbed moisture from the air in the case and the powder, inerting it.  Adding a cap expanded the shelf life considerably.

PLAIN tracer (red tip, orange tip, brown tip) doesn't have a steel core.  Just a lead nose plug and the rest of the bullet filled with tracer compound.  Starting mid WW2, they started producing tracers with Gilding Metal Clad Steel bullet jackets (GMCS).  Prior to that they were Gilding Metal (GM) jackets.  The switch was to reduce the huge amount of copper being sucked up by wartime ammunition production.  GMCS jackets were steel jackets with just enough copper to protect the steel from rust.  They look identical, a magnet will tell you which is which.  Starting in 1984, the PLAIN tracer M17 was changed from a bullet jacket filled with tracer compound and lead, to basically a ball bullet with the mild steel core drilled and filled with tracer compound.

PLAIN tracer is M1 (Red tip), M10 (Orange tip) and M17 Maroon (or brown) tip.    M1 was built from the 1930's to the end of WW2.  M10 was only built a couple years in WW2.  M17 started late in WW2 and continued till 1984, when it was changed.  (There were some other tracer designs, but didn't last long)

APIT started in late WW2 (Red/Silver tip) till today.  It was essentially an API bullet drilled & filled with tracer compound.  in 1984, the APIT was changed to Red/White tip.

Collectible?  Depends really on whether it's original or not and which bullet load.  Ball, AP, API, Tracer are only a couple bucks a round, about shooting grade prices.  APIT maybe a little more.  But the earliest API and APIT I've ever seen were 1944, not 43.  Original primers, of course, were corrosive, so that impacts pricing as well.

Hope that covers it.  If you have more questions, feel free to post again.