Add the additional buffer if needed. Pressure signs are just like rifle pressure signs, rim will bulge or get thicker, lettering will get flat, and primers will be easily pushed out of the case with a straight large paper clip. If you start shooting cases with loose primer pockets, a primer will come out after firing and end up in the action or trigger group.
I always examine the wads on fired rounds when working up loads. If the load burns up the wad or tears up the wad in a very strange way, it indicates that the load may not perform the same from shot to shot. At a certain point, the pressure will burn through or blow out the gas seal on the wad's base, which gives erratic ignition.
You may play with lubing up your wads with motor mica to ease the pressure some.
I learned from an Olympic shooter that plastic in the bore dramatically distorts patterns. So, examine your bore keep the plastic out of the bore, and choke. I can not stress the clean bore issue enough, it was a humbling thing to learn in my testing. Also, some wads will deposit more plastic in the bore than other brands or types due to the different materials they are made of.
Again, Bubba Round Tree on You Tube, Face book is a world of knowledge in loading large shot and buckshot.
TSS is so expensive, I can not afford it, but I do mold my buckshot with a mix of 50/50 linotype and wheel weights which is MUCH harder than anything you can buy. The Hard buckshot sold by Ballistic Products is darn good buckshot. The T shot sold by Ballistic Products will kill coyotes a long ways out there with Bubba Round Tree's loads.