Why are the advantages/disadvantages of a single based powder?
In practical terms - none.
Many people believe that because 'double-base' powders incorporate an amount of nitro-glycerine in addition to the base cellulose, that they run 'hotter' and burn the barrel throat out quicker. Some early DB propellants such as the original 'Cordite' used in pre-WW1 .303 British service ammunition used a very high N-G content and additive technology was either in its infancy or non-existent at that time giving DB types a bad name. The original British Cordite mix was 56% NG, was very erosive, and burned Lee-Metford barrels out in around 1,000 rounds (this is also why the British changed to the deeper / sharper 'Enfield' rifling form). Modern DB powders use relatively small NG contents and incorporate means of keeping flame temperatures down.
Having said that, many DB powders such as the Vihtavuori N500 series and Alliant Re17 are promoted on the basis of high-energy / performance in order to produce higher MVs within allowed pressures. You rarely if ever get anything for nothing, so if you're seeing an extra 100 fps from N540 or Re15 over VarGet or IMR-4064, you'll also see some reduction in barrel life.
On the IMR-4064 v VarGet issue in .308W, I had an FN SPR that produced tiny groups with the IMR powder but never liked VarGet with any bullet weight (most unusual in my experience as this is usually an excellent performer in the cartridge). Unfortunately, my 4064 match load worked up in late winter / early spring disappointed in summer competitions even in the cool British summer. A retest showed that higher temperatures had raised MVs 30-40 fps and took it out of the barrel sweet spot. In the event I moved to heavier bullets and used Viht N550 double-base powder to get the long-range performance I needed from this 24" barrel rifle.
Personally, I would never switch between Re15 and VarGet on the basis of the single versus double-base form issue alone. They're both excellent performers, but VarGet is less temperature affected, while Re15 meters much better in powder measures in my experience. VarGet burns more cleanly than Re15 in many applications - but these pros and cons are marginal.
If GSP7 is worried about Re15's effects on barrel life, working a new VarGet or 4064 single-base load up will probably cause a greater reduction than any increase provided by using a new powder. If worried about barrel life, reduce the load, pressures and MVs to the minimum levels that give acceptable performance - that'll make a much bigger difference!
Laurie,
York, England
