I am confident that N550 will take me to my goal. N560 may also do so, if it fits in the case.
N550 is proven to work very well in this set-up, but most UK FTR shooters use N150 as it provides almost as good MVs, is very consistent, and ignites very well in small primer Lapua brass.
I ran the 185 Juggernaut in its early days in large primer Lapua very successfully with N550, and one of our top FTR shooters ran 210gn Berger BTs over N550 very successfully indeed and with barrel life no worse than those using single-based powders from the beginning of the class until he retired from prone rifle shooting about four years ago. This encompassed both large and small primer Lapua brass. I can't remember his MVs, but they were high, though not startlingly so, for 210s (32-inch barrel). Despite being told he would have no end of pressure problems with N550 and heat, he shot the entire program with his UK load over the US F-Class Nationals and World Cup events at Raton in August 2013 in what we were told were high temperatures for the area that year. That included participating in a four-shooter 'Rutland' team in both events as well as the individual matches, and his rifle was used by a second shooter too, so the round count was extremely high.
N560 is a very slow burner indeed - much 'slower' than its N160 base version and IMO, also 'slower' than H4831. It is
much 'slower' than N550 - burn-rate charts IME/IMO put N150/550 as far too 'slow', and N560 too 'quick'. Having used N560 for some 20 or so years in cartridges with
much higher case capacity to bore area ratios than the 308, my experience is that it needs to achieve high pressures before it performs - which you've no chance of producing in 308. I look forward to seeing your results, but would be very surprised if you get satisfactory MVs and consistency.
As an add-on, we (and the Australians and Canadians) have a prone 308 Win discipline that has no US equivalent - Match Rifle. This is in rifle specs and shooting regulations like a half-way house between 'Target Rifle' (Fullbore / Palma to you) and FTR, long predating the latter. Any sights are allowed but various changes include a 5.5lb maximum barrel weight. MR runs very long barrels chambered with
vast amounts of freebore and heavy bullets. As the three stages are 1,000/1,100/1,200 yards in an MR match, (up to 1,500 yards on one Australian range), MV + elevation consistency are their gods. (They use standard NRA / ICFRA TR targets, not the half-diameter F-Class targets.) They're a secretive bunch re their loads but are notorious for innovation and trying every powder / bullet combination that might work, often pushing pressures to the limits. I've never heard a hint that any use N560, but 550 was common at one time. Rumour has it that Alliant Re17 / Nitrochemie Reload Swiss RS60 is their favoured fuel these days and I've been quoted some 'interesting' loads and impressive MVs. This is a known temperature-affected powder as previously noted, but we can usually 'get away with it' in the British Isles. Whether the Aussies, (who see AZ type temperatures), do so is a moot point, unlikely I would think!
