[Unclenick]

All powders are dirtier at lower pressures. This is because temperature increases with pressure in a powder burn, and higher temperatures result in more complete combustion; particularly of the powder at the base of the bullet that moves down the bore with it. That powder is running at a disadvantage because of the pressure gradient that drops pressure right behind the bullet as compared to the pressure at the chamber end.

Yikes! Now you've gotta worry about the frigging pressure gradients on top of everything else! Well, not really. Yes, technically this is rocket science, but no, you don't need to know all the details. All you've got to keep in mind is that the lighter the bullet, the faster a given pressure will accelerate it. The faster it scoots forward, the faster the powder has to burn to make gas fast enough to keep up with it. That's where Varget gets into trouble with 50 and 55 grain bullets. Yes, compressed loads can be made that will shoot well with Varget and those light bullets in some chambers, but you risk secondary pressure spikes in barrels 20" and over, and you burn more powder weight than you would if you were using something more efficient for that bullet weight, so it's costly. I've had good results with Varget firing 69 grain match bullets and heavier, but with 50 grain bullets I use either IMR4198 or H4198, and with 55 grain bullets Reloader 10X is about as slow as I like to go.

Long ago, Julian Hatcher suggested that you want to look for powders that produce ballistic efficiencies (the percent of chemical energy stored in a powder that is translated to kinetic energy in the bullet) of about 30% in medium power cartridges (like the .30-06, .308, and .223). With a 52 grain A-max or a 53 grain Sierra MatchKing in the .223, maximum loads of IMR 4198 will produce ballistic efficiencies of around 31%. Reloader 10X will get to 29% (these are according to QuickLOAD). Varget has trouble making 23% even if heavily compressed. Indeed, the peak pressure is below the usual starting load range when you use these bullet weights and Varget, even when the Varget compressed a modest amount.

The result of that low pressure is incomplete burning and higher charge weight than you would need to get to the same velocity with the other powders I mentioned. Among them, IMR 4198 has an excellent accuracy reputation, and you won't likely exceed 22 grains of charge at peak accuracy and pressure. 10X has developed an increasing following and will get you more velocity than 4198, and the charge will still be around 23 or 24 grains. At that, it gives about the same velocity as 27 to 28 grain compressed charges of Varget. So, 10X is more economical to use, runs at pressures nearer the normal peak cartridge pressure, and therefore burns cleaner.

I recommend you get one of the 4198's or the 10X for your light bullets and save the Varget for heavier ones or for .308 or .30-06 loads, where it really shines, IME.