What is the lightest bullet that will stabilize properly through a 14"-16" 1/9 twist barrel (for .224" bullets)?
20-30 gr,30-40 gr, 45 gr?

Quoted: What is the lightest bullet that will stabilize properly through a 14"-16" 1/9 twist barrel (for .224" bullets)? 20-30 gr,30-40 gr, 45 gr?

What do you mean "properly stabilize"?  Longer bullets fail to be stabilized in slow twists.... not the other way around.  The other direction, too light of a bullet, is affect by what some call "overstabilization"  In my experience, that is pretty much a myth.  You didnt mention the caliber, so I am assuming you mean .223.

Velocity is a factor in this, as well, so it isn't just bullet weight/length.  My experience has been, 1/9 has no issue shooting ANY commercial .223 load (under 70 grains), the lightest of which I have seen is the 40gr VMAX and Noslers.

If the bullet doesnt fly apart, it will likely shoot well.  I have shot 45 grainers in my 1:8 twist and it groups them VERY well.  I have read that the super thin jacketed 40gr noslers will fly apart when they are fired in a 1:7, but havent seen it.

I think this is simply a function of how thin the jacket is, and how fast you push a light projectile.  In a 1:9, I imagine you could go even lihgter than 40gr if you wanted to.... but I havent heard of anyone using a lighter bullet than that in .223 rem.

I did mention the .224" sized bullets (same bullets you would use in .223 Remington). They will be used in 5.7x28 cartridges, but I have heard of keyholing when using 28 grain bullets through a 16" 1/9 twist barrel (hitting targets up to 100 yd sideways). These bullets are sort of different: they have a large hollow void in the tip and have an aluminum core.

Based on what I have read in the range reports, it seems like 28 grain bullets do not stabilize well through the 1/9 twist barrels (velocities aren't that high, about 2300 fps).

40 grain Hornady V-max were developed particularly for sporting use in the 5.7x28, but since we can also buy the 28 grain stuff, I just wanted to know if there was any particular reason why it would not stabilize or overstabilize? The weapon is a P90 / PS90, which uses a .224" bore (same style as the AR-15), 6 grooves, 1/9 right hand twist, in 16" length (not unlike the AR-15).