I have recently been informed that RS60 has a lower burn temp than Varget.
Although 'single-based', H4895 and VarGet are very 'hot' powders with 'heat of explosion' values that exceed those of many 'high energy' or double-based types. That's why they often give such high MVs in suitable cartridges.
There is another factor though in comparing RS60 v VarGet and say H4350. The Swiss powder is one of Nitrochemie's 'EI' grades which use the advanced deterrents infusion process that gives a longer lasting effect than plain surface coating which is the norm. Watch the video interview here:
Alliant Reloder 33 « Search Results « Daily Bulletin
What 'EI' technology does is to stretch out the controlled burning period over a longer timespan and flatten the peak of the pressure curve that shows in pressure v time graphs. What's not to like? you ask. Well, elapsed time from ignition also = bullet movement. So, the period of peak pressure / temperature 1) lasts longer than in conventional powders, and 2) affects a greater length of chamber throat / early part of the rifled barrel. It's wear here that determines barrel life and with this powder characteristics, the badly worn part of the barrel is both longer and occurs quicker than with an equivalent pressure from a conventional powder.
(The same effect occurs in use of a heavy bullet with a slower burning powder than from light bullets using a matching faster burning powder grade. Because a heavy bullet has greater inertia, it starts moving and picks up speed more slowly and a powder that initially burns more slowly is used to keep pressures in check. But the slower moving bullet sees the throat / back end of the barrel subjected to peak heat and pressure for a longer period and they therefore erode and/or firecrack quicker. So, today's F/TR 308 Win shooters using 200gn bullets are seeing short barrel life by 308 standards compared to 'Target Rifle' / Palma competitors using 155s, all other factors being equal. This applies even with relatively cool burning single-based grades such as Viht N150 which is popular with 185-200gn bullets in long-range match loads.)
This isn't a criticism or RS60 or the other 'EI' grades. You get the extra performance, but nothing comes free. To put it into context, if conventional powders give a particular weight bullet 2,800 fps in a given cartridge at full pressure loadings, the traditional way of raising that to say 2,900 or 3,000 fps was to use a larger cartridge whose case held a heavier charge and a slower burning powder was usually, but not always, required to suit the new case/charge to bore area ratio. 2,900 is a 3.6% MV increase over 2,800 and 3,000 is 7.1% rounded to one decimal place. The rule of thumb is that all other things (bullet, barrel length and peak pressure) staying the same, an X% case capacity increase generates an X divided by 4 % MV increase. So using conventional methods, 3.6% higher MVs needs ~ 14.4% case cap increase and 7% + MV needs getting on for 28% more case and appropriate charge.
Taking a real life example, RS60 will enhance the 284 Win's performance with a 180gn bullet by by 150-200 fps in a 30 or so inch barrel if loaded to maximum allowed pressure, ie from 2,800-2,850 up to 3,000 or so fps. To achieve that top end figure through adopting a larger 7mm cartridge, we'd need to enhance the case capacity and charge by somewhere in the 25-30% range to a case holding around 82 - 85.8gn water, as the 'straight 284' case holds around 66gn. The primary larger sevens above the 284 are 7mm SAUM at 72.6gn water capacity, WSM with 81gn and 7mm Rem Magnum with 82gn. So, RS60 is potentiually capable of producing something getting on for 7mmWSM / Rem Mag performance at equivalent pressures. (The larger case jobs may still outperform the 284 / RS60 combination though if loaded to their very high 65,000 psi allowed pressures and/or are loaded with a suitable burning rate powder with a higher energy content than the RS grade.) Using the conventional approach, you'd expect a significantly shorter barrel life from the WSM / RM than from the 284 with the same bullet as well as more rapid barrel heating. RS60 may or may not do the job more efficiently than 'going bigger' - I suspect it does - but there is nevertheless no free lunch in ballistics or the laws of thermodynamics, so there still has to be a significant cost to be paid for such significant gains.
