Have .223 and 5.56 marked cases with primers that weigh between 91 grains up to 104 grains. IMI SS109 marked brass weighs 98.6 grains, this brass was from a production run done around 2000. .Point is, have some 223 and 5.56mm brass that is as heavy , and 223 and 5.56 brass which is light. I'll take a sit in front of the TV, with an electronic scale and separate mixed brass into three piles, 91 to 95, 95 to 100 and 100 to 104. Obviously a 101 grain case is around 10% thicker than a 91 grain case, and hot load in a 91 gr case maybe over pressure in a 104 gr case. . If you are going to hot load all cases with the same load trying to reach full 5.56 fps, build the load in the heavier cases, as it should then be as safe to safer in the lighter higher volume cases, thou velocity will fall a bit. Looking at online actual factory 5.56 ammo velocity tests, some 5.56 is in the 233 velocity range, the rest are normally about 100/150 fps hotter than a max. loaded .223. In the real world, 5.56 is usually not as hot loaded as people believe.. I load the same accurate hot 223 load, in all the case weights. The heavier cases deliver about 50 fps (with not to scary pressure signs) more than the lightest cases with the same charge, and are stored as the SHTF loads, because they are very close to a true full mil spec 5.56. So in essence you can move from a hot 223 load to a very near full mil spec load, by using the same load in different weight cases. Reloaders who concern themselves with placing 5.56 pressure loads into a .233 need to be aware of the effect of case weight on pressure/velocity, case sorting and a chronograph would insure the goal is achieved.
5.56 has a higher pressure based on the early tracer bullet, which is longer than SS109/M885, and is why the lead/pressure was increased in 5.56. So if you are not firing 5.56 tracers and otherwise keeping off the lead .....??
