canuckistan,
That would be a DGX-Bonded bullet, we hope, first of all,
as the old non-bonded DGX is an inferior bullet compared to the bonded one.
But at low velocities, even the old DGX might hold together and perform like an FN solid.
That is an incomplete way to say it, that it expands at up to 150 yards, according to Hornady, with no MV specified for that claim.
Also, we are left guessing if you mean the 500-gr DGX or the 480-gr DGX of .458 caliber or what ?
As Sir Meplat, I know you are wise enough to be using a .458 WinMag.
The Hornady manual shows this for the 500-gr DGX handloads from 24" barrels:
2200 fps for the .458 WinMag max
2250 fps for the .458 Lott max
That is about the most honest assessment you will find,
as the .458 WinMag is kept down to 60,000 psi and 3.340" COL
while the .458 Lott is allowed 62,500 psi and 3.600" COL to stay within SAAMI standards.
Current Hornady factory ammo with 500-gr DGX is an honest 2140 fps from a 24" barreled .458 WinMag.
For that load, at 150 yards the remaining velocity is down to 1760 fps, assuming BC = 0.295.
Is that the velocity that Hornady says works for the 500-gr DGX ?
If your MV is 2000 fps, with the 500-gr DGX,
150-yards =1636 fps
250-yards = 1426 fps
A .458/500-gr DGX-Bonded impacting at 1426 fps will probably make a bloody big hole through a moose on a broadside shot.
If you are zeroed at 150 yards for 2000 fps MV,
at 250 yards the trajectory is -14.66",
at 200 yards the trajectory is -5.47",
at 100 yards the trajectory is + 2.22".
I am thinking the 404-gr Shock Hammer would be a better moose bullet,
but the .458/500-gr DGX at 2000 fps MV will kill a moose at 250 yards with a hit in the vitals.
However, you might be in for some tracking.
Your choice whether to do your hunting only before the shot,
or maybe to continue hunting the same animal after the shot.
