There's a bit of chemists' semantics in all this. Nitrochemie says on its website that all of its powders are 'single-based', yet some grades, as with the Viht N500s, contain nitroglycerin. (That includes the three Alliant grades manufactured by Nitrochemie.) I had a discussion with the UK distributor about this, and the answer was on these lines:
If you start with just nitrocellulose as the primary ingredient, it remains 'single-based' as far as industry chemists are concerned, no matter what you do at late stages to the part-finished nitrocellulose product during the production processes. As the name suggests, there is a single primary ingredient.
If nitroglycerin is mixed with nitrocellulose in the early 'dough' phases, it's a double-based product as there are now two primary ingredients. (Or triple-based with many artillery propellants etc with another explosive mixed in.)
Now, around 30 or more years ago, Nitrochemie developed a patented process to take the base nitrocellulose and infuse a carefully controlled amount of nitroglycerin into it from the outside. It later sold this technology to Vihtavuori which uses it in manufacturing its N500 series grades. AFAIK, no other manufacturer uses this method. Such products are still classed as single-based in the industry, but ascribed a new classification - 'High Energy'. Which of course is exactly what it used to say on Viht's N500 product labels in stonking great big letters. (Not anymore in the current rebrand interestingly, though.)
So Nitrochemie and Viht are technically correct to describe such products as 'single-based', but the handloader is more concerned about the existence or otherwise of nitroglycerin being conditioned to be wary of its effects on barrel life. (Actually, I believe we've now possibly worried over-much about this, and true single-based powders burn barrels out just as quickly when you use small-primer brass and run at very high pressures. Some single-based products are also very 'hot' indeed when you look at their combined heat of explosion values, H4895 and VarGet included which exceed those of many 'double-based / high-energy powders.)
The other thing to note is that nobody has introduced a new single-based handloading propellant that I can think of for many years now, with the possible exception of ultra slow-burning 50BMG types. All recent Viht introductions are N500s (N555, 565, 568); likewise all Alliants and IMRs (the ill-fated 'Endurons'). I'm probably wrong here, but the last single-based mainstream powder introduction I can think of was Hodgdon/ADI's IMR-8208 XBR back in 2010. Explosia's tubular Lovex S0-65 (Shooters World 'Long Rifle') was a few years prior to that in Europe, and that's about it. There must be a reason for this wholesale switch to using nitroglycerin - whether for environmental regulations or the customers demanding ever-higher performance, I don't know.
www.vihtavuori.com
