One of the "problems" here is that what people are calling "carbon" fouling is not necessarily all carbon. Yes, smokeless powder is partly carbon (one of the basic chemicals in nitrocellulose), but one of the reasons very slow-burning powders--such as RL-26--burn so slowly is powder-granule coatings that by definition resist burning. Thus they leave some residue in the bore.
Which is one major advantage of the Belgian-made Ramshot rifle powders. Their deterrent coatings are apparently designed to burn once pressure (and the accompanying heat) reach a certain level. Which is exactly why they leave considerable fouling until pressures reach around 60,000 PSI--whereupon the "carbon" fouling almost disappears.
Personally, I haven't been that impressed with RL-26. While it does result in an increase in velocity in many cartridges, I have found it more temperature-sensitive than Alliant implies during my testing from zero to 70 degrees--which has resulted in significant point-of-impact shifts. To me this is more important than another 100+ fps at the muzzle--which makes less difference than the ballistic coefficient of the bullet. But ever since "affordable" chronographs appeared around 30 years ago, many handloaders have been obsessed about another 100 fps....
