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I know it has probably been asked and answered, but for some reason I have spent a couple houses with the google and it has failed me (or I failed it by typing in the wrong thing).

I saw some posts by HTR where he made up some loads for a 130 subsonic bullet using either Trail Boss or Unique. I have Unique so that is what I want to use but in all the posts and threads I have seen on it I only saw the grain amounts for Trail Boss mentioned and then it just stated that Unique was tried and worked well too.

How many grains of Unique should I use for a subsonic load?

Noveske 6.8 SPC 1:12 twist barrel - 14.5 inches
130 grain Sierra Hot-Cor projectiles
SSA Brass (old SSA)
CCI Small Rifle Primers
 

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In my opinion, the answer is none. My reasoning is that the 6.8 case is too large for reliable ignition of a miniscule charge of Unique. When loading subsonic, you are already flirting with the possibility of a stuck bullet (bullet in Bore) event.

Trailboss will nearly fill the 6.8 case, and will yield much better ignition and smaller spreads.

Most articles suggest starting with a full case of TB, shooting over a chronograph. Decrease the charge slowly until the desired velocity is reached. This load is likely to be usable only on your rifle with your selection of components.
 

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I had a 7x6.8 bolt gun . (It's a long story with a happy ending)
I shoot cast bullets almost exclusively in everything. In the straight neck up I used a 150 gr cast and reduced the UNIQUE charge down to 3.5 gr before I got subsonic. To keep perspective that's about the same charge as a start load for a 125 gr 9mm and a 158 gr 38 special takes 5.5 as does a 230 gr in 45 ACP. I wouldn't do it with jacketed and Unique at all.
 

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... Trailboss will nearly fill the 6.8 case, and will yield much better ignition and smaller spreads.

Most articles suggest starting with a full case of TB, shooting over a chronograph. Decrease the charge slowly until the desired velocity is reached. This load is likely to be usable only on your rifle with your selection of components.
I briefly tried TB under some 130's and found that a charge in the upper 8's was still a little supersonic out of a 16" barrel -- so with your shorter barrel, about 8.5 grains of Trail Boss would be a good starting point.

Be advised though that with your 1:12 barrel, the 130's may tumble
 
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