Bryn .... be very careful with the data in the UKV thread. It is for Small Rifle primed brass. SR ignition is much less vigorous than with Large Rifle and will change maximum loads by 1 to 1.5gn. Using SR brass data in LR brass loads can see OTT pressures very quickly. Secondly, SR Lapua brass (and I suspect Peterson too having compared the two makes in the not too different 260 Rem is a heavier case with less internal capacity than the Hornady which again changes the internal ballistics, quite significantly here.) Thirdly, the SR brass is VERY strong compared to Hornady - people are routinely running pressures in their SR 6.5 Creedmoor handloads that will kill Hornady in a couple of firings, may even see blown primers from the 'off'. (SAAMI lists the cartridge as 62,000 psi MAP and Lapua / Peterson SR brass allow that - and more - with comfort. Hornady loads its factory ammunition to 56,000-58,000 psi and frankly that is all Hornady cases will accept and still give a reasonable life.)
So, a maximum safe load (of any bullet / powder combination in SR Lapua / Peterson brass is potentially - I'll go further and say probably - too high for Hornady, and in fact likley to be unsafe.)
SR ignition (including the smaller diameter 'flash-Hole 1.5mm v the standard 2mm) also gives cartridges very different burn and pressure-rise characteristics from LR versions. So, there are in effect two cartridges here (and in 308 between standard LR brass and SR 'Palma' versions) sharing the same name. Most published loads data from bullet and powder manufacturers is for Hornady brass, but Viht's data are based on SR Lapua.
RS62 is very well suited to the cartridge in either form and is probably the best alternative to the now unavailable H4350, although IMR 'green' and Reach-compliant 4451 grade is very close in this and other cartridges to H4350 and has full data on Hodgdon's online reloading center facility.
When I had a play with the cartridge two years ago in a loaner Savage 12 LRP, I worked up to 45.0gn RS62 with the 123gn Scenar and 43.5gn RS62 with the 142gn Sierra MK. 43.5 RS62 gave the 142 2,842 fps in the 26-inch barrel LRP without any apparent pressure problems. This was in Hornady brass and with the mild CCI-BR2 primer.
In heavier but still LR Norma brass (superb quality and strong, much better than Hornady) I loaded the 140gn Nosler Custom Competition which the Savage liked more than the AMax, Scenars, or SMKs. Using H4350, IMR-4451, and RS62 loads were worked up to 42.4gn H4350; 43.3 IMR-4451 (it needs another 0.5-1gn over H4350 to achieve same MVs in the Creedmoor); 43.5gn RS62. Charges above 42.2gn RS62 in the Savage produced larger groups and I settled on a relatively mild/slow 42.2gn for 2,712 fps out of the Savage but which shot quarter - third inch at 100 and gave me a sub 6-inch 1,000 yard group in a BR competition. Nodes for your rifle / barrel won't be the same, you have to find them. These loads were in Norma brass with the BR2.
In summary, my testing suggested usable loads for IMR-4451, H4350, and RS62 are all close to each other. RS62 and IMR-4451 needed slightly heavier charges than H4350 to produce any given velocity in that rifle. This allows the widely available H4350 data to be adopted to provide starting loads only for RS62, and data must never be simply substituted or listed maximum charges for one to be regarded as safe with the others.
Muir. Lovex SO70/SW-4350 is an excellent powder in the 4350 general burning rate category. If you dig out your old reloading manuals of 12 or more years ago, this was what was then distributed in the US as AA-4350. (This was before Western Powders bought Accurate and switched suppliers from Explosia a.s. to General Dynamics Energetics, Valleyfield (the IMR manufacturer). I suspect today's Accurate-4350 available in the US (but not here) is IMR-4350 under a different label. (Of the other Explosia powders being imported to you by Shooters World, SO62 - forget its SW designation - is the old AA-4064 of the pre Western Powders period and is exactly what IMR-4064 does. An excellent 308 Win powder for instance in mid-pressure general match and hunting loads.)
IME you'll be disappointed if you expect H4350 performance though. SO70 is a competent performer but not outstanding whilst H4350 is (alongside Europe's RS62) the class leader in terms of the velocity / pressure relationship and flexibility.
