How heavy of a bullet would a 1x12 24" standard (factory) .223 barrel handle?

Caliber?

Also, it's not the weight, it's the length of the bullet that matters.

yea, should have put that there .223 Rem.

Without consulting any charts or anything, I'd say you can probably use up to 60- or 62-grain bullets of conventional construction.

I thought that would be the limit for stable bullets.

I agree.

When I used a 1:14 .22-250, 55 gr is as high as I dare tried. Tom, you might try
up to 69 gr, but I'm not real confident in them.

I've always had success with that Sierra 63 gr SMP bullet in my 220 Swift. It's a short little bullet that I'll bet will stabilize in a 1-12 223 barrel. While that one would stabilize, don't even bother with the 60 gr Partition, the 64 gr Nosler BSB or the 65 gr Sierra GK. Of the last 3 bullets mentioned, the 60 gr Partition would stabilize (barely) in certain favorable weather conditions, so if the 63 gr Sierra does stabilize, you might try a few Partitions.

Thanks guys, I don't have any 62/63gr bullets but I do have alot of 55gr Nosler BT and HP's so I'll stick with them. I can put 3 in a 3/4 sticky at 100yds and I think I have reached this barrels best. and 2 where touching.

Basscat, the 60 gr hornady sp might be worth a try. I load for a 24" rem 700 with a 12 twist. It's sweet spot seems to be 50-55 gr, but It will shoot the 60 grain hornady sp well. It is a flat base bullet and it needs to be moving pretty good before it tightens up out of my 700. If you decide to give it a go, I would pick your powder with that in mind.