Re: Mixing powder !!!??
SOME things work a little, some have no proof. In the 1k BR game, very few things give "major" improvements, but you might find things that individually give minor improvements but when groups are measured to .001, ever little bit helps.
Start with the best brass, best bullets and barrels. After that consistency in loading technique (seating force, annealling etc) to control neck tension.
IF it makes you feel good and you have the time, go for it but do not expect dramatic positive results. It often goes the other way.
Change one thing at a time, test, repeat and repeat again.
some guys weigh primers. does it work? my Ohaus digital scale weighs to .001 and not sure what they are actually weighing so I never went in for that.
I Juenke bullets except clinch rivers and BIBs. I juenke fired cases. I ream flasholes, sort to .5% of weight (no more which means .5 gr normally), I ream primer pockets, neck turn and trim, seat with arbor press with dial indicator, anneal case necks. I sort all other bullets by base to ogive, weight etc I have repeated tests to prove to me, that those things work for ME in 1k BR with my calibers and guns.
Back to the original issue, mixing powder and duplex loads. 99.9% of most reloaders do not have the experience to even attempt it safely. They have a hard enough time building accurate and consistent handloads with what they currently use. Very damn few cartridges really need a mixed powder load in reality. we have good powders all the way up through 50 cal so just what cartridge really NEEDS a mixed or duplex load? If not careful, it is an accident waiting to happen. Might only be a ruptured case and broken sear but it could be more significant and for no useful purpose in reality.
Reminds me of the times when we used to use a B1 can(OK for you young whipper snappers, that is the small can out of the C-rations of years ago) of gas in the bottom of a hot mortar tube before we dropped a round to get an extra 300m when we needed. Not accurate or safe, but desperate times called for desperate measures.
3 Powders are in between Retumbo and 50 BMG on the burn chart. no need to mix!
167. Retumbo (Hodgdon)
168. H870 (Hodgdon)
169. N170 (Vihtavuori)
170. 24N41 (Vihtavuori)
171. 50 BMG (Hodgdon)