Well, what's the heaviest subs we can cycle in an AR?

What options are there for casting boolits?

I am just curious.  Seeing as we are limited by speed, the only way to add energy is with more mass, so if I was chasing K.E., how heavy could I get it?

btw- I don't have any depleted uranium, so that's out of the question.

Don't know about an AR, but these are pretty heavy.
http://www.missouribullet.com/details.php?prodId=182&category=6&secondary=&keywords=

I've used 250 gr Sierra Matchkings in the past.

I can't disassemble my can so I stick with jacketed bullets.  The heaviest one Sierra lists now is their 240 grain HPBT, but holy smoke they're proud of them.  For more economical shooting, I like the Hornady 225 grn HPBTs.  They cycle swimmingly well in my 9" Noveske tube over a midweight charge of 1680.  You can find that bullet on sale for as little as 31 cents a pop.  That's nowhere near cast prices, but at least it's not Sierra prices, either.

The bullet casters like me have mostly settled on 240-250grn bullets. Most are powder coating. There are a few molds specific to the blackout out there. I can also run them at lower velocity  and use less powder because of the weight. My cast subs run in the 980fps range. Less powder equates to better suppression in my experience and heavy bullets make a really nice "thud".