Sub loads for a 8.5" barrel?

[Skulls]

Need some help getting started with my subsonic loads.

My setup is a:
TP555 8.5” with 1x8” twist barrel
adjustable gas block in pistol position

Powders I have available:
Accurate 1680 & 5744
Hodgdon H110 & Lil Gun
IMR Trail Boss

Bullets I have available:
Hornady 180gr SST & 180gr BTSP Interlock
Speer 180gr Spitzer

I know I should be using something heavier, but have not been able to find anything locally and I have a few hundred of the above on hand, which I was using to load 308 subs.

Brass:
1000 pieces mixed that I purchased from Hoser

Fed Small Rifle Primers

I also have a question about using the chamber gauge I purchased with my barrel. Out of a hand full of brass that I have tried some will drop all the way in flush with the gauge and others will stick out a little bit. Looks to be around the width needed for the extractor to grab on to the case.

When seated should the bullets tip stick out of the end of the gauge or should it be flush?

Thanks for the help