I'm on the same boat but, here's what I gathered so far. For 300 grain SMK... 94 grain of H-1000. Went out this morning fireforming brass using 250 SMK and 94 grain of H-1000. Here's 2-3 shot group at 100 yards.
To achieve the maximum possible accuracy, all variables must be remove or at least minimize.
loads for .338 Lapua Ackely Improved is consisting of 110.5 gr of US869 yielding 2980fps in 20degree celcius temperature, and groups of .557 at 300metres (yrds) this is in an ATR Nesika Custom rifle by LongRanger