I have the 9mm taccom ULW 5" barrel with 16" shroud.  It is plenty accurate out to 25yds, but at 100 yards its like 3 foot groups with Freedom Munitions 115 gr and WWB 115 grain.
AAAANNNNDDDD some of my local buddies have figured this out and have started making stages with 75-100 yard shots.  Last time I fired 3 shots supported and well aimed at each of 6 targets and got 3 FTN's.

SO now that I have the dillon out, how do I make ammo that will shoot in this barrel?  Should I be trying heavy bullets so they stay subsonic or what is the trick to 100 yard accuracy for PCC.

Either sub or supers will work fine. I'd probably pick 115s if I was really going to be making shots out that far. For the best accuracy, treat it like a precision rifle. Figure out your distance to the lands (or when the round just barely passes the plunk test), take it a few thou off the lands, then play with charge weights until you get acceptable accuracy.

Try 115 and 124/125 JHPs, Montana, Hornady XTP or HAP.  Use fast powder like Titegroup since you got only 5" for it to burn.

Its the 115s for sure. They go all over the f place past 25 in either my scorpion or mpx. 124s and 147s are stupidly consistant. If reloading those 124gr rmrbullets fmjhps are VERY good accuracy wise im using them with CFE pistol powder and cci prime

Winchester white box and umc were the worst 115s i tried. The speer lawmans were best but once you go up to 124 ir higher its way better

Op here

Tried aguilla 147gr fmj flat point and got about a 6in group at 100 yds. 3 in group at 50 yds. It's definitely hotter than the freedom munitions. This is good enough for me so I don't plan on trying to load better on the Dillon 550. I'm going to start putting 2 of them in the bottom of every magazine as a warning for low ammo.