RS40 is a fast burning 'high-energy' (infused nitroglycerin) canister version of the Swiss 5.56mm GP90 service rifle rifle round's propellant. It is a 'hot' number and on the fast burning side for 308, but sometimes does well in this cartridge with lighter bullets - up to 155gn. Above 155, it can be used but loads have to be heavily limited to avoid pressure spikes and even with 155s it has acquired a reputation for proving inconsistent in match use. I've seen more F/TR shooters run into problems and retire with RS40 than though any other single reason going back to when it had a burst of popularity in the discipline.
The two RS grades that are ideally suited to the 308 and a wide range of bullet weights therein, are RS50 and RS52. RS50 is the plain-Jane single-based version, and its characteristics and performance are very close to those of Viht N140. They are so close in fact that when the powder first appeared here as an entrepreneurial venture and before the Swiss manufacturer Nitrochemie set up the Reload Swiss operation in the UK, it was called 'TR140' and with no loading data the instructions were to use those for N140 ........ which worked just fine as it turned out. (I did a side by side test with N140 in both 223 Rem and 308 Win at that time and MVs were so close that they could have been from different production lots of a single product.) Fans of RS50 actually consider it better than N140 as it is a bit more flexible and will often allow higher charges / MVs before running into pressure issues, but I can't confirm that one way or the other.
RS52 is a short-cut 'high-energy' (infused nitroglycerin) type that also benefits from Nitrochemie's unique EI infused deterrents technology to control the initial burn better and spread it out over a longer period. Nitrochemie describes it as the ideal 308 Win powder, and there is more truth than hype in that. It really is a flexible, well mannered propellant in this application and handles nearly all bullet weights up to those above 200gn giving high MVs (if needed and so loaded for).
Bering a 'double-based' type in most people's eyes (nitroglycerin used in the formulation) many become scared of it because of reduced barrel life, but this shouldn't be a great issue if loads are kept to moderate levels.
RS60 and Alliant Reloder 17 are one and the same thing, the powder bulk shipped to the USA for bottling under the Alliant banner. It is too slow burning for 308 with the possible exception of heavy bullets of 200gn and up. RS60 like RS40 is a 'hot' number and can give spectacular performance in some cartridges, especially 6-7mm designs, as much as an extra 150-200 fps for 105gn bullets in long-barrel 6XC match rifles for example. However, if loaded up this heavily in this sort of cartridge, it also causes spectacular barrel wear, so has acquired a reputation as a 'barrel-burner' and saw a lot of people drop it rather quickly.
It is heavily touted in its Re17 version by Alliant ATK for the short magnums and really is a great performer in 270-300WSM and SAUM and is rightly popular among medium to heavy game and long-range game shooters in the USA. It's not a great choice though for 308.
what bullet was you using ?
